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Offshore geohazards Summary Report Research institution-based strategic project 2002 - 2005

NGI-Report 20021023-28 December 2005

Salt diapirs, Gulf of Mexico (Courtesy of USGS)

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SUMMARY This report summarises the Research institution-based strategic project (SIP) - Offshore Geohazards. The project was performed during the period 2002-2005, by the Norwegian Geotechnical Institute (NGI) and funded by The Research Council of Norway. The project was carried out in close co-operation with the International Centre for Geohazards (ICG) at NGI. The main objective of the SIP “Offshore Geohazards” has been to improve, develop and verify methodologies and techniques to reduce the risk associated with offshore geohazards. Geohazards are defined as local and/or regional site and soil conditions having a potential of developing into a failure or accidental event causing loss of life or damage to health, environment or assets.

During the 1990s petroleum exploration and field development activities expanded to continental deepwater slopes and into water depths larger than 1000 m. Offshore exploration and field development were also initiated in tectonically active areas like the Caspian Sea. These were new areas with potential geohazards, and little experience was available regarding geotechnical soil conditions, geological processes and human activity that could affect oil and gas field development. Seabed deformations and instability, mass movements, gas and water flow generated by natural processes or human activity, may cause damage to and loss of platform wells and risers, foundations and anchors, subsea structures, pipelines and control cables. Submarine slides or mass movements have been the central scientific topic in the SIP. Slide scars and debris deposits from enormous submarine slides have been observed along the continental slopes around the world at slope angles less than three degrees. Several slides are of Holocene age (<10,000 yrs BP). With

Offshore geohazards that may have to be considered during development oil and gas fields

Geohazards are defined as local and/or regional site and soil conditions having a potential of developing into a failure or accidental event causing loss of life or damage to health, environment or assets.

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increasing seismic mapping of the slopes an increasing number of older slides (paleoslides) buried by more recent sediments have been found. Large scale slide events have generated tsunami waves impacting coastal areas. Rapid deposition of sediments and tectonic compression generate high excess pore pressures, causing reduced soil strength and thus increased likelihood of seabed instability, both at large scale and locally. Excess pore pressure also contributes to active faulting and formation of salt and mud diapirism, mud volcanoes and fluid escape features like pockmarks. Human activities like drilling and production and installation of structures may also alter the conditions locally, and trigger mass movements. The SIP has contributed greatly to the understanding and assessment of offshore geohazards. The benefits include improvements in: • the understanding of seabed instability mechanisms • the modelling of mass flow and fluid and gas transport • the tools and methods for the assessment of material properties and design

parameters • the quantification of uncertainties and frequency of geohazard events • the assessment of the consequences of offshore geohazards This new knowledge will enable a more rational assessment of geohazard risk and give valuable assistance for: • identification of geohazards • production of geohazard maps and optimisation of field lay-out to minimise

hazard and risk • evaluation of measures to reduce risk of damage to wells, field installations and

environment By combining research with consulting work, NGI is able to apply results to practical situations. NGI has used the results of the SIP research to develop best practice guidelines. The SIP has thus strengthened NGIs position as a leading actor in research and consulting work related to offshore geohazards. NGI wishes to thank its clients in the oil and gas industry for giving NGI the opportunity to participate in challenging and rewarding offshore geohazard studies. The results of the SIP could not have been accomplished without these studies. NGI extends its gratitude to all individuals, companies, institutions and universities that contributed to the successful completion of this SIP!

This report is also available on the NGI WEB site www.ngi.no

Reduced risk

The SIP has strengthened NGIs position as a leading actor in research and consulting work related to offshore geohazards

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CONTENTS 1 OBJECTIVES 5 2 ORGANISATION 6

2.1 Budget and schedule 6 2.2 Co-operation and education 6

3 SCIENTIFIC TOPICS 7

3.1 System definition - Mapping, monitoring and soil investigation techniques 9 3.2 Geohazard identification - Triggering mechanisms and failure scenarios 9 3.3 Geohazard risk estimation - Consequence analysis 10

4 SUMMARY OF RESULTS 11

4.1 Mapping, monitoring and soil investigation techniques11 4.2 Triggering mechanisms and failure scenarios 16 4.3 Consequence analysis 18 4.4 Best practice 21

5 BENEFITS 21 6 REFERENCES 22

6.1 Published papers 22 6.2 Published lectures and presentations 25 6.3 NGI-reports 29 6.4 Press and media coverage 31

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1 OBJECTIVES The objective for a research institution-based strategic project (SIP) funded by The Research Council of Norway, is to create high-calibre research groups in their spheres of responsibility or to build up new communities in areas of strategic significance through basic research, applied research, competence building or restructuring (www.forskningsradet.no). The main objective of the SIP “Offshore Geohazards” proposed by NGI in 2001 and funded by The Research Council of Norway during the period 2002-2005 has been to improve, develop and verify methodologies and techniques required for assessment of offshore geohazards. During the project period this objective has been met by developing improved: Mapping, monitoring and soil investigation methods and techniques for • detection and monitoring of

potentially unstable areas, slide triggering sources and special geological features with potential for damaging wells and field installations

• quantification of soil properties, pore pressure conditions, gas content as well as presence and stability of gas hydrates

• mapping of large areas with potential geohazards

Understanding of the physical processes and material behaviour related to sub-marine slides or mass movements, for example • triggering sources and

retrogressive sliding mechanisms • mechanical behaviour of

submarine sediments and effects of gas and gas hydrates

Analysis methods and numerical models for • slope stability analysis • simulation and animation of

submarine mass movements • evaluation of consequences, for

instance run-out distance and impact forces on structure

The main objective of this SIP has been to improve, develop and verify methodologies and techniques to reduce the risk associated with offshore geohazards.

Seabed bathymetry from the Storage slide scar at Storneset (Courtesy of Hydro)

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2 ORGANISATION 2.1 Budget and schedule The SIP has been conducted during the period 2002 to 2005 with a total funding of 14 million NOK from The Research Council of Norway and 2.8 million NOK from NGI.

2.2 Co-operation and education An Advisory Group has been active in the project period to promote interaction among the different contributing partners and other interested parties. An important function for this group has been to enable possible adjustment of the research aims during the project. The Advisory Group has advised NGI on the aims and directions of the work, given feedback on the obtained results obtained and provided information and opinions on the needs of the industry. The groups’ members have included: • Are Birger Carlson, The Research

Council of Norway • Anders Elverhøi, University of

Oslo • Steinar Nordal, Norwegian

University of Science and Technology (NTNU)

• Stein Bondevik, University of Tromsø

• Tor Inge Tjelta, Statoil • Tom Guttormsen, Hydro The SIP has been carried out in close co-operation with the Centre of Excellence; ICG. NGI is the host organisation for ICG, and the SIP has

been a step-stone and an important contribution to ICG. The research activities conducted in the project have involved co-operation with many companies, institutions and universities: • AP van den Berg, Netherlands • BP, UK • Brit Survey (Fugro), UK • Geological Survey of Norway

(NGU), Norway • Hydro, Norway • IFREMER, France • Imperial College, UK • Institute for Geotechnical

Engineering, ETH Zurich, Switzerland

• Lankelma, UK • NaDesCoR (Natural Disasters

Consulting and Research), Switzerland

• NORSAR, Norway • Norwegian University of Science

and Technology (NTNU), Norway

• PLAXIS BV, Netherlands • SINTEF, Norway • Statoil, Norway • Total, France • University of Bologna, Italy • University College Dublin, Ireland • University of Massachusetts, USA • University of Oslo, Norway • University of Tromsø, Norway • University of Washington, USA Two PhD students, both employees of NGI, have been connected to the project. In addition, several post doctoral candidates and visiting researchers have been involved in the SIP research work.

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3 SCIENTIFIC TOPICS Slide scars and debris deposits from enormous submarine slides have been observed along the continental slopes around the world. The explanation for the slide activity in the deep waters and the risk assessment related to instability of the remaining slide scarps are important aspects of geohazards evaluations. Large submarine slides may generate tsunami waves that can devastate the coastline areas. The understanding the large scale geological processes is therefore important for the evaluation of these effects on development of oil and gas fields. The geohazard risk assessment in the SIP uses a risk analysis framework according to international standards and terminology. Risk management is an integrated process, with several levels, back-steps and iterative loops. Most risk assessment frameworks contain: hazard identification, hazard analysis, consequence or elements at risk identification, vulnerability analysis, risk quantification or estimation, risk evaluation and risk management. There are two approaches to risk assessment, a qualitative and a quantitative. In qualitative risk assessment, the components of risk are expressed verbally and the final result is ranked or given as verbal risk levels. Quantitative risk assessment involves quantification of hazard and risk components and computation of risk from these

components. The quantitative risk assessment frameworks proposed in the literature have the common objective of answering the following questions: • What are the probable

dangers/problems? [hazard identification]

• What is the magnitude of dangers/problems? [hazard analysis]

• What are the consequences and/or elements at risk? [consequence/elements at risk identification]

• What might be the degree of damage in elements at risk? [vulnerability analysis]

• What is the probability of damage? [risk quantification/estimation]

• What is the significance of estimated risk? [risk evaluation]

• What should be done? [risk management]

The process to determine offshore geohazard risk may be illustrated by the flow diagram based on the NORSOK standard Z-013 for risk management shown in the figure below. The sections of the process where the geological and geotechnical aspects are major are marked with pink colour: System definition, Geohazards identification, Geohazards risk estimation and Geohazards risk evaluation. The SIP has focused on the three first sections.

The NORSOK framework for risk analysis has been used

Geohazards are defined as local and/or regional site and soil conditions having a potential of developing into a failure or accidental event causing loss of life or damage to health, environment or assets.

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The SIP has been organised in three main parts: 1. System definition - Mapping, monitoring and soil investigation techniques 2. Geohazard identification - Triggering mechanisms and failure scenarios 3. Geohazard risk estimation - Consequence analysis, slide run-out, impact forces

and tsunamis The scientific content and results from each project part are summarised in the following sections.

Offshore geohazard risk assessment process, based on NORSOK Z-013

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3.1 System definition - Mapping, monitoring and soil investigation techniques

Field description is part of the system definition. Elements like geological history, evaluation of case studies, site investigation and field instrumentation are included. In this quantitative geohazard evaluation stage, the engineer is always faced with limited data about the area of interest. Representative geometry and input parameters for engineering calculations within the study area have to be selected. Methods to map and describe areas with large

amounts of available geological data are needed. To be able to determine input parameters for different analyses, field investigations and measurements, including laboratory experiments, are used extensively. Research connected to improving field and laboratory methods and interpretation techniques is essential and have been included in this SIP.

3.2 Geohazard identification - Triggering mechanisms and failure scenarios Evaluation of trigger mechanisms and failure scenarios are part of the geohazard identification phase. Offshore geohazard identification requires the integration of geological and geotechnical knowledge and methods. Geological processes explain the preserve of geohazards and their potential danger. Continuous sedimentation processes take place on continental slopes altering soil properties like the soil strength. Rapid sedimentation may in some cases cause high excess pore pressures. The ability to describe soil material behaviour and strength during loading or deformation, for example during a submarine sliding process, is

vital to be able to evaluate possible trigger mechanisms and failure scenarios. Slope stability is traditionally investigated by using some form of limiting equilibrium method. However, many soil materials, such as sensitive soft clay, may display strain-softening, or a decrease in shear strength with further deformation after peak strength has been reached. Strain-softening has a negative effect on stability and causes progressive failure development. Understanding of pore pressure and gas effects and mechanisms is also essential for geohazard identification.

Model of progressive failure in a long natural slope with strain-softening soft sensitive clay

Research connected to improving field and laboratory methods and interpretation techniques is essential and have been included in this SIP.

The ability to describe soil material behaviour during a submarine sliding process, is vital to be able to evaluate trigger mechanisms and failure scenarios.

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3.3 Geohazard risk estimation - Consequence analysis Consequence analysis is part of the geohazard risk estimation. In traditional geotechnical engineering, the mathematical slope stability model is valid until the soil reaches failure. The result of the analysis is the capacity of the soil. In connection with geohazard risk estimation it is important to be able to continue the failure analysis in order to calculate the velocity of which a slide moves, the soil volume and the area involved, as well as the run-out distance. Numerical simulation of submarine mass flow is thus essential when evaluating slide consequences.

Reliable methods for predicting the dynamic evolution of mass movements or slides are needed. At the start of the movement, the soil has low mobility; but during a sliding process the soil may become more mobile and liquid-like, forming a debris flow or turbidity current. Modelling submarine slides in clayey soils through all these phases of sliding is a challenging task. Submarine slides may generate tsunamis with devastating effects in coastal areas. Reliable methods for modelling of tsunami generation are needed to predict sea level rise and run-up heights.

4

Tsunami impact from the Storegga slide (colours show wave height)

It is important to be able to calculate the velocity of which a slide moves, the soil volume and the area involved, as well as the run-out distance.

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4 SUMMARY OF RESULTS 4.1 Mapping, monitoring and soil investigation techniques

Geophysical mapping methods Drilling into sand bodies containing water under high pressure may cause major problems. The “shallow water flows” that may arise from such punctures will discharge subsurface fluids into the ocean and may damage equipment and delay drilling programs considerably. Methods for localising these over-pressured areas prior to drilling is therefore of great value to the petroleum industry. The benefits of using a seismic shear wave technique for offshore geohazard mapping have been demonstrated. The technique may be used in connection with detection of over-pressured zones, gas hydrates and “weak” layers. The differences in reflection from compressional and shear waves in over-pressured sand bodies were characterised by seismic modelling. The results show that over-pressured sand bodies in many cases will most probably produce large shear wave reflections, but only small compressional wave reflections. “Weak” layers are important in slope stability studies. However, these are often thinner than the typical seismic resolution of a few metres. Tools for processing seismic data were streamlined for geohazard studies in order to improve the identification of these layers. To improve interpretation of site investigation data, geotechnical and geological data as well as the traditional wireline logging data, have been combined in the seismic sections (see figure next page).

Evidence of gas hydrates are traditionally detected by seismic imaging. However, seismic imaging alone cannot estimate the hydrate concentration. Studies performed in the SIP show that it is possible to detect gas hydrates by means of seabed logging.

Read more about: • Seabed shear wave seismics • Shear wave seismic source.

Prototype testing offshore • Using electromagnetic (EM)

waves for mapping gas hydrates • Seismic tools for geohazard

studies

Papers and reports produced in the project are listed in the reference list of this report

Results from the SIP were presented at a number of international conferences, workshops and in the press (see references)

Comparison of reflection from compressional (left) and shear (right) waves identifying an over-pressured sand body

Tools and methods for indentification of weak layers have been improved.

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Resistivity CPT Probable debris flow deposits

BSR

Field monitoring and instrumentation techniques A ”Best Practice" manual for the design of subsea and offshore instrumentation systems has been produced based on 30 years of NGI experience. The manual contains a summary of relevant measuring techniques as well as recommendations for the selection of sensor technology and system solutions. Technologies and techniques for further development and implementation in subsea geohazard monitoring systems at locations without existing infrastructure have been evaluated during the project. The multilevel piezometer string developed during the project provides measurement of pore pressure in soil sediments at several discrete depths within a single boring. The sensor is constructed as a modular unit, allowing variation in the number and location of the sensing points along the string. The

sensor provides important material parameters for geotechnical analysis, as well as significant cost savings as fewer subsea borings will be required to obtain the necessary pore pressure information. Improved methods and equipment to provide knowledge and control of situations with release of gas close to subsea structures or production platforms are needed by the oil and gas industry. Concepts for equipment monitoring the concentration of dissolved gas leaking from the seabed as well as from the subsoil have been studied and evaluated in the SIP. In some cases free gas bubbles can be observed in the field. The amount of released gas (bubbles) among others provides important information. Outlines for a subsea bubble counting instrument to detect release of gas have been developed.

