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Rock EngineeringRock EngineeringPractice & DesignPractice & Design

Lecture 1: Lecture 1: IntroductionIntroductionIntroductionIntroduction

1 of 30 Erik Eberhardt – UBC Geological Engineering ISRM Edition

Author’s Note:Author’s Note:The lecture slides provided here are taken from the course “Geotechnical Engineering Practice”, which is part of the 4th year Geological Engineering program at the University of British Columbia (V C d ) Th k i i d (Vancouver, Canada). The course covers rock engineering and geotechnical design methodologies, building on those already taken by the students covering Introductory Rock Mechanics and Advanced Rock Mechanics Rock Mechanics.

Although the slides have been modified in part to add context, they of course are missing the detailed narrative that accompanies any l l d h h l lecture. It is also recognized that these lectures summarize, reproduce and build on the work of others for which gratitude is extended. Where possible, efforts have been made to acknowledge th v ri us s urc s ith list f r f r nc s b in pr vid d t th the various sources, with a list of references being provided at the end of each lecture.

Errors, omissions, comments, etc., can be forwarded to the


Errors, omissions, comments, etc., can be forwarded to the author at: [email protected]

Course OverviewCourse OverviewThis course will examine different principles, approaches, and tools used in geotechnical design. The examples and

hi t i i d ill f case histories reviewed will focus primarily on rock engineering problems, although many of the analytical and numerical techniques reviewed are also numerical techniques reviewed are also used in other areas of engineering.

Rock engineering design has largely evolved from different disciplines of applied mechanics. It is a truly interdisciplinary subject, with applications in geology and geophysics, mining, petroleum and geotechnical engineering.


Course OverviewCourse OverviewWhat makes geotechnical engineering unique is the complexity and What makes geotechnical engineering unique is the complexity and uncertainty involved when interacting with the natural geological environment.

Rock masses are complex systems!

Often, field data (e.g. geology, geological structure, rock mass properties, groundwater, etc.) is limited to surface observations and/or


properties, groundwater, etc.) is limited to surface observations and/or limited by inaccessibility, and can never be known completely.

Deep TunnelsDeep Tunnels

Gotthard Base-Tunnel (CH)

Cost = $7 billion (and counting)Time to build = 12+ yearsLength = 57 km Length = 57 km Sedrun shaft = 800 m Distance between parallel tubes = 40 m Excavated material = 24 million tonnes

0) e

t al

.(20

00


Loew

Deep Tunnels Deep Tunnels –– Importance of GeologyImportance of Geology

Weak rock under high stresses may lead to squeezing ground conditions, which may result in damage/failure to the ground support system or require the costly re-excavation system, or require the costly re excavation of the tunnel section.

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t

In strong brittle rock, high stress conditions may lead to rockbursting (the sudden release of stored strain energy). Bursts manifest themselves through


strain energy). Bursts manifest themselves through the sudden ejection of rock into the excavation.

Deep Open PitsDeep Open PitsChuquicamata (Chile)

Classification = open pit copper mine.Pit size = 4,500m long, 3,540m widePit depth = 800m (1100m by 2014)Pit depth = 800m (1100m by 2014)Production = 650,000 metric tons/yearOre grade = 1.1% Cu


Deep Open Pits Deep Open Pits -- Complex Complex InteractionsInteractionsFinsch Mine, South Africa

(Flores & Karzulovic, 2002)

Numerous mining operations are considering the move to underground in order to mine deeper resources h it th i d when open pits near their end.

However, our body of practical knowledge related to the impacts of underground mining on the surface

i t i li it d i t d i environment is limited, introducing economic risks to the mine and safety risks to mine personnel.

P l b S th Af i


Palabora, South Africa(Moss et al., 2006)

Hydroelectric ProjectsHydroelectric Projects

)et

al.

(200

4)Th

uro

e

Nathpa Jhakri Hydroelectric Project (India)

Estimated cost = $2 billionDam = 60.5 m concrete gravity damCapacity = 1500 MWConstruction = began in 1993 (was to take 5 years) Status = 4 units running 2 still to be completed


Status = 4 units running, 2 still to be completedBoasts = largest & longest headrace tunnel in India

Hydroelectric Hydroelectric Projects Projects –– Rock Mass InteractionsRock Mass InteractionsWE WE

Creepingrock mass4000

M.a.s.l.

SatlujH

Typical majorrock slide (Fig.2)

Foliation (quartz-mica-schists and related

Stress

3000

2000

UPHILLDeformation ofrock mass undercompression / tensionstress

h

Tunnel

ated rock types)field

2000

1000

Spallingof rock materialand shotcrete

Bucklingof steel ribs

Sheardeformation

field

11,5 m

0 m1000200030004000 1000

04)

Cracks inshotcrete lining

Foliation (quartz DOWNHILL

11,5

m

ro e

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.(20

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tz-mica-schist)

DOWNHILL

Thur

Rock as an Engineering MaterialRock as an Engineering Material

A common assumption when dealing with the mechanical behaviour of solids is that they are:that they are:

· homogeneous · continuous · isotropic

However rocks are much more complex

isotropic

However, rocks are much more complex than this and their physical and mechanical properties vary according to scale As a solid material rock is often: scale. As a solid material, rock is often:

· heterogeneous · discontinuous · anisotropic


anisotropic

Rock as an Engineering MaterialRock as an Engineering Material

sandstone strength

Homogeneous Continuous Isotropic

sandstoneequal in

all directions

Heterogeneous Discontinuous Anisotropicshale

Heterogeneousfault

Discontinuoushighstrength

varies withdirection low

Anisotropic

sandstone joints


Rock as an Engineering MaterialRock as an Engineering MaterialTh k f t th t di ti i h k i i f th The key factor that distinguishes rock engineering from other engineering-based disciplines is the application of mechanics on a large scale to a pre-stressed, naturally occurring material.