Improved technology for pore pressure measurement reduces costs

Seismics shown together with data from geotechnical site investigation

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Hydrostatic pressure

Piezometer

Piezometer

Layer with

excess pressure

Logger Pore pressure reading

Multilevel piezometer Read more about: • Subsea instrumentation 'Best

Practice' • Multilevel piezometer • Monitoring gas charged seabed

and hydrates • Real time monitoring –

contactless serial interface • Miniature subsea logger

Soil investigation techniques The SIP has contributed to the development of a new seabed sampler (DWS). The DWS can take up to 25 m long high quality soil samples in water as deep as 2000 m. A prototype of the DWS has been built and tested both onshore and offshore. High quality of the samples has been confirmed by field and laboratory testing.

The input to an improved quantitative framework to characterise soft offshore shallow sediments associated with deep water developments by use of situ testing methods have been provided. Read more about: • Geotechnical optimalisation and

design criteria of seabed sampler • Characterisation of soft soils in

deep water by in situ tests

A new seabed sampler taking 25 m long samples has been tested

Detail from subsea instrument

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Laboratory methods Soil samples are disturbed by transportation from the field, handling in the laboratory and during preparation for testing. Because of this, the material parameters measured in the laboratory may not be representative of the actual properties in situ. A procedure for adjusting the soil parameters has therefore been proposed in the SIP. A good determination of the preconsolidation stress obtained from disturbed soil samples was found decisive for the reliability of the proposed correction method. Area for offshore geohazard evaluation – Caspian Sea

10 100 1000σa' [kPa]

35

30

25

20

15

10

5

0

ε a [k

Pa]

Onsøy, 14.2 mUndisturbed, BlockDisturbed, 54 mm

Interpreted pre-consolidation stressindicated by an arrow

0.0

1.0

2.0

3.0

4.0

5.0

Mt [

MPa

]

0 100 200 300 400

σ'a [kPa]

Onsøy, 14.2 mUndisturbed, BlockDisturbed, 54 mm

p'0

Interpreted pre-consolidation stressindicated by an arrow

Left: Stress strain relationship from CRSC testing on disturbed and undisturbed material Right: Tangent modulus values versus axial stress

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The remoulded shear strength is an important parameter for offshore slope stability analyses. Several methods are used to measure and determine the remoulded shear strength. Consequently, the shear strength values used for design can vary significantly. A database containing remoulded shear strength data has been established in the SIP. The measurement of suction in soil samples as a mean to explain anomalies in measured shear strength values and to evaluate sample disturbance have been investigated. Different laboratory techniques were compared and tested. The results show that such data give an indication of sample quality, but the uncertainties are substantial, and results are recommended to be used only in conjunction with other soil parameters.

Correlations of geotechnical index test data

Read more about: • Correction methods for

oedometer testing • Measurement of remoulded

undrained shear strength • Suction in clay samples Databases Databases for geotechnical offshore borings, geotechnical laboratory data, field data, slide and offshore geohazards incidents have been established during the SIP. The purpose of the databases is among others to facilitate the study of large areas and to gather information from for example studies in the same geographical area and similar case studies. The in situ conditions with combined high pore fluid salinity and excess pore pressures make the Caspian Sea sites unique. An index parameter database from the Caspian Sea has been compiled. The database may be used to study correlations between index test data and material properties obtained from more sophisticated test techniques. Read more about: • Correlations between index and

soil design parameters • Offshore geotechnical borings • Geotechnical data • Information system for

geotechnical laboratory data • Improved field monitoring • Slides and offshore geohazards

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4.2 Triggering mechanisms and failure scenarios

Migration of gas Shallow gas may influence the stability of sediments and cause difficulties in drilling operations especially 500 to 700 metres below seabed. The ability to predict the presence and the effects of shallow gas in the vicinity of offshore structures has been improved in the SIP. Basic mechanisms for gas flow and migration in shallow sediments have been identified. Possible methods to simulate gas migration and flow have been investigated. Read more about: • Gas migration mechanisms

Pore pressure build-up during sedimentation Reliable prediction of the pore pressure distribution in the sediments is essential for the evaluation of slide hazard. Pore pressure build-up depends on the sedimentation

process. Both one- and two-dimensional (1D/2D) subsea sedimentation processes have been studied. Read more about: • Pore pressure during

sedimentation

Simulation of water displacing gas

Numerical model of gas flux through sediment

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Progressive failure mechanisms in soft clay Failure mechanisms in deep water with clayey sediments have been studied in the SIP. A progressive failure mechanism in a natural slope with soft, sensitive clays following strain-softening behaviour were successfully modelled and found to cause large-scale failures. Shear bands with strain concentration develop during this kind of failure. An interface element has been developed to model this behaviour and the element has been successfully implemented in the widely used geotechnical finite element programme PLAXIS.

Failure using interface elements in shear bands

Read more about: • Material instability and

development of slides • Progressive failure in soft clay

0 50 100 150 200 250 300 350Distance along clay layer (m)

τ 0

τ p

τ r

τ (x )

Earthquake analysis The computational model NonSSI (Non-linear Soil - Structure -Interaction) has been developed during the SIP. NonSSI improves the seismic analysis of structures. Material models for earthquake loading have also been developed.

Read more about: • Earthquake response analyses • Material model for earthquake

loading

Shear bands in a slope failure with strain softening material

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4.3 Consequence analysis

Slide run-out analysis Development of numerical models describing soil behaviour when a submarine slide is triggered has been given large emphasis in the SIP. The best practice method in geohazards slide risk assessment studies has been strengthened by using the computational fluid dynamics code CFX. This code is an enhanced tool for numerical simulation of mass flow. The code Different rheologic models for submarine slides were implemented in CFX. The strain-softening visco-plastic flow model reproduces a retrogressive sliding mechanism impressively well. The figure below

gives an example of results from a computational fluid dynamic analysis using the CFX code. The flow shows the formation of shear bands. Concentrated strain softening material may be observed together with wedges of nearly intact material.

ϕϕϕ

Physical slide flow model

Numerical simulation of a submarine slide in soft sensitive clay at different time steps after initial slide release (time increases from the top and downwards)

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Turbidity currents are an important mechanism in submarine mass transport. These currents are suspensions of sediment particles in turbulent water flow. Once developed, turbidity currents can flow independently from the originating mud/debris flow for long distances while entraining mass from the seafloor. A turbidity current material model has been implemented in CFX. Read more about: • Slide dynamics. Modelling tools • Erosion mechanisms • Slush flow model

Tsunami analysis Submarine slides may generate tsunamis with devastating effect in coastal areas. Tsunamis resulting from submarine mass movements are often modelled using a fixed shaped slide block as the source. However, submarine slides like the Storegga slide, develop during a continuous retrogressive process.

NGI has developed a model and a computer programme capable of calculating tsunami surface elevations caused by a variety of submarine slide sources, i.e. fixed shaped slides, deformable slides and retrogressive slides. This model has for example been used to model the earthquake that triggered the tsunami in the Indian Ocean 26 December 2004, and provided results very close to observations.

Read more about: • Tsunami analysis

Simulation of a slide moving as turbidity

Modell of tsunami in Indian Ocean, 26 December 2004

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Visualisation/GIS Different visualisation and GIS methods were investigated to facilitate and support evaluation of offshore hazards. Visualisation is a powerful tool to gain understanding of the problem and to provide answers. Visualisation of slides helps to simplify numerical analysis and improve the interpretation. Special visualisation modules have been used to show 3D geodata integrated with Geographical Information Systems (GIS). To be able to use such techniques data from site investigations must be stored in databases. Seabed or bathymetric have been used to show the location of borings, soundings and installations. Parameter variation of, for example water content and shear strength, has been illustrated by use of colour intensity scales (see figure). Snapshots of 3D models have been used to visualise interpreted soil layering and material parameters.

Read more about: • Visualisation of slides • GIS applications

Risk management The NORSOK Z-013 standard forms the basis for the best practice risk management developed by the SIP. A framework for integrated risk assessment including a glossary of terms has been established. Several case studies were used to illustrate and extend this framework. A risk assessment for offshore geohazards at Ormen Lange was presented in terms of the framework. Distribution functions for input parameters as well as uncertainties in soil properties and material behaviour have been evaluated. Read more about:

• Risk management

Combined presentation of historic records, simulation results and mitigation measures

Visualisation of geotechnical soil data by colouring scales

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4.4 Best practice NGI has used the results of the SIP to develop best practice guidelines for the assessment of offshore geohazards. The best practice is documented in a report and published as a WEB-site providing a dynamic tool that NGI intends to update continuously. The “Best practice WEB site” is available via the NGI home page: www.ngi.no 5 BENEFITS The SIP has contributed greatly to the understanding and assessment of offshore geohazards. The benefits include improvements in: • the understanding of seabed

instability mechanisms • the modelling of mass flow and

fluid and gas transport • the tools and methods for the

assessment of material properties and design parameters

• the quantification of uncertainties and frequency of geohazard events

• the assessment of the consequences of offshore geohazards

This new knowledge will enable a more rational assessment of geohazard risk and give valuable assistance for: • identification of geohazards • production of geohazard maps

and optimisation of field lay-out to minimise hazard and risk

• evaluation of measures to reduce risk of damage to wells, field installations and environment

NGI has used the results of the SIP to develop best practice guidelines for offshore geohazards

Reduced risk

fillingTmin

Ventingholes

Valve

Tmax

Valve opens and gas is released

V

Outlines of subsea bubble counter for monitoring leakage of free gas

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6 REFERENCES Papers, published presentations, lectures and reports on offshore geohazards produced during the SIP period 2002-2005 are listed. They were fully or partly financed by the SIP, or produced in connection with projects financed by NGIs clients in the oil and gas industry.

6.1 Published papers

Andresen, L., Jostad, H.P. (2002) Capacity analyses of anisotropic and strain-softening clays Proc. Num. Mod. Geomech.-NUMOG VIII, Rome, Italy, 2002, pp. 469-474 Andresen, L., Jostad, H.P. (2002) Numerical procedure for assessing the capacity of anisotropic and strain-softening clay. Proc. 5th World Congr. Comp. Mech.- WCCM V, Vienna, Austria, 2002, wccm.tuwien.ac.at Andresen, L.; Jostad, H.P. (2002) Undrained bearing capacity of anisotropic strain-softening clay Proc. 5th European Conf. Num. Meth. in Geotech. Eng.-NUMGE 2002, Paris, France, 2002. Andresen L. and Jostad, H.P. (2004). Modelling of shear band propagation in clays using interface elements with finite thickness. Proc. NGM 2004 - NUMOG IX, 2004, Ottawa, Canada, 2004. Andresen, L. and Jostad, H.P. (2004) Analyses of progressive failure in long natural slopes. Proc. Num. Mod. Geomech. - NUMOG IX, Ottawa, Canada, 2004. Berg, K., Solheim, A. and Bryn, P. (2005) The Pleistocene to recent geological development of the Ormen Lange area. Marine and Petroleum Geology. (Ormen Lange Special Issue) Vol. 22, No. 1/2, pp. 45-56.

Best, A.I., Clayton, C.R.I., Longva, O. and Szuman, M. (2003). The role of free gas in the activation of submarine slides in Finneidfjord. Submarine Mass Movements and Their Consequences, 1st International Symposium, Editors: Locat, Meinert and Boisvert, Kluwer Academic Publishers, pp. 491-498. Biscontin, G., Pestana, J.M. and Nadim, F. (2003). Seismic triggering of submarine slides in soft cohesive soil deposits. Marine Geology, (Special issue on landslide generated tsunamis) Vol. 203, No. 3/4, pp. 341-354. Bondevik, S., Løvholt, F., Harbitz, C.B., Mangerud, J., Dawson, A. and Svendsen, J.I. (2005) The Storegga slide tsunami - comparing field observations with numerical simulations. Marine and Petroleum Geology, (Ormen Lange Special Issue) Vol. 22, No. 1/2, pp. 195-208. Bryn, P., Solheim, A., Berg, K., Lien, R., Forsberg, C.F., Haflidason, H., Ottesen, D. and Rise, L. (2003). The Storegga slide complex: repeated large scale sliding in response to climatic cyclicity. In: Locat, J. and Mienert, J. (eds.). Submarine mass movements and their consequences, Nice, France, vol. 19, pp. 215-222. ISBN: 1-4020-1244-6. Bryn, P., Berg, K., Forsberg, C.F., Solheim, A. and Kvalstad, T.J. (2005) Explaining the Storegga slide. Marine and Petroleum Geology. (Ormen Lange Special Issue.) Vol. 22, No. 1/2, pp. 11-19

Bryn, P.; Berg, K.; Stoker, M.S.; Haflidason, H.; Solheim, A. (2005) Contourites and their relevance for mass wasting along the Mid-Norwegian margin. Marine and Petroleum Geology, (Ormen Lange Special Issue) Vol. 22, No. 1-2, pp. 85-96. Bøe R, L. Prøsch-Danielsen, A. Lepland, M. Høgestøl, P. Gauer and C.B. Harbitz (2006) A possible Early Holocene (ca. 10 000 - 9800/9700 14C yrs BP) slide-triggered tsunami at the Galta settlement sites, Rennesøy, SW Norway. Norwegian J. Geology (NGT). International Centre for Geohazards publ. no. 88.(in review). DeBlasio, F.V., Issler, D., Elvehøi, A., Harbitz, C.H., Ilstad, T., Bryn, P. and Lien, R. (2002) Dynamics and material properties of the gigant Storegga slide as suggested by numerical simulations Abstract to EG (Euro Graphics) 2002. DeBlasio, F.V., Issler, D., Elverhøi, A., Harbitz, C.B., Ilstad, T., Bryn, P., Lien, R. and Løvholt, F. (2003). Dynamics, velocity and run-out of the giant Storegga slide. Submarine Mass Movements and Their Consequences, Nice 2003. Proceedings, pp. 223-230. De Blasio, F.V., Ilstad, T., Elverhøi, A., Issler, D. and Harbitz, C.B. (2004) High mobility of subaqueous debris flows and the lubricating-layer model. Proceedings 2004 Offshore Technology Conference,

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Houston, Texas, 3-6 May 2004. OTC 16747, 11 pp. De Blasio, F., Engvik, L., Harbitz, C.B. and Elverhøi, A. (2004) Hydroplaning and Submarine Debris Flows. J. Geophys. Res., Oceans, Vol. 109, No. C1, C01002, doi:10.1029/2002JC001714 De Blasio, F., Elverhøi, A., Issler, D., Harbitz, C.B., Bryn, P. and Lien, R. (2004) Flow models of natural debris flows originating from over consolidated clay materials. Marine Geology, Vol. 213, No. 1/4, pp. 439–455, dio:10.1016/j.margeo.2004.10.018, EU Program COSTA Special Issue. De Blasio, F., Elverhøi, A., Issler, D., Harbitz, C.B., Bryn, P. and Lien, R. (2004) On the dynamics of subaqueous clay rich gravity mass flows - the giant Storegga slide. Marine and Petroleum Geology, (Ormen Lange Special Issue) Vol. 22, No. 1/2, pp. 179-186. Elverhøi, A., De Blasio, D., Butt, F.A., Issler, D., Harbitz, C.B., Engvik, L., Solheim, A. and Marr, J. (2003). Submarine mass-wasting on glacially influenced continental slopes — processes and dynamics. Proceedings, Geological Society of London, Special Publication, Vol. 203, pp. 73-87. Elverhøi, A., D. Issler, F. V. De Blasio, T. Ilstad, C.B. Harbitz and P. Gauer (2005) Emerging insights on the dynamics of submarine debris flows. Natural Hazards and Earth System Sciences, 5, 633–648. SRef-ID: 1684-9981/nhess/2005-5-633, European Geosciences Union. International Centre for Geohazards publ. no. 90. Forsberg, C.F. and Locat, J. (2004) Sedimentation in the Storegga region, offshore Norway as seen from mineralogical and microfabic analyses. Journal Marine and

Petroleum Geology. Special Ormen Lange issue. Forsberg, C.F. and Locat, J. (2005) Mineralogical and micro structural development of the sediments on the Mid-Norwegian margin.. Marine and Petroleum Geology. (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 109-122. Gauer, P. (2002) The use of a numerical snowdrift model as a decision making tool in the planning of avalanche protection measures International Snow Science Workshop. Penticon, B.C. Canada 2002. Proceedings, pp. 604-607. Gauer, P. and Issler, D. (2004) Possible erosion mechanisms in snow avalanches Annals of Glaciology, Vol. 38, pp. 384-392. Gauer, P., Kvalstad, T. J., Forsberg, C. F., Bryn, P. and Berg, K. (2005) The Last Phase of the Storegga Slide: Simulation of Retrogressive Slide Dynamics and Comparison with SlideScar Morphology. Marine Petroleum and Geology, (Ormen Lange Special Iissue) Vol. 22, No. 1/2, pp. 171-178. Glimsdal, S., G.K. Pedersen, K Atakan, C.B. Harbitz, H.P. Langtangen and F. Løvholt, F. (2004) Propagation of the Dec. 26 2004 Indian Ocean Tsunami: effects of dispersion and source characteristics. Accepted for publication in Int. J. of Fluid Mech. Research. Grozic, J.L.H., Lunne, T. and Pande, S. (2003). An oedometer test study on the preconsolidation stress of glaciomarine clays. Canadian Geotechnical Journal, Vol.. 40, No. 5, pp. 857-872. Grozic, J.L.H., Lunne, T. and Pande, S. (2004) Reply to discussion by R.V. Clementino on ‘An oedometer test study on the preconsolidation stress of glaciomarine clays’.

Canadian Geotechnical Journal, Vol. 42, No. 3, pp. 975-976. Haflidason, H., Lien, R., Sejrup, H.P., Forsberg, C.F. and Bryn, P. (2005). The dating and morphometry of the Storegga slide. Marine and Petroleum Geology, (Ormen Lange Special Issue). Vol. 22, No. 1/2, pp. 123-136. Haflidason, H., Sejrup, H.P., Hjelstuen, B.O., Nygård, A., Mienert, J., Bryn, P., Lien, R., Forsberg, C.F., Berg, K. and Masson, D. (2004) The Storegga slide: architecture, geometry and slide development. Marine Geology, Vol. 213, No. 1-4, pp. 201-234. Hanzawa,H. N. Nutt, T. Lunne, Y.X. Tang and M. Long (2005) A comparative study between the NGI direct simple shear apparatus and the Mikasa direct shear apparatus. Submitted for possible publication in Soils and Foundations. Harbitz, C.B., Parker, G., Elverhøi, A., Marr, J.G., Mohrig, D. and Harff, P.A. (2003). Hydroplaning of subaqueous debris flows and glide blocks: Analytical solutions and discussion. Journal Geophysical Research, 108(B7), paper 2349, doi:10.1029/2001JB001454 Haugen, K.B., Løvholt, F. and Harbitz, C.B. (2005) Fundamental mechanisms for tsunami generation by submarine mass flows in idealised geometries. Marine and Petroleum Geology. (Ormen Lange Special Issue) Vol. 22, No. 1/2, pp. 209-217. Ilstad, T., De Blasio, F.V., Elverhøi, A., Harbitz, C.B., Engvik, L., Longva, O. and Marr, J.G. (2004) On the frontal dynamics and morphology of submarine debris flows. Marine Geology, Vol. 213, No. 1/4, pp. 481–497, doi:10.1016/j.margeo.2004.10.020, EU Program COSTA Special Issue.

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Ilstad, T., Marr, J.G., Elverhøi, A. and Harbitz, C.B. (2004) Laboratory studies of subaqueous debris flows by measurements of pore-fluid pressure and total stress. Marine Geology, Vol. 213, No. 1/4,403–414, dio:10.1016/ j.margeo.2004.10.016, EU Program COSTA Special Issue. Issler, D., De Blasio, F.V., Elverhøi, A., Bryn, P. and Lien, (2005). Scaling behaviour of clay-rich submarine debris flows. Marine Petroleum Geology, (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 187-194. Jaedicke, C. (2003) Climate database for avalanche warning in Norway. International Young Geotechnical Engineers' Conference, 2. Constantza - Mamaia, Romania 2003. Proceedings, Vol. 87-88. Submitted for publ. in: Cold Regions Science and Technology. Kvalstad, T.J., F. Nadim, A. Kaynia, K.H. Mokkelbost and P. Bryn (2005). Soil conditions and slope stability in the Ormen Lange area. Marine and Petroleum Geology, (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 299-310. Kvalstad, T.J., Andresen, L., Forsberg, C.F., Berg, K. and Bryn, P. (2005) The Storegga Slide: Evaluation of triggering sources and slide mechanisms. Marine and Petroleum Geology. (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 245-256. Kvalstad, T.J., Nadim, F., Kaynia, A.M., Mokkelbost, K.H. and Bryn, P. (2005) Soil conditions and slope stability in the Ormen Lange area. Marine and Petroleum Geology. (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 299-310.

Lacasse, S. (2002) 37th Terzaghi Lecture: Geotechnical Solutions for the Offshore: Synergy of Research and Practice. ASCE National Convention 2001, Houston, October 2001. To be published in ASCE Journal of Geotechnical and Environmental Engineering (review process) Also publ in: Offshore Site Investigation and Geotechnics; Diversity and Sustainability. Proceedings of an International Conference, London 2002. Pp. 13-20. Lacasse, S. (2002) Safety and hazards. Keynote Lecture. International Conference on Innovation and Sustainable Development of Civil Engineering in the 21st Century. Beijing, China. 1-3 August 2002. Proceedings, p. K11-K16. Lunne, T., Berre, T., Andersen, K.H., Strandvik, S. and Sjursen, M. (2004) Effects of sample disturbance and consolidation procedures on measured shear strength of soft marine Norwegian clays. Canadian Geotechnical Journal, 65. Lunne,T.,M. F. Randolph,M.F., S. F. Chung, K.H. Andersen, K.H. and M. Sjursen (2005) Comparison of cone and T-bar factors in two onshore and one offshore clay sediments. Proceedings of International Symposium on Frontiers on Geotechnics; pp. 981-991. Perth, Australia, Sept. 2005. Lunne, T. and Long, M. (2006) Review of long seabed samplers and criteria for new sampler design. Accepted for publication in Marine Geology. Lunne,T., T. Berre, K. H. Andersen, S. Strandvik and M. Sjursen (2006) Effects of sample disturbance and consolidation procedures on measured shear strength of soft marine Norwegian clays. Accepted for publication in Canadian Geotechnical Journal.

Løvholt, F., Harbitz, C.B. and Haugen, K.B. (2005) A parametric study of tsunamis generated by submarine slides in the Ormen Lange/ Storegga area off western Norway. Marine and Petroleum Geology, (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 219-231. Marr, J.G., A. Elverhøi, C.B. Harbitz, J. Imran, P. Harff (2002). Numerical simulation of mud-rich subaqueous debris flows on the glacially active margins of the Svalbard-Barents Sea. Marine Geology, Vol. 188, No. 3/4, pp. 351-364. Nadim, F. (2002) Probabilsitic methods for geohazard problems: State-of-the-Art. Proc., Probabilistics in GeoTechnics Conference, Graz, Austria, 15-19 Sept, 2002. Pp. 333-350 Nadim, F., Kvalstad, T.J., and Guttormsen, T. (2005) Quantification of risks associated with seabed instability at Ormen Lange. Marine and Petroleum Geology, (Ormen Lange Special Issue) Vol. 22, No. 1/2, pp. 311-318. Powell, J.J.M. and T. Lunne (2005) A comparison of different sized piezocones in UK clays. International Conference on Soil Mechanics and Foundation Engineering, 16. Osaka 2005. Proceedings, Vol. 2, pp. 531-536. Solheim, A., Berg, K., Forsberg, C.F. and Bryn, P. (2005) The Storegga Slide complex: Repetitive large scale sliding with similar cause and development. Marine and Petroleum Geology. (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 97-107

Published papers

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Solheim, A., Bryn, P., Sejrup, H.P., Mienert, J. and Berg, K. (Editors) (2004). Ormen Lange – an integrated study for the safe development of a deep-water gas field within the Storegga Slide Complex, NE Atlantic continental margin. Marine and Petroleum Geology, Ormen Lange Special issue. A collection of 15 reviewed articles. Solheim, A., R. Bhasin, F.V. De Blasio, L.H. Blikra, S. Boyle, A. Braaten, J. Dehls,

A. Elverhøi, B. Etzelmüller, S. Glimsdal, C.B. Harbitz, H. Heyerdahl, Ø.A. Høydahl, H. Iwe, K. Karlsrud, S. Lacasse, I. Lecomte, C. Lindholm, O. Longva, F. Løvholt, F. Nadim, S. Nordal, B. Romstad, J.K. Røed, and J.M. Strout (2005). International Centre for Geohazards (ICG): Assessment, prevention and mitigation of geohazards. Norwegian Journal of Geology, No. 1/2, Vol. 85, 45-62. International Centre for Geohazards publ. no. 68.

Strout, J.M. and Tjelta, T.I. (2005) In situ pore pressures: What is their significance and how can they be reliably measured? Marine and Petroleum Geology, (Ormen Lange Special Issue), Vol. 22, No. 1/2, pp. 275-285. Yang S L., T. Kvalstad, A.Solheim , C.F.Forsberg (2006) Parameter studies of sediments involved in the Storegga Slide. Geo-Marine Letters (In press).

6.2 Published lectures and presentations Andersen, E.S., Solheim, A., Tjelta, T.I., Sætre, H.J., Hansch, K., Austin, T.J.F., Clark, J., Jenssen, A., Johansen (2005) The NDP Seabed Project: Mapping of Geo-hazards along the Mid-Norwegian Continental Margin. 2nd Int.Conf Submarine mass movements, Holmenkollen, Oslo, Norway, 7-9 September 2005. Andresen, L., Jostad, H.P. (2002) Capacity analysis of anisotropic and strain-softening clays NUMOG VIII/April 2002/Rome, Italy Andresen, L., Jostad, H.P. (2002) Numerical Procedure for Assessing the Capacity of Anisotropic and Strain-Softening Clay5th World Congress Computational Mechanics, WCCM V/July 2002/ Vienna, Austria Andresen, L., Jostad, H.P. (2002) Undrained Bearing Capacity of Anisotropic Strain-Softening Clay5th European Conference on Numerical Methods in Geotechnical Engineering.NUMGE/September 2002/Paris, France Andresen, L. (2001) Submarine Slide Initiation and Retrogressive Spreading – Storegga Slide Case study, NGI report 521001-10.

Andresen, L. and Jostad, H.P. (2004) Janbu's Modulus Concept vs. Plaxis Soft Soil Model Proc. NGM 2004 - XIV Nordic Geotechnical Meeting Vol-1, Ystad, Sweden. Andresen, L. (2004) The role of progressive failure in landslide-mechanisms. University of Massachusetts- geotechnical Eng., Amherst, USA 23 Aug. 2004 Bondevik, S., Harbitz, C.B., Løvholt, F., Dawson, A., Dawson, S., Mangerud, J. and Svendsen, J.I. (2002) The Storegga Slide tsunami along the Norwegian coast - from the geological record to numerical simulations NPF konferansen: Onshore - offshore relationships on the North Atlantic Margin, 7.-9. October (postponed from May), 2002/Trondheim, Norway Bryn, P, Kvalstad, T.J., Guttormsen, T.R., Kjærnes, P.A., Lund, J. Nadim, F. and Olsen, J. (2004) Storegga Slide Risk Assessment. OTC Paper 16560, 2004 Offshore Technology Conference, Houston, Texas. Cuisiat, F., Kvalstad, T.J. and Skjærstein A. (2003). Evaluation of subsidence effects on slope stability due to production from a

deep-water gas field within the Storegga Slide Complex, NE Atlantic continental margin. 3rd FLAC Symposium on Numerical Modelling in Geomechanics. Sudbury, Canada. De Blasio, F.V., Issler, D., Elverhøi, A., Harbitz, C.B., Ilstad, T., Bryn, P. and Lien, R. (2003). Dynamics and material properties of the giant Storegga slide as suggested by numerical simulations. NGF Abstracts and Proceedings, No. 1 (Norsk geologisk forening.). DiBiagio, E. (2004) Geotechnical and structural instrumentaiton in the marine environment. Invited Lecture, 1 Congreso Nation, Geotecnia Y Medio Ambiente, Asociacion Tecnica de Puertos y Costas, Huelva, Spain. De Blasio, F., Issler, D., Elverhøi, A., Harbitz, C.B., Ilstad, T., Bryn, P., Lien, R. and Løvholt, F. (2004) Dynamics, Velocity and Run-out of the Giant Storegga Slide. EGS-AGU-EUG Joint Assembly, Nice, France.

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Elverhøi, A. and Issler, D. (2004) Assessment of gravity mass flow hazard in the Ormen Lange area. Invited lecture in the course on Mitigation of landslides and other gravity mass flow hazards, University of Oslo (Norway), October 2004. Elverhøi, A., De Blasio, F.V., Engvik, L., Issler, D., Nystuen, J.P., Ilstad, T., Harbitz, C., Gauer, P. (2005) Understanding the high mobility of subaqueous debris flows. 2nd Int.Conf Submarine mass movements, Holmenkollen, Oslo, Norway, 7-9 September 2005. Gauer, P. (2002) The use of a numerical snow-drift model as a decision making tool in the planning of avalanche protection measures ISSW (International Snow Science Workshop) 2002, 29 Sept-4 Oct 2002/Penticon, British Colombia, Canada Gauer, P (2003). Possible Erosion Mechanisms in Snow Avalanches International Symposium on Snow and Avalanches Davos, Switzerland. Gauer, P. (2003). Possible Erosion Mechanisms in Snow Avalanches Isaac Newton Institute Workshop on Geophysical Granular and Particle-Laden Flows Bristol, United Kingdom. Gauer, P. (2004) Numerical modeling of a slush-flow event. Proceedings of the International Snow Science Workshop 2004, Jackson Hole, Wyoming, United States. Gauer, P., Elverhøi, A., De Blasio, F.V. (2005) On numerical simulations of subaqueous slides: Back-calculations of laboratory experiments. 2nd Int.Conf Submarine mass movements, Holmenkollen, Oslo, Norway, 7-9 September 2005.

Grozic, J. (2003). Gas hydrates and submarine slope instability. Geohazards 2003, Edmonton, Canada, June 2003, pp 143-150, ISBN 0-920505-23-6. Harbitz, C.B., Pedersen, G., Løvholt, F. Haugen, K.B., Glimsdal, S. (2005) KEYNOTE: Mechanisms of slide generated tsunamis. 2nd Int.Conf Submarine mass movements, Holmenkollen, Oslo, Norway, 7-9 September 2005. Issler, D., De Blasio, F.V., Elverhøi, A., Ilstad, T., Haflidason, H., Bryn, P. and Lien, R. (2004) Issues in the assessment of gravity mass flow hazard in the Storegga area off the western Norwegian coast. In: J. Locat and J. Mienert (eds.), Submarine Mass Movements and Their Consequences. Advances in Natural and Technological Hazards Research, vol. 19. Kluwer Academic Publishers, Dordrecht (Netherlands). Pages 221–230. Jaedicke, C. (2004) Climate database for avalanche warning in Norway. ISSW 2004, Teton Village, USA. Jostad, H.P. (2004) Modelling of shear band propagation in clay using interface elements with finite thickness. University of Massachusetts - Geotechnical Engineering , Amherst, USA, 23 August 2004. Jostad, H.P, T. Vikas Thakur and L. Andresen. (2006) Calculation of shear band thickness in sensituive clays. Sixth European conference on numerical methods in geotechnical engineering, Graz, 2006 (in press). Karlsrud, K. (2005) Strategi for gjenoppbygging I Thailand etter tsunamien 26. desember, 2004. Fjellsprengnings-teknikk, bergmekanikk/geoteknikk 2005.

Karlsrud, K., H. Bungum, C.H Harbitz, F. Løvholt, B.V. Vangelsten and S. Glimsdal, S. (2005). Strategy for re-construction in Thailand following the 26 December 2004 tsunami event. In: Chu, Phoon and Yong (eds): International Conference on Geotechnical Engineering for Disaster Mitigation & Rehabilitation. World Scientific Publishing Company ISBN 981-256-469-1. Kvalstad, T.J., Nadim, F. (2002) Risk Assessment of Ocean Margins NPF konferansen: Onshore - offshore relationships on the North Atlantic Margin, 7.-9. October (postphoned from May), 2002/Trondheim, Norway Kvalstad, T.J. (2002) Slope Stability at Ormen Lange SUT International Site Investigation Conference; Offshore Site Investigation and Geotechnics - Diversity and Sustainability, London in November 2002 Kvalstad, T.J. (2003) Ormen Lange gas field: Slope stability and pipelines in the Storegga slide scar. Invited Paper, Workshop on "Landslides and lifelines - submarine landslides affecting pipelines, lifelines in slow moving slides and in areas prone to debris-flow events", IX International Symposium on Landslides, Rio de Janeiro, Brazil. Kvalstad, T.J. (2004) Ormen Lange gas field: Slope stability and pipelines in the Storegga slide scar. Invited lecture, Workshop on "Landslides and lifelines - submarine landslides affecting pipelines, lifelines in slow moving slides and in areas prone to debris-flow events". IX International Symposium on Landslides, Rio de Janeiro, Brazil, 26 June, 2004. Kvalstad, T.J. (2005) Energy model for evaluation of retrogressive slide potential and slide dynamics on continental

Published lectures and presentations

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slopes. 2nd Int.Conf Submarine mass movements, Holmenkollen, Oslo, Norway, 7-9 September 2005. Lacasse, S. (2002) 37th Terzaghi Lecture: Geotechnical Solutions for the Offshore: Synergy of Reseach and Practice. The lecture is an award and was repeated in 15 cities/2002/ Houston, Orlando, Oslo, Trondheim, Paris, San Francisco, Ohio, Seattle, Portland, Vancouver, Colbye Station, Amherst (MA), Boston, Chicago, Winnipeg, Hong Kong Lacasse, S. and Nadim, F (2003). Reliability Analysis - Reliability and Risk in geo-Engineering. Keynote Lecture. Intern. Workshop on Dam Foundation and Tunnelling in Weak Rocks.Paper 1 New Delhi, India. Lacasse, S. (2002) Safety and hazards. Keynote Lecture. International Conference on Innovation and Sustainable Development of Civil in the 21st Century Engineering/1-3 August 2002/Beijing, China. Lacasse, S., Nadim, F. and Høeg, K. (2003). Risk Assessment in Soil and Rock Engineering. PanAm Conference, SARA, MIT, Cambridge, Mass., USA. Lacasse, S. (2004) Risk Assessment for Geotechnical Solutions Offshore. Keynote Paper. OMAE2004-51144. Proc. OMAE 2004, 23rd International Conference on Offshore Mechanics and Arctic Engineering. Vancouver, Canada. June 2004. Lacasse, S., Solheim, A. and Nadim, F. (2003). Understanding Geohazards. EAGE 2004 Stavanger Lunne, T. and Schjetne, K. (2003).

Geotechnical aspects of deepwater field development. Petrotech, New Delhi. Lunne, T. and Sjursen, M. (2003). Sample disturbance effects in soft Norwegian clays. Sampling disturbance effects. University College Dublin. Lunne, T., Long, M. and Forsberg, C.F. (2003). Characterization and engineering properties of Onsøy clay. Soil Characterization, Singapore, Vol I, pp. 395-428. Lunne, T., Long, M. and Forsberg, C.F. (2003). Characterization and engineering properties of Holmen, Drammen sand. Soil Characterization, Singapore, Vol II, pp. 1121-1148. Lunne, T. and Schjetne, K. (2004) Geotechnical input to deepwater field development. Keynote Lecture, Arctic Conference, Murmansk, Nov. 2004. Løvholt, F., Harbitz, C.B. (2005) Slope Stability Assessment in the Ormen Lange Field - Extended Tsunami Analyses, NGI report 19993016-16, (rev 1 in progress) Løvholt, F., Harbitz, C.B. (2002) Reservoir Rim Stability Study, San Roque – Rockslide Generated Water Waves, NGI report 20021147-2 Løvholt, F., Harbitz, C.B. Tsunamis generated by rockslides in Geiranger and Tafjorden, scenarios and model comparisons (in progress) Løvholt, F., Harbitz, C.B. and Haugen, K.B. (2004). Tsunami generation from retrogressive submarine slides in the Storegga/Ormen Lange area, 32nd International Geological Conference - Firenze 2004.

Masson, D. G., Harbitz, C. B., Wynn, R. B., Pedersen G., and Løvholt, F. (in review, 2006) Submarine landslides – processes, triggers and hazard prediction. Submitted for publication in Philosophical Transactors of the Royal Society. Nadim, F. (2002) Probabilsitic methods for geohazard problems: State-of-the-Art lecture. Probabilistics in GeoTechnics Conference, Graz, Austria, 15-19 Sept, 2002. Nadim, F. and Lacasse, S. (2003). Probabilistic methods for quantification and mapping of geohazards. 3rd Canadian Conference on Geotechnique and Natural Hazards, Emonton, Canada, pp. 279-286. Conference Preprints, ISBN 0-920505-23-6 Nadim, F., Krunic, D. and Jeanjean, P. (2003). Probabilistic slope stability analyses of the Sigsbee Escarpment Proceedings, OTC 15203, Offshore Technology Conference ’03, Houston, Texas, May 2003. Nadim, F., Kvalstad, T.J. and Guttormsen, T. (2004) Quantification of risks associated with seabed instability at Ormen Lange. 2004 OTC Offshore Technology Conference, Houston, Texas. Nadim, F. (2005) KEYNOTE: Challenges to geo-scientists in risk assessment for submarine slides. 2nd Int.Conf Submarine mass movements, Holmenkollen, Oslo, Norway, 7-9 September 2005. Nowacki, F., Solhjell, E., Nadim F., Liedke E., Andersen, K.H. and Andresen, L. (2003). Deterministic Slope Stability Analyses of the Sigsbee Escarpment. Proceedings, OTC 15160, Offshore Technology Conference ’03, Houston, Texas.

Published lectures and presentations

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Rise, L., Ottesen, D., Longva, O., Solheim, A., Andersen, E.S. andAyers, S. (2005) The Sklinnadjupet Slide and its relation to the great impact of the third last glaciation on the mid-Norwegian margin. 2nd. International Conference on Submarine Mass Movements and Their Consequences., Oslo September 5-7, 2005. Schnellmann, M., A. Solheim, C.F. Forsberg, I. Lecomte, T.J. Kvalstad and S. Yang (2005) Identifying weak layers and potential slip planes by integrating amplitude versus offset (AVO) analyses and post-stack seismic attributes. 2nd. International Conference on Submarine Mass Movements and Their Consequences., Oslo September 5-7, 2005. SINTEF (2004) Brukerkravinnhenting for NGIs datatflyt-prosjekt. Rapport fra SINTEF IKT. Rapport nr SFT90 F04005, January 2004 Solheim, A., Bryn, P., Sejrup, H.P., Mienert, J., Berg, K. (2003). Ormen Lange – an integrated study for the safe development of a deep-water gas field within the Storegga Slide Complex, NE Atlantic continental margin. A collection of 15 refereed articles. Marine and Petroleum Geology, Ormen Lange Special Issue. Solheim, A. and F. Nadim (2003) International Centre for Geohazards (ICG) established at the Norwegian Geotechnical Institute (NGI) (Focus on offshore geohazards). Ocean Margin Research Conference, Paris, September 15-17, 2003. Poster. Solheim, A., F. Nadim and L.H. Blikra (2003) International Centre for Geohazards (ICG) established at the Norwegian Geotechnical Institute (NGI) (Focus on rockslides and tsunamis).

American Geophysical Union, San Francisco, December 8-12, 2003. Paper no. OS22B-1164.- Poster. Eos. Trans. AGU, 84(46), Fall Meet. Suppl., Abstract , 2003. Solheim, A. and C.F.F Forsberg (2003) The need for integrated geo-studies in offshore site investigations. Lecture given at “International Soil Investigation Forum”, Annual Meeting, Oslo, Dec. 2003. Solheim, A (2004) Main achievements of the Seabed Project offshore mid-Norway, 1995-2004. The Seabed Project, Partner meeting, Lyseby, Oslo, August 26, 2004. Solheim, A., Forsberg, C.F., Kvalstad, T.J., Harbitz, C.B., Nadim, F. and Yang, S. (2004) Submarine slides in high latitudes – integrating geotechnical data with other geo-data and numerical modelling. Invited Lecture, 2nd Euromargins Conference. Barcelona, Spain, 11-13 November, 2004. Solheim, A. and Bryn, P. (2004) The Ormen Lange Project: A necessary assessment of geohazards in relation to the development of a deep-water gas field. Keynote lecture at the conference "Ireland at Risk", Dublin Castle, 4 October 2004 Solheim, A., Forsberg, C.F., Kvalstad, T.J., Harbitz, C.B., Nadim, F. and Yang, S. (2004) Submarine slides in high latitudes – integrating geotechnical data with other geo-data and numerical modelling. 2nd Euromargins Conference. Barcelona, Spain, 11-13 November, 2004. Solheim, A., Bhasin, R., De Blasio, F.V, Blikra, L.H., Boyle, S., Braathen, A., Dehls, J., Elverhøi, A, Etzelmüller B., Glimsdal, S., Harbitz, C.B., Heyerdahl, H., Høydahl, Ø.A., Iwe, H., Karlsrud, K., Lacasse, S.,

LeComte, I., Lindholm, C., Longva, O., Løvholt, F., Nadim, F., Nordal, S., Romstad, B., Røed, J.K. Strout, J.M.S.(2005) Research on assessment, prevention and mitigation of geohazards at the International Centre for Geohazards (ICG). Norwegian Geological Winter Conference, Røros, Norway, 7-10 January, 2005. Solheim, A., D. A. Long, and J. Mienert (2005) Large slides and geohazards on the Norwegian Continental Margin. “Ice and Environmental Change around the Norwegian – Greenland Sea; A Nansen seminar in celebration of 100 years of Norwegian Independence”. Scott Polar Research Institute, University of Cambridge, 19. October, 2005. (Invited lecture) Strout, J. M. (2005) Capabilities NGI/ICG geohazards. Workshop NORAD 21 January 2005. Strout, J.M. and Mokkelbost, K.H: (2003). Pushing the envelope in subsea slope stability analysis: novel in situ and laboratory tests at Ormen Lange field. Strout, J., Longva, O. (2005) The Finnefjord experiment. 2nd Int.Conf Submarine mass movements, Holmenkollen, Oslo, Norway, 7-9 September 2005. Yang, S., A. Solheim, T.J. Kvalstad, C.F. Forsberg, and M. Schnellmann (2005) 2nd. International Conference on Submarine Mass Movements and Their Consequences, Oslo September 5-7, 2005. Conference committees: Solheim, A., Kvalstad, T.J., Forsberg, C.F., Tjelta, T.I., Elverhøi, A., Mienert, J., Bryn, P., and Locat, J., 2005: 2nd. International Conference on Submarine Mass Movements and Their Consequences, Oslo September 5-7, 2005.

Published lectures and presentations

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Editorial Committees: Solheim, A.., Bryn, P., Sejrup, H.P., Mienert, J., Berg, K. (Editors): Ormen Lange – an integrated study for the safe development of a deep-water gas field within the Storegga Slide Complex, NE Atlantic continental margin. Marine and Petroleum Geology, Vol. 22, Nos. 1-2.

Martinsen, O., Hadler-Jacobsen, F., Solheim, A., and Posamentier, H. (Editors), in preparation: Deep-water sedimentary systems of Arctic and North Atlantic Margins. Proc. Of International Conference, Stavanger, 18-20 October, 2004. Proceedings. Norwegian Journal of Geology.

Solheim, A., Kvalstad, T.J., Forsberg, C.F., Tjelta, T.I., Elverhøi, A., Mienert, J., Bryn, P., and Locat, J., in preparation: 2nd. International Conference on Submarine Mass Movements and Their Consequences., Oslo September 5-7, 2005, Proceedings. Norwegian Journal of Geology.

6.3 NGI-reports

2002 NGI-report 20021239-1 Geotechnical Optimisation of Seabed Sampler. Criteria for Sampler Design, 21 October 2002. NGI-report 20021023-13, Real-time monitoring: Contactless serial interface, 19 December 2002. 2003 NGI-report 20021023-32, Tsunami-studies, 6 February 2003. NGI-report 20021049-1, Development of user interfaces in MATLAB. Example studies, 7 January 2003. NGI-report 20021023-16, Metode for feltovervåkning med bruk av databaseverktøy og GIS, 12 February 2003. NGI-report 20021023-12, Database for laboratoriedata, 1 July 2003. NGI-report 20021023-18, Geophysical methods. Shallow water flow – a literature survey, 30 September 2003. NGI-report 20021023-17, Suction in clay samples, 7 October 2003. NGI-report 20021023-34, Validity of Turbidity Current Model, 1 December 2003.

NGI-report 20021023-33, Overall slide processes: Possible erosion mechanisms, 17 December 2003. NGI-report 20021023-31, Establishment of CFX, 22 December 2003. 2004 NGI-report 20021023-22, Using PLAXIS to perform sedimentation analysis, 1 January 2004. 20021023. Multilevel piezometer technical documentation. Technical note dated 27 January 2004. 20021023. Small diameter data logger. Technical Note dated 27 January 2004. GIS i forbindelse med offshore grunnundersøkelser – forstudie. Technical note dated 19 February 2004 NGI-report 20021239-2, Geotechnical Optimisation of Seabed Sampler. Detailed Criteria of New Sampler and Plans for Testing Out Prototype, 5 March 2004 NGI-report 20031091-3, Risk and vulnerability for geohazards. Vulnerability in Relation to Risk Management of Natural Hazards, 8 August 2004.

NGI-report 20031091-2, Risk and vulnerability for geohazard. Hazard and risk scoring of quick clay slides in Norway – a probabilistic perspective, 22 September 2004. NGI-report 20031091-1, Risk and vulnerability for geohazards. Glossary of risk assessment terms, 30 September 2004. NGI-report 20031091-4, Risk and vulnerability for geohazards. General non-Gaussian probability models for first-order reliability method (FORM). A State-of-the-Art report, 30 September 2004. NGI-report 20021023-35, Feasibility study for a slushflow model within CFX4, 8 December 2004. 2005 20041046. Skred- og klimadatabase. Technical note dated 7 January 2005. NGI-report 20021023-20, Informasjonssystem for dataflyt i forbindelse med laboratorietjenester. Systemspesifikasjon, 10 January 2005. NGI-report 20021023-27, EM and gas hydrates, 21 January 2005. NGI-report 20031091-5, Risk and vulnerability for geohazards. Slope stability analysis for risk assessment, 31 January 2005.

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NGI-report 20021023-14, Suction in clay samples – measurements on soft clay, 18 March 2005. NGI-report 20021023-36, 3D Visualisation of slides and the NIS slide model, 31 March 2005 NGI-report 20021023-23, Measurement of remoulded undrained shear strength – literature survey, 31 March 2005. NGI-report 20051073-1, Grunn gass instrumentering - Semikvantitativ måling av gass fra seeps ved hjelp av SPMD, 1 June 2005 NGI-report 20021023-26 Seabed Seismic Source – Shallow Applications: Source –Seabed Coupling, 2 June 2005. NGI-report 20021023-10, Correction methods for oedometer tests. User's Guide, Version 1.00, 15 August 2005 NGI-report 20021023-11, Correction methods for oedometer tests. Theory and verification, 15 August 2005. NGI-report 20021023-29, The potential of post-stack and Amplitude versus Offset (AVO) analyses for identification of weak layers, 16 September 2005 NGI-report 20021023-38, NGI-ANI2 Material Model – User defined material model for PLAXIS Version 8.x – User Manual, 21 September 2005 NGI-report 20051060-1, Generalised Integrated Risk Assessment Framework, 30 September 2005 NGI-report 20051060-3, Vulnerability in Context of Risk Management for Natural Hazards, 30 September 2005

NGI-report 20051060-4, Earthquake hazard, vulnerability and risk State-of-the-art in Seismic Hazard Analysis with Emphasis on Ground Motion Models, 30 September 2005 NGI-report 20021023-24. Specific correlations between index parameters and soil design parameters. Caspian Sea soil, 10 October 2005 NGI-report 20021023-15, Real time monitoring: Benchmark review and calculations, 16 November 2005. NGI-report 20021023-25, Subsea instrumentation “Best practice”. Practical measures to improve reliability of subsea instrumentation systems, 22 November 2005 20021023. Development of a sediment database for offshore geohazard areas. Technical note dated 28 November 2005 20021023. Experiment to evaluate pore pressure caused by salinity gradients in poorly consolidated sediments. Technical note dated 28 November 2005. NGI-report 20051073-2, Shallow Gas Instrument- ation - Self-expanding pipe plug for shallow gas collection, 2 December 2005 NGI-report 20051073-3, Shallow Gas Instrumentation - System for collection and measurement of gas flux, 2 December 2005 NGI-report 20021023-2, Offshore geohazards. Stratigic institute programme. Summary report, 8 December 2005

NGI-report 20021023-37, User's Guide to FEM earthquake response software NONSSI, 12 December 2005 NGI-report 20021023-3, Gas related to offshore geohazard, 22 December 2005 NGI-report 20021023-4, Measurement of remoulded shear strength - comparison of results from various tests in a range of clays, 28 December 2005 NGI-report 20021239-3, Geotechnical Optimisation of Seabed Sampler. Phase 3: Special CPT sleeve tests and testing out prototype sampler, 28 December 2005. NGI-report 20021023-19, Use of shear waves to detect overpressured zones, 30 December 2005 NGI-report 20021023-39, Cyclic behaviour of cohesionless soil earthquake analyses, 30 December 2005. NGI-report 20021023-28, Treating seismic reflection data in offshore geohazard studies at NGI: Workflow, software tools and practical advice, 30 December 2005. NGI-report 20051060-5, Acceptable and tolerable Risk – a Literature Review, 30 December 2005 NGI-report 20021023-21, Modellering av raskanter med PLAXIS, 31 desember 2005 NGI-report 20021023-30, Best practice. Offshore geohazards, 31 December 2005

NGI-reports

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6.4 Press and media coverage Forskning 5/02, ”Til kamp mot naturkatastrofene”, Bjarne Røsjø, NGI Teknisk Ukeblad 13/02, ”Prioritering må til”, Suzanne Lacasse Geo Sept/02, ”Ny giv for norsk geo-forskning”, Halfdan Carstens, GEO (Kjell Hauge) Teknisk Ukeblad 45/02, ”Skredfaren over”, Linda Hårvik og Tore J. Kvalstad Bistandsaktuelt 02/03, ”Norsk forskning mot naturkatastrofer”, Oddvar Kjekstad and Kjell Hauge GEO, December, 2003. ”Geologisk kunnskap redder liv”, Kristen Mørk,GEO (Farrokh Nadim) Byggeindustrien, 12/03.”Risikodemperen”, Jan-Gunnar Fjeldstad, Byggeindustrien (Suzanne Lacasse and Kjell Hauge) Teknisk Ukeblad 30/03, ”Forskning under press", Veslemøy Nestvold, TU (Suzanne Lacasse) Teknisk Ukeblad 31/03, ”Eksperter på naturkatastrofer”, Veslemøy

Nestvold, TU (Farrokh Nadim) New Science, 24 January 2004, ”Scoting on a wet bottom: Some undersea landslides ride a nearly frictionless slick of water”, Sid Perkins Dagbladet 20 September 2004, "Naturkatastrofer - en global utfordring", Farrokh Nadim and Suzanne Lacasse Appolon, University of Oslo, 03/2004. “Da flodbølgen slukte Nord-Vestlandet”, Yngve Vogt, Apollon (Finn Løvholt) Dagbladet, 19 October 2004, ”Monsterbølgen slukte Vestlandet”, Sigbjørn Strand, Dagbladet (Finn Løvholt) Aftenposten, 4 January 2005. ”Flodbølger kan de varsles?”, Bjørn Gjevik and Geir Pedersen, UiO and Carl Harbitz Forskning 3/05. “Halve befolkninga på jorda er utsett for naturkatastrofar", Bjarne Røsjø, NGI

Byggeindindustrien. 3/05. “Viktig med strakstiltak”, Anne Beth Jensen, Byggeindustrien (Kjell Karlsrud) Bistandsaktuelt. 1/2005. ”UD og Norad kartlegger norsk tsunamikompetanse”, Liv Røhnebæk Bjergene, Synnøve Asplund, Bistandsaktuelt (James M. Strout) Sunnmørsposten. 17 January 2005. ”Risikoen mot fjellskred kan reduseres”, Lars Harald Blikra, NGU and Frode Sandersen Approximately 100 press articles and releases in connection with the tsunami distaster in South-Asia 2004, December 2004-January 2005. TV- NRK 1 - Schrødingers katt, 4 January 2005, "Innslag om generering av tsunami", with Carl Harbitz Video, April 2003, "The Storegga slide and the Ormen Lange Gas Field", laget av Ingenium AS for Norsk Hydro (intervju m/Tore J. Kvalstad)

Press and media coverage

Sognsveien 72, P.O. Box 3930 Ullevaal Stadion, N-0806 Oslo, Norway Tel.: +47 22 02 30 00 ● Fax: +47 22 23 04 48

ngi@ngi.no ● www.ngi.no

“When a geotechnical engineer visits NGI, it is like a Catholic visiting the Vatican!”

Homa Lee, USGS,

After the "Submarine mass movements" Conference in Oslo, 7 - 9 Sept 2005

Geophysical methods - Seabed shear wave seismics

Comparison of reflection from pressure and shear waves identifying an overpressured sand body

Seismic modelling exercises are carried out to investigate the differences in reflection from pressure and shear waves in over-pressured sand bodies. These exercises show that over pressured sand bodies in many cases will most probably produce large shear wave reflections, and only small pressure wave reflections. Background and objectives Drilling into a sand body containing high-pressure water, may cause major problems. The “shallow water flows” (SWF) that may arise from this process, will discharge subsurface fluids into the ocean that may damage equipment and delay drilling programs considerably. Methods for localising these over-pressured bodies prior to drilling are therefore of great importance to the offshore industry. Results and findings Seismic modelling exercises have been performed to investigate the differences in reflection from pressure and shear waves in over pressured sand bodies. The results show that over pressured sand bodies in many cases most probably will produce large shear wave reflections, but only small pressure wave reflections. The figure below shows a synthetic seismic shot gather, pressure waves (left) and shear waves (right). The reflection from the over-pressured body is indicated by an arrow. In general one can conclude that shear waves are better suited for mapping of over-pressured sand bodies than pressure waves (P-waves). The interface between an overlying shale and a over pressured sand-body can represent a big contrast for the S- wave, but a low impedance contrast for the P- wave.

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Geophysical methods - Shear wave seismic source. Prototype testing offshore There are several advantages of using seismic shear wave technique for offshore geohazard mapping compared to the traditional methods. This technique can be used in connection with the detection of over-pressured zones, gas hydrates and “weak” layers. Background and objectives The oil industry has been lacking a seabed shear wave source to generate the shear waves needed for seismic shear wave mapping. Statoil, Hydro, and the Research Council of Norway have financed the development and testing of a new prototype seabed shear wave source produced by NGI. The prototype was tested at the Gullfaks field during the summer of 2003. The shear wave source was run in a sweep mode, at frequency of 2-45 Hz, with a dynamic horizontal ground force of 100kN, and in a pulse mode (at one site). Different S-polarization orientations, both radial and transverse were tested. The test was conducted within a 24 hours window during a conventional 4C seabed seismic survey. The OBC (Ocean Bottom Cables) seismic service company has recorded the seismic signals produced by the shear wave source on four 4C ocean bottom cables.

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Results and findings The results show that the shear wave source can generate good quality S-wave data. The electro-hydraulic suction anchor based seabed shear wave source concept was operationally successful. It is a promising technique. A lot of information can be derived from data processing. One may identify a number of shear wave (S-S) reflections, some originating from layers more that 1000 meter below the seabed. The repeatability of the results is excellent for the stiffer seabed sites, from the first shot until the last. Few shots were needed before the shear wave source signature stabilizes at the sites with softer seabeds. The prototype was designed for deep penetration and is therefore quite large and heavy (9 tons) and operates on low frequency. For shallow depth investigation, a lighter and smaller shear wave source version is recommended.

Geophysical methods - Seismic tools for offshore geohazard studies In slope stability studies, important “weak” layers are often thinner than the typical seismic resolution of few metres. Hence, the improvement of resolution and imaging of seismic data and attributes that can highlight various physical properties in the sedimentary rocks is important. The studies performed provide useful guidelines and have strengthened the seismic part of integrated geohazard projects. Background and objectives Seismic reflection data is one of the main sources of information in offshore geohazard investigations. They provide a regional overview of stratigraphy and geological processes and are also the most important tool for correlation between sites of subsurface sampling and measurements. Seismic reflection can be applied through exploration wells, geotechnical boreholes or shallow seabed cores. Seismic resolution, particularly vertical resolution is a major problem in the oil industry. In slope stability studies, the important “weak” layers are often thinner than the typical seismic resolution of a few metres. The objective of the study is twofold; to “streamline” the handling of seismic data for offshore geohazard studies and to investigate the use of various seismic attributes in geohazard studies. Results and findings

Resistivity CPT Probable debris flow deposits

SeisVision and other parts of the Geographix package, such as WellBase and Prizm provide the necessary tools for NGI to carry out geohazard studies on both 2D and 3D seismic data. The most recent programme versions have possibilities to include other data than the traditional wireline logging data. These data are such as index properties measured on core samples, and are included in the seismic sections. A combination of the Geographix software with other programmes, such as Surfer and IRAP-RMS has been tested. Recommendations on how one can treat seismic data in offshore geohazard studies are provided as an aid to future projects. A production line from receiving seismic data through interpretation, inclusion of various down-hole and laboratory measurements in the seismic data, to final production of maps and other representations of results is described. A range of seismic attributes have been studied, mostly on high resolution 2D data from the Storegga Slide area. Amplitude Envelope, Apparent Polarity, Similarity, and Dip or combinations of these are useful attributes to image slip planes both in 2D and in 3D seismic data. Stacking velocities comprise useful information and should be required with the seismic data in geohazard projects. Pre-stack attributes and AVO analyses are necessary to extract information on geotechnical properties. This implies processing expertise and special software, not available at NGI at the present time.

Seismic profile across a geotechnical borehole. The left-hand curve is a resistivity curve (Laterolog) with data gaps, whereas the right-hand curve shows a continuous undrained shear strength profile from CPT data. The theoretical base of the gas hydrate stability zone is indicated with the horizon named BSR. The interpretation of the debris flow deposits is based on the combined data set.

BSR

Geophysical methods - Using electromagnetic (EM) waves for mapping gas hydrates Evidence of gas hydrates are detected by traditional seismic imaging. However, seismic imaging alone cannot estimate the hydrate concentration. The results of the study performed, show that it is possible to detect gas hydrates by means of sea bed logging. Background and objectives Gas hydrates have received an increasing studying interest since the early 1990’s. Gas hydrates are a potential source of energy and hydrate exploitation will require new technologies and techniques. Gas hydrates are also considered a significant hazard in conventional hydrocarbon production terms. They can cause shallow gas release and local seabed instability.

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Evidence of gas hydrates are detected by traditional seismic imaging. However, seismic imaging alone cannot estimate the hydrate concentration and additional measurements like resistivity and/or sonic borehole logs are required. New marine electromagnetic techniques, like seabed logging (SBL), may provide a resistivity map of the formation below the seabed. 21 ohm-m

22 ohm-mThe applicability of SBL to detect gas hydrate layers in the formation was studied. This type of detection could serve as a complement to seismic imaging to estimate the gas hydrate concentration. Results and findings The performed study includes finite element simulations of EM signals through a 1D and 3D layered soil models containing a gas hydrate layer. The simulations show that it is possible to detect gas hydrates by means of SBL, even for low resistivity contrast between the gas hydrates and the surrounding formation.

Detection limit

Examples from the numerical modelling exercise where the EM gas hydrate response is above the

Field monitoring and instrumentation - Subsea instrumentation “Best Practice” A“Best Practice” manual for the design of subsea and offshore instrumentation systems has been defined based on experience from 30 years of instrument design for the offshore industry. The manual contains a summary of relevant measuring techniques as well as recommendations for selection of sensor technology and system solutions. Background and objectives The purpose of this work is to capture the existing practice and experience from 30 years of instrument design for the offshore industry and to make this knowledge easily available for future projects. Ultimately, the availability of this expertise may be employed to improve the efficiency and reliability of subsea instrumentation developed by NGI. Results and findings The result of this project is a 'Best Practice' manual for the design of subsea and offshore instrumentation systems. This manual contains a summary of relevant measuring techniques as well as recommendations for selection of sensor technology and system solutions. Focus is given on a significant number of central issues such as:

• Sensing mechanism and sensor technology • Local attachment and environmental considerations • Power management • Data logging and control systems • Data transfer (communication system) • Cables, connectors, components (hardware considerations) • Physical protection (e.g. trawling and installation loads) • Corrosion, material behavior and selection of materials • Redundancy and alternate measurement technology • Installation methodology

Examples and recommendations for offshore applications are given. The result of this effort is an internal report summarising key technical experience for use by the instrumentation group in planning and executing subsea/offshore instrumentation design projects. A 'Best Practice' manual like this report will be subject to revisions as new technology and experience develops.

Field monitoring and instrumentation - Multilevel piezometer The multi-level piezometer string that was developed during this project provides measurement of pore pressure at several discrete depths within a single boring in soil sediments. The sensor is constructed as a modular construction, allowing variation in the number and location of the monitoring points along the string.The multi-level piezometer provides important mgeotechnical analyses as well as significant cost savborings will be required to obtain the necessary pore pres

aterial parameters for ings, as fewer subsea sure information.

objectivesBackground and

Multilevel piezometer string made up ofheavy armoured hydraulic hose, pressured clamped to piezometer modules. Hose with modules can be coiled on cable spool or handling winch.

(cutaway section to show interior ofmultilevel pieozmeter string)

Each piezometer module connected to internal string network by electricaljumper.

Each piezometer module can measuredifferential pressure and/or total pressure (1 or 2 signal channels)

Up to 8 channels can be connected in the multilevel piezometer string.

Tip fitted with blunt dead weight to maintaintension in string during lowering

Top fitted with lifting cap and electrical connection point.

A piezometer module

A piezometer module. Each module is independent part of string, it can be fieldreplaced if necessary. Failure in module doesnot result in failure in string.

Multilevel piezometer string made up ofheavy armoured hydraulic hose, pressured clamped to piezometer modules. Hose with modules can be coiled on cable spool or handling winch.

(cutaway section to show interior ofmultilevel pieozmeter string)

Each piezometer module connected to internal string network by electricaljumper.

Each piezometer module can measuredifferential pressure and/or total pressure (1 or 2 signal channels)

Up to 8 channels can be connected in the multilevel piezometer string.

Multilevel piezometer string made up ofheavy armoured hydraulic hose, pressured clamped to piezometer modules. Hose with modules can be coiled on cable spool or handling winch.

(cutaway section to show interior ofmultilevel pieozmeter string)

Each piezometer module connected to internal string network by electricaljumper.

Each piezometer module can measuredifferential pressure and/or total pressure (1 or 2 signal channels)

Up to 8 channels can be connected in the multilevel piezometer string.

Tip fitted with blunt dead weight to maintaintension in string during lowering

Top fitted with lifting cap and electrical connection point.

A piezometer module

A piezometer module. Each module is independent part of string, it can be fieldreplaced if necessary. Failure in module doesnot result in failure in string.

of the pore pressure profile is essential in the evaluation of strength and

he objective of the study has been to The determination deformation of sediments. Tdesign a multi-level piezometer string to provide measurement of pore pressure at several discrete depths within a single boring in soil sediments. Before the beginning of this study such pore pressure data were available only via single point piezometer systems in subsea deployments.

esults and findingsR Ti

he sensor is constructed as a modular construction, allowing variation ation of the monitoring points along the string. n the number and loc

The string can be deployed with up to 8 measurement points. Measurement points may include differential pressure, total pressure and temperature. The sensor used is a miniature differential pressure sensor, which is capable of providing both differential pressure as well as total pressure measurements at the module filter. The sensor is designed to be pre-assembled on land, and shipped on cable drums offshore. Installation offshore will be done from a handling winch; the piezometer string is spooled from the winch into the borehole filled with liquid grout. The piezometer string is grouted in place when the grout hardens.

Technical specifications Sensor specifications (as reported by sensor OEM)

Physical characteristics

Differential pressure range: 0.1 to 20 bar (typically 1 to 3 bar ) Maximum line pressure: 200 bar Data signal: RS485 network Sensor accuracy: 0.25% full scale Temperature, oC: -30 to 100 (0 to 50 temp. compensated) Vibration: 20g (20-5000Hz) Power: 8-28 vDC

Diameter: <70mm Material: Stainless steel (other materials can be used) Max deployment depth: 1900m below sea level Submerged weights (estimated) sensor module: 3 kg/module tubing: 1 kg/meter top piece: 2 kg tip piece: project specific (5 - 500 kg)

Sensor module and sensor (visible in the cavity that will be covered by a low air entry filter)

Field monitoring and instrumentation - Monitoring gas charged seabed and hydrates Oil industry requests methods and equipment to enable better knowledge and control when gas is released close to subsea structures and production platforms. Better equipment is needed for monitoring the concentration of dissolved gas leaking out from the seabed as well as in the subsoil. In some cases free gas bobbles can be observed in the field. The amount of bobbles provides important information. Several methods and equipment have been evaluated. Outlines for a subsea gas release measuring instrument have been developed. Background and objectives Gas leakage along casing and conductors as well as pressure charge in shallow layers has been identified as a serious problem in mature production fields. At some mature fields, the gas leakage has lead to critical conditions with shallow layers charged to significant over pressure levels which sometimes results in spontaneous blow-outs from the seabed. This is explained by the creation of leakage paths along casings and conductors in production wells. There is no history of monitoring such leakage mechanisms, and there is limited knowledge about the progress and magnitude of similar problems. However, the consequences may be dramatic, and early corrective actions are necessary to minimize costs and future problems which may affect future production.

The objective for this study has been to identify the uncertainties connected with gas leakage related problems and define relevant technology and required modifications for the described applications. The aim of this work has been to develop a suitable monitoring system to discover gas concentrations and measure gas flux trough the seabed.

Pore pressure sealing unit

Results and findings The following methods were evaluated in the project: SMPD-device

Semipermeable devices (SMPD) are used to measure methane quantities at the sea bottom. The original idea was that these small LPDE plastic films should accumulate methane and give information about the methane flux and identify sea bottom locations for further studies. However, literature studies have showed, that SMPD’s was unable to monitor methane flux.

Sealing mechanism for pore pressure measurements

A low cost method for pore pressure measurements is to install sensors inside existing steel pipes in the sea bottom. A sealing method for such installations has been developed. This method uses a polymer material as sealing material. This polymer expands when in contact with water and seals the space between sensor cable and pipe wall.

Gas flux quantification

Gas trap

Two different devices are developed to quantify the gas flux at the sea bottom. A “gas trap” is designed to be placed over potential pock marks. The amount of gas in this device can be read through the plexiglas windows by an ROV. A gas flux counter has been developed to be able to quantify the amount of gas that is passing through a given area (flux measurement). A series of gas flux counters can be linked together for measurements where the flux is unknown and can vary significantly.

METS sensor

This sensing technology consists of a semi-conductor detector and a diffusion membrane allowing methane molecules to pass. This sensor is available in the market, branded as METS and is manufactured by the German company CAPSUM. Some necessary modifications have been identified through field testing and pilot projects. Application range and stability of the sensor must be improved and this is possible by for example introducing multiple detectors into one instrument. This technology can be also be modified for down-hole use, allowing for continuous in-situ methane monitoring. Hydrates can also be detected as increased methane concentration after melting by introducing a heating element.

fillingTmin

Ventingholes

ValveValve opens and gas is released

Tmax V

Outlines of subsea bobble counter for monitoring leakage of free gas

Field monitoring and instrumentation - Real-time monitoring – Contactless serial interface Different technologies were evaluated for development and implementation of subsea monitoring systems designed for geohazards monitoring at locations without existing infrastructure. Background and objectives The purpose of the work has been to improve technology for the transfer of data from autonomous subsea monitoring systems. Two different aspects of the communication links have been considered - the transfer of data from the monitoring system to a data transmitter via a contactless interface, and the long-distance link used by the data transmitter between the seabed and the end user of the data.

Results and findings Several options are theoretically available in subsea application for short range contactless data communication, such as inductive (magnetic), optic (light pulsing) and acoustic (frequency pulsing).

Inductive signal coupling has proven to be the most attractive and cost effective solution. Related to inductive couplings, is the use of radio signal coupling underwater over very short range. However, this technology has not been identified yet in the commercial market for subsea applications.

Long range data communication is currently being obtained using umbilicals instrument or power-consuming acoustic modems. Low-power transmission via the lifting wire is possible using guided wave technology. However, the wire must be insulated for long range transmission.

Focus will be given on the future following transmission solutions:

• Seabed data collection (ROV handled couplings) - Inductive couplings - Radio transmission coupling

• Long distance data transmission - Signal transmission to surface via ROV’s umbilical - Development of guided wave technology for transmission of data along insulated

steel crane wire

Logging head ( seabed buoy )

Down - hole instruments

ROV

Contactlessinterface

ROV clamp

Logging head

Field monitoring and instrumentation - Miniature subsea logger Background and objectives The miniature subsea logger has been designed by NGI to be a flexible interface for deploying a variety of sensors or instruments. Focus has been given of the physical dimensions of the logger, to allow it to be installed together with sensors (e.g. the multilevel piezometer) via a standard drill string used for geotechnical investigations. The logger is fully programmable by using the C language, allowing great flexibility in data processing onboard, reduction and data conditioning. The programmable interface allows the logger to be connected to existing monitoring networks. It can also be programmed to communicate in the protocol of the network. The logger has up to 2GB internal memory, and is scalable to up to 128 measurement channels. Serial and analogue sensor inputs are supported, as well as serial/USB communication. Most of the standard sensors may be deployed with the micrologger. Results and findings The logger is designed as a module which can be added to a sensor bundle. The programmable interface unit offers the following services: • Scheduling of data collection from sensors • Temporary internal logging of data (backup data storage) • Power switching (between several power sources) • Analogue/Digital conversion • Packaging and transmitting of data in system protocol (programmed)

The assembled interface unit. The unit is photographed without any fixation elements attached (i.e. cable fork termination or adapter for the hydraulic line of the multilevel piezometer).

Cable fork termination used by NGI and the end cap of the interface unit. The cable fork, or any other fixation device, can be attached directly to end caps of the pressure container using screws. The end caps are held in place by shear bolts above the O-ring seals. (See also photos above and below).

The Persistor logging card is incorporated in an NGI circuit card. Mounted to end cap of micrologger pressure container (prototype development stage)

Technical specifications Interface module physical Electrical/functional

Diameter: 70 mm Length: 315 mm Weight: app. 5 kg dry, 3.5 kg wet Material: Stainless steel Max. depth: (est. 2000 m, subject to pressure certification)

Signal in from sensors: Serial or analogue Communication: Serial (RS232 or RS485 can be provided) Power supply: 12vDC nominal, 3.6 to 20vDC internal power is 3.3vDC) Sensor channels: up to128 (see note) A/D conversion: selectable 12 or 16 bit, up to 8 channels Programming: Fully programmable using C Power consumption: ~20 μA sleep, 2mA to 60mA active*

*power consumption is only approximate, and will depend on activity level in logger. Sensor power consumption is not considered.

Soil investigation methods - Geotechnical optimisation and design criteria of seabed sampler

Testing of sampler at Onsøy, Norway

Detailed design criteria for a new sea bed sampler have been established to improve the sampling technique for up to 25 m long high quality samples in water depths of up to 2000 m. A prototype sampler has been built and tested onshore and offshore. Through field and laboratory testing it is found that the new sampler gives high quality samples. However, more work is needed regarding offshore handling of the sampler. Background and objectives There is a well documented need for developing a seabed sampler that can take up to 25 m long samples of high quality in water depths of 2000 m. The objective of this work has been to give detailed design criteria for a new long seabed sampler, and to assess the quality of samples obtained with a prototype both onshore and offshore. The aim has been to improve sample quality and the new samplers should be at least as good as the ones obtained from a thin walled piston tube sampler in the bottom of a borehole. Results and findings The design criteria of the new sampler were selected based on a detailed literature study, special laboratory tests and finite element studies. The Dutch equipment manufacturer, AP van den Berg identified material to be used for various parts of the sampler. They also made detailed design of the sampler including innovative solutions for the core retainer, piston and cutting shoe. Further on, AP van den Berg, manufactured a prototype sampler that was tested on onshore NGI’s soft clay research site at Onsøy, outside Fredrikstad in Norway in April 2005. The sampler was finally tested in connection with a soil investigation carried out by Statoil at the Troll field at 305 m water depth. The British soil investigation contractor Lankelma was an active partner on the onshore and offshore field work. Results of laboratory tests carried out by NGI have been compared with previous tests on high quality samples. The conclusion from the comparative testing is that the new sampler can give high quality samples at least as good as the ones obtained from a thin walled piston tube sampler in the bottom of a borehole. Thus the main project objective has been fulfilled. However, more work need to be done regarding the handling of the sampler offshore.

Soil investigation methods - Characterisation of soft soils in deep water by in situ tests An improved quantitative framework to characterise soft offshore shallow sediments associated with deep water investigations by situ testing methods; CPTU, Vane and T-bar with most emphasis on the T-bar has been developed. Background and objectives The objective of the study has been to provide an improved quantitative framework to characterise soft offshore shallow sediments associated with deep water investigations by situ testing methods; CPTU, Vane and T-bar with most emphasis on the T-bar.

Results and findings Comprehensive and laboratory field tests carried out at NGI’s soft clay site in Onsøy and by COFS in Perth, Australia. The results show that the CPTU cone and T-bar penetration resistances and vane torque resistance correlate best to the average shear strength determined from compression and extension triaxial and direct simple shear tests. Finite element analyses of T-bar penetration based on the Onsøy and Burswood laboratory test data, shows that the theoretical NT-bar -value for a T-bar in undisturbed clay may give reasonable values of the average peak undrained shear strength. This appears mainly due to compensating effects from (a) strain rate (tending to increase penetration resistance) and strain softening (tending to decrease penetration resistance). The effect of these compensating factors may depend on the clay type. The intensity of these compensating effects differs for other clays with different rate effects, anisotropy ratio, strain softening and sensitivity. The figure below shows results from finite element analyses of a case with anisotropic shear strength and strain softening in Onsøy Clay. Very distinct shear zones development can be observed.

a) Load displacement of T-bar b) Shear strain development below T-bar

Laboratory methods - Correction methods for oedometer testing The conventional procedure applied when soil samples are extracted from the site to the laboratory and later prepared for testing, will lead to disturbed samples compared to the in situ state. A procedure for adjusting the constrained oedometer modulus extracted from disturbed soil samples has been proposed. An accurate determination of the pre-consolidation stresses was found to have significant imortance for the proposed correction method. Background and objectives The procedure applied when soil samples are brought from the site to the laboratory and later are built in the requested apparatus for testing will lead to samples being disturbed compared to the in situ sample state. Oedometer test data from soft clay samples have been studied in order to establish a procedure for adjusting the constrained oedometer modulus extracted from disturbed soil samples. Results and findings An accurate determination of the pre-consolidation stress was found decisive for the proposed correction method, and four different methods for pre-consolidation determination were analysed and compared: Becker, Casagrande and Janbu together with a new method. The curvature of the axial strain – axial stress data (linear scale) was evaluated. Some of the project findings can be summarised below:

• The new method for determining the pre-consolidation stress leads generally to results comparable with the pre-consolidation stress found by Casagrande and Becker except for lean clays where the new method leads to approximately 10 % higher yield stresses.

• Increasing the number of methods in the determination of the pre-consolidation stress, implies that the uncertainty of pre-consolidation stress may be reduced; this is especially valid for disturbed samples where previously published results seems to be low compared to block samples and to results obtained by combining the investigated methods.

• The pre-consolidation stress of a disturbed sample will be lower than for an undisturbed sample. • The pre-consolidation stress results from the methods applied, have been calibrated by using the exact location of

the pre-consolidation stress in the Janbu modulus plot. No distinct results have been found. • The constrained oedometer modulus measured on disturbed samples for stress levels lower than the yield stress,

will be lower compared to undisturbed samples. Modulus values for stress levels between the yield stress and 2-3 times the yield stress will generally be higher on a disturbed sample compared to undisturbed sample.

• The stiffness of the soil sample for stress levels lower than the yield stress is uncertain. It is likely that the initial stiffness is determined too low; even for high quality samples. Suggestions for updating CRSC-laboratory procedures, both considering the stiffness but also considering other laboratory-specific aspects have been given.

• Adjusting the modulus value on a high quality samples gave similar results compared to the unadjusted modulus value (a very small correction if the sample is undisturbed). Samples from exactly same location represented by high and low sample disturbance, were used to verify that the proposed method lead to realistic modulus values even when used on disturbed samples.

• Suggestions have been given for additional work.

10 100 1000σa' [kPa]

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Interpreted pre-consolidation stressindicated by an arrow

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p'0

Interpreted pre-consolidation stressindicated by an arrow

Left: Stress strain relationship from CRSC testing on disturbed and undisturbed material. Right: Tangent modulus values versus axial stress.

All the features addressed above have been implemented in a user-friendly software package. It presents results by a graphical interface adopting measured data in an electronic format from the la-boratory. The sample disturbance effect is visualised on the figures below considering oedometer testing (constant rate of strain).

Remoulded shear strength measured measured by different tests in Onsøy clay

sur lab vs. APvdBerg Sleeve friction

y = x

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engt

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UU tests

Fall cone

Field vane

Laboratory methods - Measurement of remoulded undrained shear strength The remoulded shear strength of soils/clays is an important parameter in offshore slope stability analyses. There are several methods to measure and determine the remoulded shear strength. Consequently, there can be significant differences in the strength values used for design. A database containing remoulded shear strength data has been established. Background and objectives The remoulded shear strength is an important parameter for the design of suction anchors for example as well as offshore slope stability analyses. In slope stability analyses, the remoulded shear strength influences the failure mechanism and the progressiveness of a potential slide. Experience has shown that the remoulded shear strength depends on a large extent on the measuring method used either in the laboratory or in the field. There is currently no consistent, universally recognized measuring method and thus there is an obvious necessity to develop measuring guidelines. Results and findings A literature review concludes that there are many types of laboratory tests (e.g., fall cone, lab vane, UUC test, torvane, pocket penetrometer, ring shear) and in situ equipment (e.g., field vane, CPTU, T-bar) to measure the remoulded shear strength. Some of these methods are essentially a direct measure of the remoulded strength while others are indirect and rely on theoretical and/or empirical correlations. The methods used to remould soil also vary. There are found different correlations to determine the shear strength. Consequently, there can be significant differences in the strength values used for design. A database containing data from a number of consulting and research projects involving clays of varying plasticity and mineralogy has been established at NGI. Analysis of the database has confirmed the conclusions from the literature review. A Joint Industry Project (JIP) will be proposed based on the results in this project. The work scope of this JIP will be: 1) Further develop and study of the NGI-database of remoulded shear strength; 2) investigate rate effects, ring shear testing and influence of mixing/remoulding procedures; 3) conduct laboratory tests for a selected number of soils; 4) develop recommendations on equipment and test procedures for measurement of remoulded shear strength.

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BothkennarLierstrandaAriakeBangkokVarious clays

Range expected for"perfect" samples

Laboratory methods - Suction in clay samples This study shows that the use of suction measurements used in conjunction with other soil parameters gives an indication of sample quality. Background and objectives The main objective of this study was to develop a scheme for using reliable suction measurements to explain anomalies in measured shear strength values from index tests. This would allow evaluation of sample disturbance for selection of best quality specimen for advanced testing. The possibility to use suction values to correct laboratory results on samples that have been reconsolidated to in situ stresses have been studied. The evaluation of Ko, in respect with the use suction values, especially in heavily over consolidated clays has also been studied. A comprehensive literature review and laboratory measurements of suction on two soft clays; Norwegian Onsøy clay and Irish Ballinasloe clay was conducted. Results and findings The literature review reveal that there is a clear relationship between measured suction value and sample quality and that anomalies in index shear strength may be explained by loss of suction due to stress relief. However, a considerable amount of uncertainties are associated with this argument. Measured suction depends on the details of the measuring technique; the procedure used to seal, transport, store and prepare the samples, the elapsed time between testing and sampling as well as the effect of the field sampling technique and the soil type itself. Five different techniques of suction measurements were performed on samples of varying quality from two test soils in the laboratory. The sample quality indicated by suction measurements was the same as compared to triaxial (CAUC) stress/strain curves and stress paths. A clear relationship between measured suction and the well known sample quality indicator Δe/e0 was found. Suction values derived from the cell pressure loading, filter paper and tensiometer techniques seem very similar, with the latter technique showing the lowest values in most cases. All of above mentioned techniques were found to give values slightly less than those recorded from the University of Massachusetts suction probe. The final method used - the Japanese approach - gives very low suction values. In the absence of a standard well proven method, it is recommended that two of the three techniques; cell pressure loading, filter paper and tensiometer techniques are used to obtain an average value. However it must be emphasized that other researchers have stated that these measurements can be misleading when used separately. These results should only be used in conjunction with other soil parameters measured in the lab, e.g. Gmax.

Databases - Correlations between index and soil design parameters A database for the Caspian Sea soils to allow for correlation studies between index test data and laboratory measured soil design parameters was established. These parameters required for foundation analyses and geohazards studies. The results of the correlations studied, show a large degree of scatter. However, the in situ conditions of combined high pore fluid salinity and excess pore pressures, make the Caspian Sea sites unique. Background and objectives The objective was to develop and analyse a database of high quality geotechnical data for the Caspian Sea sites ACG (Azeri, Chirag and Gunashli) and Shah Deniz PSAs. The database allows for the study of possible correlations between index test data and laboratory measured soil design parameters which required for foundation analyses and geohazards studies. Various methods for performing the liquid limit test were studied. The possibility for correlations development for converting results from one method to another was also studied. Results and findings Data on liquid limit measurements both from the literature and measured at NGI were analysed to develop correlations between the different measurement methods. Good correlations were found and recommendations are given in the report for converting Vasilev (Russian) or Casagrande Cup liquid limit measurements to the equivalent Fall Cone (European) value. In general, most of the considered correlations show a large degree of scatter even for basic index relationships. Several factors contribute to this scatter including sample quality, fissured and slickensided sample, laboratory stress state, high pore fluid salinity and excess in situ pore pressure. Somewhat, reasonable correlations were

found for stress sensitivity vs. void ratio sensitivity, remoulded undrained shear strength vs. liquidity index, and undrained shear strength vs. preconsolidation stress. Consolidation-flow correlations showed high scatter with almost no trends.

The analysis presented suggests that the Caspian Sea soils, while often fissured and slickensided, are not necessarily unique relative to other soils worldwide. It is rather the in situ conditions of combined high pore fluid salinity and excess pore pressures (Δu) that make the Caspian Sea sites unique. Determination of Δu is the major challenge, as it is difficult and time consuming to measure. Significant uncertainties still exist on the magnitude of Δu is at the various ACG sites.

Relationship between liquid limit as measured by Russian Standard and ASTM

Databases - Offshore geotechnical borings Background and objectives Develop a database containing offshore geotechnical borings. The database should be integrated in a general GIS-tool and should have the possibility to register new geotechnical borings as well as perform search in existing data. Example of map used a start position to localise borings. Offshore installations indicated with yellow signs. Results and findings An Access database has been designed with user interface to register new offshore geotechnical borings and to search in existing data. All offshore geotechnical borings since 1971 are included. These borings are linked to a NGI-project and labelled uniquely within that project. Corresponding reports are also linked to the database. These borings are classified by unique geographical position, type and key geotechnical data. Geotechnical borings registered in the Gullfaks/Statfjord area.

Databases - Geotechnical data Background and objectives The objective of a database containing geotechnical data is to ensure an effective and safe dataflow starting when samples are collected offshore, via laboratory testing and ending on data reporting. Results and findings A geotechnical prototype database for effective dataflow and safe storage of offshore geotechnical data has been designed. This database will be a tool for effective reporting and data storage, and it will be useful for regional studies. Research activities will also benefit from this database due to increased opportunities for effective production as for instance correlations between various geotechnical and geological parameters. The database will include information about:

• Projects • Sites/wells/borings • Geotechnical key test parameters • Links to test data plots • Index parameters • Geological data (mineralogy from XRD, carbonate content, etc)

Example of data correlation. Database prototype design

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Databases - Information system for geotechnical laboratory data Background and objectives Define information system (IS) for geotechnical laboratory data. The IS shall be the main system for registration, administration, specification and presentation of laboratory data at NGI. This system shall rationalise and standardise work processes in the laboratory, and improve data retrieval, for clients and partners in a functional way. All elements in the dataflow from the moment a sample is collected in the field, through test specification, testing and finally result presentation have been mapped before specifying the system.

loggingautomatization

processing

test ID spesification result report history

loggingautomatization

processing

test ID spesification result report history

Description of data flow Results and findings The laboratory IS system must have the ability to:

• specify/order laboratory tests via intranet or internet • register laboratory data • retrieve data

– reproduce plots – plot correlations – group test results on optional criteria

• administrate test stockroom – register test in/out of stock – bar code system/LIMS – test description

Performance specifications from all relevant user groups at NGI were obtained through interviews and workshop. Specification for the IS system have been established.

Databases - Improved field monitoring Background and objectives Improve techniques to monitor and detect geohazards. Results and findings Field monitoring stations that automatically transfer data to databases have been established. The content in the databases are checked and transferred to end-users and clients using GIS- and WEB-solutions. Battery-driven data loggers (Rio or Campbell) for collecting field measurements are included. The loggers transfer data from sea bed via ROV or umbilical to the communication centre by using satellite technology or GSM connection to onshore station. The transfer of field data takes place automatically in given intervals. Data are displayed in an extranet WEB-solution which is protected by password. This solution gives possibility for quality control of data, calibration adjustments; check of hardware and errors as well as publishing data to external users. A simplified solution for showing the different sensors with geographical position is included. The user can move rapidly to the desired position. The digital map shows the sensor within an area and indicates if a sensor is in operation or not. External users may view and approve published data. Collected data for each sensor are shown together with alarm for a specified time interval. Comparisons with other relevant data are possible.

Databases - Slides and offshore geohazards Background and objectives Studies on avalanches and slides require a register (database) for documentation. Important information is when and where the slide occurred. However, scientists need more information for further studies such as type of slide, size, damage caused and release mechanisms. Today there is no such centralized database for slide events in Norway. Slide events are registered locally unsystematically from different persons and institutions. The aim of the project has been to develop a database for all types of slides. The project is coordinated together with NGU which administrates the web site www.skrednett.no. To provide a tool for collecting and summarising sediment information that it is relevant for offshore geohazard evaluations, research at ICG and within the EUROMARGINS project, as well as other NGI projects. The objective has been to have a database that can be linked to other databases at NGI. Results and findings A slide database containing meta-data such as; who has registered a slide, who has observed the slide, and the accuracy of the registration has been established. Classification criteria for all type of slides, from submarine to large rock falls have been developed. The different snow types are defined in an international snow classification chart. Several thousand avalanche registrations exist in Norway today. All of this data will be collected and administrated in a secure and systematic database during the next year. The finalised database will be available for the user through the internet. In this way, anyone can register a slide observed in the nature. The registered slides will be visible on a map, thus allowing the slide activity during the past week for example to be visualised. In combination with hazard zoning maps, this slide database will give valuable information for different users such as road/rail road authorities, communities as well as for anyone that may need this type of information.

Geometry of a snow avalanche. Graphical illustrations like this will be included in the registration of the database to allow the user to input data easily.

The offshore geohazard database was constructed by using Microsoft Access. Data from the mid-Norwegian margin has been entered in the database.

Physical processes - Gas migration mechanisms Shallow gas may influence the stability of the sediments and cause difficulties in drilling operations. Basic mechanisms for gas flow and migration in shallow sediments have been identified and possible methods to simulate gas flow and migration have been investigated. Background and objectives Shallow gas related to offshore geohazards is most often located in the upper 500 m below the seabed. The gas may influence the stability of the sediments. Thus locating the gas is important for planning and execution of several offshore activities. Shallow gas may cause difficulties particularly during drilling operations because it can be encounteredin the drilling locations without casing and blow-out preventer. Drilling into an over-pressured zone may result in unstable wellbore and blow-outs. The primary objective of this study has been to identify the basic mechanisms for gas flow and migration in shallow sediments and investigate possible methods to simulate gas migration and flow.

Gas leakage from a pressurized and permeable sand layer in i i it f ff h i t ll ti

Results and findings

Simulation of water displacing gas.

A literature review related to shallow gas migration, modelling techniques and detection methods has been conducted. The condition of the gas in sediments depends primarily on formation temperature, pore pressure and gas saturation. The resulting state of gas is either free gas, dissolved gas or gas hydrates. Gassy sediments often contain a combination of all three states. Mechanisms for gas transport can be divided into four different categories; Dispersion and diffusion of dissolved gas, Darcian two-phase flow, Dilatancy controlled gas flow, Gas transport in tensile fractures. Darcian two-phase gas flow has been modelled by finite element simulations using Comsol Multiphysics (Femlab). The result of a simulation at a particular time step is shown on the right. The figure illustrates a region with high gas saturation (yellow–green) surrounded by formation saturated with water (red). The gas is being pushed through the permeable layer in the centre, as water is flowing from the left to the right boundary. The green arrows indicate the flow velocity.

Model of sedimentation process. Red colour symbolise layers already sedimented Yellow colour in layers currently under sedimentation and blue colour in layers to be sedimented.

Physical processes - Pore pressure during sedimentation

Reliable prediction of the pore pressure distribution in the sediments is essential when evaluating slide hazard. Pore pressure build-up depends on the sedimentation process.

Background and objectives A key factor in evaluating the slide hazard is the ability to make reliable predictions of the pore pressure distribution in the sediments. The pore pressure is a function of the sea bottom topography, layering of the sediments, rate of sedimentation, thickness of the sediments, and previous landslide history, among others. The aim of this study has been to perform one- and two-dimensional subsea sedimentation to study effects on pore pressure build up of horizontal water flow caused by an inclined seabed. Results and findings A one-dimensional numerical tool, Basin-1D, has been developed to make such predictions. To better account for layering, sea-bottom topography and two-dimensional pore-pressure dissipation, to expand Basin-1D to two dimensions, that is called Basin-2D. The differential equations have been established, the finite element model for a single element was formulated and issues related to treatment of boundary conditions and modelling the process of sedimentation have been addressed. The commercially available finite element code PLAXIS was used to perform the two-dimensional analysis. It was found that PLAXIS has all features necessary to carry out one and two dimensional sedimentation analyses, but some user experience with PLAXIS that consolidation analyses is advantageous to avoid numerical problems during analyses. Model comparisons between PLAXIS and Basin-1D were performed, and a user’s guide to run sedimentation analyses in PLAXIS was established.

Physical processes - Material instability and development of slides

A progressive failure mechanism in natural slopes with soft, sensitive clays with strain-softening behaviour has been successfully modelled and found to promote long-scale failures.

Background and objectives Slope stability is conventionally investigated by using some form of limiting-equilibrium method, assuming perfectly-plastic material behaviour. However, many soil materials (such as sensitive soft clay) may display strain-softening (i.e. a decrease of shear strength with further deformation after a peak strength has been reached). Strain-softening is known to have a negative effect on stability due to the progressive failure development. The objective of this study has been to investigate progressive failure in slide mechanism for a long natural slope. Results and findings A soil model (ANISOFT) that takes into account anisotropy and strain-softening is implemented as a "user defined" model in the finite element program PLAXIS 8.1. The model has been used to study the effects of progressive failure for a wide range of cases.

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Simulation of progressive failure in a long natural slope Progressive failure affects both the necessary load to initiate a slide and the failure mechanism. Progressive failure has a negative effect on stability by reducing the necessary load for initiation of the failure compared to that of a perfectly plastic material with the same peak strength. Furthermore, it is found that progressive failure may promote large scale failures.

Figure 1 Stress - strain relationships in shear bands

Figure 2 Critical failure mechanism for perfectly-plastic and strain-softening clay slope.

Physical processes - Progressive failure in soft clay

Soft sensitive clays may fail progressively. Shear bands with strain concentration develops during such failure. An interface element has been developed to model this behaviour and successfully implemented in PLAXIS.

Background and objectives Shear bands with strain concentration develops during progressive failures. To be able to model the phenomenon numerically with the finite element method, an interface element may be used to capture shear strain localisation. A critical input parameter to the numerical analyses using the interface element is the shear band thickness. Using directly the shear stress-shear strain curve obtained from laboratory tests as input, the capacity (peak load) is decreasing with decreasing shear band thickness. For a shear band thickness of some few millimetres, the capacity can be as low as the capacity corresponding to the residual strength. Results and findings A finite thickness interface element for modelling shear strain localisation has been developed and successfully implemented in PLAXIS (see Figure 1). The use of this element has been demonstrated by an example of a downward progressive failure in a slope. The failure was initiated by the construction of a fill near the crest of the slope as illustrated in Figure 2.

In order to estimate the shear band thickness, a hypothesis where the shear band thickness is governed by the loading rate is studied. The time dependent mechanisms are local pore water flow (dissipation from the shear band) and time induced shear deformation (visco-plastic strain or creep). The input to the numerical analyses is obtained from undrained shear tests with varying shear strain rates (see Figure 3). The local pore pressure dissipation is governed by the constrained unloading modulus and the permeability. The main conclusion from this study is that a unique rate dependent shear band thickness is obtained in the first part of the strain softening branch (see Figure 4). For typical deformation rates, the shear strain localisation with development of a very thin shear bands at the peak strength is prevented this is achieved by pore pressure dissipation to the neighbouring zones and increased shear strength with increasing strain rate (see Figure 3).

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Example calculations without visco-plastic strain

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Physical processes - Earthquake response analysis

The computational model NonSSI (Non-linear Soil-Structure Interaction) was developed to improve the seismic analysis of structures.

Background and objectives The soil-structure interaction (SSI) analysis of large structures, is often performed using spring-dashpot elements to represent the stiffness and damping properties of the soil-foundation system (Figure 1). In most cases, only the horizontal foundation spring is non-linear; it is therefore, an important issue for these models the possibility of defining realistic force-displacement relationships for the foundation spring. The objective of this research has been to develop a general computational model for the seismic analysis of the SSI system shown in Figure 1 using different nonlinear force-displacement relationships for the horizontal spring.

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Fig. 1 – Key features of computational model NonSSI Fig. 2 – Nonlinear force-displacement in horizontal spring

Results and findings The computational model NonSSI (Non-linear Soil-Structure Interaction) was developed. The structure in this model consists of beam elements with concentrated masses. While the vertical and rocking springs are considered linear, the horizontal spring is represented by a multi-surface kinematic hardening model. Figure 2 shows the hysteristic response of this spring during a loading/unloading cycle. In addition, a simple strain-softening spring model has been implemented in NonSSI. Plots of an example response for this spring is shown in Figure 3. Another spring model which is under implementation is the model shown in Figure 4 which represents the dilatant response of saturated sand under large displacements. One of the key aspects of this model is its small hysteristic damping in cyclic response.

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Fig. 3 Force-displacement in strain-softening spring Fig. 4 Dilatant spring model

Fig. 1 Typical shear stress – shear strain loops for loose to medium dense sand

Physical processes - Material model for earthquake loading Background and objectives In soil-structure interaction (SSI) analysis of heavy structures on loose to medium dense sand or silt, it is important to have a material model that describes the key features of the soil under cyclic loading. These features are; 1) Pore pressure development with increasing number of cycles and a corresponding reduction in the cyclic stiffness, 2) A “banana” shaped shear stress – shear strain hysteresis loop under large pore pressure build-up, where the tangential stiffness is lowest at low shear stresses (Figure 1).

Results and findings A material model based on the framework of hypoplasticity was evaluated. The stiffness is governed by the present void ratio compared to the stress dependent maximum and minimum void ratios (i.e. current relative density) and the current stress state (i.e. mean effective stress and maximum shear stress). The phase shift from contractant to dilatant behaviour is controlled by the void ratio at the critical state (i.e. the state where the tangential shear stiffness is zero). The model also describes the different behaviours during loading and unloading, with contractance during unloading after dilatant behaviour during loading (Figure 2). This characteristic behaviour is not described properly by models based on elasto-plasticity, where the initial unloading branch is elastic. The main short-coming of the model is the reloading phase. The model does not contain any information about the stress history and therefore the behaviour during reloading is as for virgin loading at this state. This short-coming has been improved by including inter-granular strains that describes the deformations at the interfaces between the grains.

Fig. 2 Effective stress path for strain controlled un- drained cyclic DSS test calculated by a standard

Fig. 3 Shear stress–shear strain loops for strain controlled undrained cyclic DSS test calculated by a standard

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Numerical methods - Tsunami analysis Submarine slides may generate tsunamis. Tsunamis generated from submarine mass movements are often modelled with fixed shape slide block as a source. However, submarine slides like the Storegga slide, develop during a continuous retrogressive process. A computer program capable of calculating tsunami surface elevations caused by a variety of submarine slide sources, i.e. fixed shaped slides, deformable slides and retrogressive slides has been developed. Background and objectives Develop a computer program capable of calculating tsunami surface elevations caused by a variety of submarine slide sources, i.e. fixed shaped slides, deformable slides and retrogressive slides. Tsunamis have previously been modelled with the assumption of fixed shape slide block as a source. Today, it is believed that some submarine slides like Storegga, develop during a continuous retrogressive process involving strain softening soils. An important issue is therefore the ability to model and analyse the initiation and propagation of tsunamis that are related to retrogressive slide sources. Results and findings The work is based on an analytical model developed by Steven Ward, and implemented to predict tsunami surface elevations on simple 2D bathymetries. This model has been used to analyse effects on the tsunami from different slide characteristics such as length, frontal area, acceleration and velocity. The results have been compared with a numerical 3D model. The results from the 2D analytical model confirm the results from other models using fixed shaped slide blocks. The 2D analytical model show that dispersion effects on surface elevation are small for typical slide velocities of submarine slides (see figure). It is shown how the slide acceleration controls the build-up of the wave, and that the slide length governs the total time the wave build-up will last. Modelling the tsunami source from retrogressive slides has been started, and the first results show that the many similarities with models using fixed shaped slide sources.

Effect of dispersion on surface elevation

Overview of the CFX-4 input and output file hierarchy. Red lines indicate the components from CFX4 which are primarily used by NGI. The blue lines show the external post-processing components

Numerical methods - Slide dynamics. Modelling tools

Numerical simulation of submarine mass flow is essential when evaluating slide consequences. The computational fluid dynamics code CFX has been tailor-made to model submarine slides in strain softening material and is set up to model turbidity currents. Other computer codes have been tested to model slide dynamics with different types of material. Background and objectives Using the computational dynamics code CFX4 as an enhanced tool for numerical simulation on mass flows, it strengthens “best practise” method in geohazards slide risk assessment studies. For submarine slide applications it is important to gain an in-depth understanding of the different phases during the development and break-up mechanism of slides and their interaction with the ambient fluid. Another important motivation for the work is to increase the NGI expertise in modelling slides of various types offshore as well as onshore. Another idea is to discover and explore similarities between various slide types and different approaches. Existing slide models/tools have been evaluated and the NIS rheology has been improved with respect to handle more granular types of flow. Results and findings User-defines FORTRAN routines for different kind of mass flows for CFX4 have been developed and applied. Post-processing methods for the evaluations of consequences of slides/mass flows have been developed. The post-processing tools are based on OpenDX, i.e., analysis of the results, by means of visualization using graphs, contour lines etc. In transient problems, animations are used as an important tool to get a better understanding of flow problems. Models for submarine slides (mudslide for clay-rich soils with strain softening rheology, turbidity-current with two erosion models to chose) have been applied. Snowdrift with the possibility of external forcing and nesting with meso-scale weather model and calculations have also been implemented. The strain softening visco-plastic flow model reproduces impressively well a

retrogressive sliding mechanism. The figures below give an example of the computational fluid dynamic analyses. The flow shows the formation of shear bands with concentrated strain softening along the base and behind the frontal toe wedges of nearly intact material. At the initial stage, the modeled behavior is in close agreement with the finite element analyses of a slope with a strain softening layer. The dynamic wedge model is adapted for explanation of the Storegga slide as an example as a retrogressive slide process. Theoretical work on rheology for different granular type of slides has been done. CFX has been tested by calculating impact forces on pipes.

Computational fluid dynamic analyses of a submarine slide in strain softening clay: Shear strength, sensitivity, and velocity

Titan2D, a model developed by the University of Buffalo is based on Savage-Hutter rheology, was tested in case study on the Åkneset slide (Norway) (see figure below). Similar tests are performed with the particle flow code, PFC3D. The figure below shows test runs for a simple topography.

Simulation with Titan2D from GMFG, University of Buffalo, for a case at Åkneset. Shown is the velocity 35 s after release (left). Snapshot from PFC3D simulation for a simplified geometry (right)

Numerical methods - Erosion mechanisms

Background and objectives Identification of possible mass erosion mechanisms in gravity-driven flows. Results and findings The proposed erosion mechanisms are classified according to their spatial position within the slide and the flow regimes in which they occur. As an example, for a class of gravity-driven flows, with relevance to natural geohazards, snow avalanches are chosen and it clearly shows the importance of erosion for the flow dynamics. It also demonstrates the relevance of the material properties at the interface between the slide and slip surface. The former example is considered since it is possible to compare the proposed mechanisms with field measurements and observations. Process-specific models are proposed for erosion by impacts, abrasion, plowing, and blasting. Comparison between model prediction and observations has shown good agreement.

Erosion mechanisms – snow avalanche. Wood engraving by H. Scheufelelein in the Theuerdank 1517

Impact erosion

Numerical methods - Slushflow model

Background and objectives Slushflows - flowing mixtures of snow and water - constitute a natural hazard especially in higher latitudes, i.e., Norway, Iceland, or Alaska. The combination of high density and mobility of the slushflows, can transform them to be highly destructive. Results and findings A slushflow model that considers the slushflow and the ambient air as a two-phase flow is presented. Air is assumed as a continuous gas-phase and slush is assumed as a dispersed multi-component “fluid” consisting of snow clods and water. The rheological model of a non-Newtonian fluid is used to describe the behaviour of the slush and includes visco-plastic and granular effects. The yield strength is assumed to depend on the snow density and the water content. The viscosity of the water and air component is estimated by using the Krieger and Doughert expression for a suspension of snow in water and snow in air, respectively. For the turbulent closure the Smagorinsky LES model is used.

As a case study, the model is run for the slushflow event in Patreksfjörđur, Iceland, on 22 January, 1983. Comparison between field observations and numerical modelling are in reasonable good agreement.

Simulated maximum dynamic pressure; slushflow simulation with CFX4. Left panel, disregarding the interaction with the snowpack and, right panel, including interaction

Analysis methods - Visualisation of slides

Slide visualization technique is a powerful tool, which helps to gain in-depth understanding of the problem and to give elaborated answers to questions. Slide visualization techniques help to simplify numerical analysis and improve the interpretation.

Background and objectives Presentation of slide visualisation possibilities in order to present results from slide models to a client, facilitate the pre-processing needed to initialise numerical models and assist in the developing phase of numerical models. Results and findings The NIS model - a numerical code used in slide risk assessment – was further developed and coupling it with slide visualisation techniques was investigated.

Combined presentation of data bank information with model results and final mitigation measures.

Presentation of model results

Analysis methods - GIS applications Background and objectives Take advantage of bathymetry data to: • visualise results from

offshore site investigations

• optimise the interface between terrain model and calculation programs

Integrate presentation of geotechnical data with other site specific data (geological, geophysical, etc) Results and findings It is recommended to use special modules for visualisation of 3D data integrated with GIS-systems. • Data from site investigations should be stored

in database to simplify presentation and visualisation

• Seabed maps/bathymetric maps can easily be used to show localisation of borings/soundings and subsea installations

• Parameter variation may of water content for example, shear strength etc, may be illustrated by using colour intensity scales

• Snapshots of 3D models with points or bars as shown in the figure below may be used

• Snapshots of 3D models with interpreted soil layering may be used • Sections from 3D models with interpolated values are possible

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Analysis methods - Risk management The objective was to develop a unified and user-friendly framework and use it in practice to illustrate its application for different problems. A detailed study was prepared for the analysis of an underwater slope. To simplify communications, a glossary of terms, today accepted worldwide, was developed. Background

Figure 1 NORSOK Z-013 standard (2001)

Risk management is an integrated and iterative process, including danger identification, hazard assessment, consequence/elements at risk identification, vulnerability assessment, risk quantification/estimation, risk evaluation and risk management. There are two types of approach in risk assessment, a qualitative and a quantitative approach. In qualita-tive risk assessment, the components of risk are expressed verbally and the final result is in terms of ranked or verbal risk levels. Quantitative risk assessment involves quantification of landslide risk components and computation of risk from these components. The quantitative risk assessment frameworks proposed in the literature have the common objective of answering the following questions:

1 What are the probable dangers/problems? [Danger Identification]

2 What would be the magnitude of dangers/ problems? [Hazard Analysis]

3 What are the consequences and/or elements at risk? [Consequence/Elements at Risk Identifica-tion]

4 What might be the degree of damage in elements at risk? [Vulnerability Analysis]

5 What is the probability of damage? [Risk Quantification/Estimation]

6 What is the significance of estimated risk? [Risk Evaluation] 7 What should be done? [Risk Management]

In the Norwegian petroleum sector, the NORSOK Z-013 standard considers safety management and risk control (Fig. 1). This NORSOK standard presents requirements for the planning, execution and use of risk analysis.

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Results The following results were achieved:

• A glossary of risk assessment terms was completed, and adopted worldwide • Two state-of-the-art papers on risk assessment and management was prepared and presented

internationally (includes underwater slope instability). • A framework for integrated risk assessment in practice was developed (Fig. 2). • Case studies to illustrate and expand the framework were prepared:

o Risk assessment of the Oppstadhornet slope o Risk assessment of offshore geohazards at Ormen Lange (especially slope instability).

• The components of the framework were studied and documented in detail: o Probabilistic stability analysis for individual slopes in soil and rock o Literature study on landslide hazard zonation o State-of-the-art on seismic hazard analysis with emphasis on ground motion models o Literature study on vulnerability in relation to risk management of natural hazards and

elements at risk o Literature review of acceptable and tolerable risk and considerations of societal

aspects and comparison of risk curves (f-N curves) for 8 countries.

Data Collection

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Risk Assessment(Risk Analysis +Risk Evaluation)

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Figure 2 Generalized Integrated Risk Assessment Framework (GIRAF)

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