Hoek’s GSIClassification intact

rock

rock mass ground response

fractured


fracturedrock

Influence of Geological FactorsInfluence of Geological Factors

In the context of the mechanics problem, we should consider the material and the forces involved. As such, five primary geological factors can be viewed as influencing a rock mass.

We have the intact rock which is itself divided by discontinuitiesto form the rock mass structure. to form the rock mass structure.

We find then the rock is already subjected to an in situ stress.

Superimposed on this are the influence of pore fluid/water flow and time.

With all these factors, the geological history has played its part, altering the rock and the applied forces.


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Influence of Geological Factors Influence of Geological Factors –– Intact RockIntact Rock

The most useful description of the mechanical behaviour of intact rock

992)

is the complete stress-strain curvein compression.

ner

et a

l.(1

9

From this curve, several features of interest are derived:

Lock

n

derived:

· deformation moduli (E, )· brittle fracture parameters D

amag

e,

AE

cohesion Relative C

al.(

1999

)

brittle fracture parameters· peak strength criteria· the post-peak behaviour

Cum

ulat

ive

D

damage

Cohesion

erha

rdt

et a

l


Normalized Stress (/cd) Ebe

Influence of Geological Factors Influence of Geological Factors –– Intact RockIntact Rock

7)

Strength, or peak strength, is the maximum stress, usually averaged over a plane, that the rock can sustain. After

arri

son

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7

it is exceeded, the rock may still have some load-carrying capacity, or residual strength.

Hud

son

& H

aH

high stiffnesshigh strength

medium stiffnessmedium strength

low stiffnesslow strength

low stiffnesslow strength


very brittle med. brittleness brittle ductile

Influence of Geological Factors Influence of Geological Factors -- DiscontinuitiesDiscontinuitiesDiscontinuities such as faults and joints may lead to structurally-controlled instabilities whereby bl k f th h th blocks form through the intersection of several joints, which are kinematically free to fall or slide from the excavation periphery slide from the excavation periphery as a result of gravity.

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5


Hoe

k

Influence of Geological Factors Influence of Geological Factors –– In SituIn Situ StressStressWhen considering the loading conditions imposed on the rock mass, it must be recognized that an in situ pre-existing state of stress already exists in the rock.

In the case of an underground excavation, such as a mine or tunnel no such as a mine or tunnel, no new loads are applied but the pre-existing stresses are redistributed.

989)

back

et a

l.(1

Total = In Situ + Excavation-Stress Stress Induced Stress

Zob


Stress Stress Induced Stress

Influence of Geological Factors Influence of Geological Factors –– In SituIn Situ StressStress

99)

tin

et a

l.(1

9


Mar

t

Influence of Geological Factors Influence of Geological Factors –– In SituIn Situ StressStress

StSt

1

Unstable

Stable

StressStressConcentrationConcentration

WedgeIn-Situ Stress 00

)

Stress PathRelaxationRelaxation

In Situ Stress

er e

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3 Kais

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Influence of Geological Factors Influence of Geological Factors –– GroundwaterGroundwater

Many rocks in their intact state have a very low permeability compared to the duration of the engineering construction, but the main water flow is

ll i d m bilit ( j i t ) Th usually via secondary permeability (e.g. joints). Thus the study of flow in rock masses will generally be a function of the discontinuities, their connectivity and the hydrogeological environment.y g g

A primary concern is when the water is under pressure, which in turn acts to reduce the effective stress and/or induce instabilities. Other aspects such as groundwater aspects, such as groundwater chemistry and the alteration of rock and fracture surfaces by fluid movement may also be of concern.


Rock Engineering DesignRock Engineering Design

Given the large scale of many of these projects, there is considerable economic benefits in designing these structures in the optimal

way.

In practice it quickly In practice, it quickly becomes evident that one ignores rock mechanics principles and rock p pengineering experience at considerable physical and financial peril.


Integrated Risk AssessmentIntegrated Risk Assessmentse

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Laca

ssD

üzg


Site Investigation & Data CollectionSite Investigation & Data Collection

l i l d l

Geophysical investigations

Geological investigations

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.(2

008)

Rockmass

geological model

Will

enbe

rg e

t

processesW


Site Investigation & Data CollectionSite Investigation & Data Collection

l i l d l

Geophysical investigations

Geological investigations

Rockmass

geological model

processes

St bilit

failure kinematics

Geotechnical Stabilityanalysis

Controllingmechanism(s)

Geotechnical monitoring


m m( )Willenberg et al. (2008)

Design MethodologyDesign MethodologyS f l i i d i i l d i hi h i Successful engineering design involves a design process, which is a sequence of events within which design develops logically. Bieniawski (1993) summarized a 10 step methodology for rock engineering design problems, incorporating 6 design principles: p , p g g p p

Statement of the problem

Step 1:p

performance objectives

Functional requirements and

constraints

Step 2:

3)

Design Principle 1: Clarity of design objectives and ia

wski

(199

3


g jfunctional requirements. Bi

en

Design MethodologyDesign MethodologyBi ni ski (1993)Statement of the problemStep 1:

performance objectives

Design Principle 1: Clarity of design objectives and functional requirements

Bieniawski (1993)

Functional requirements and constraints

Step 2:functional requirements.

design variables & d i idesign issues

Collection of informationStep 3:geological characterization,

Design Principle 2: Minimum uncertainty of geological

conditions.g g ,rock mass properties, in situstresses, groundwater, etc.

Concept formulationStep 4:D i P i i l 3

Analysis of solution Step 5:

design variables & design issues

Design Principle 3: Simplicity of design

components (e.g. geotechnical model).


ycomponents

Step 5 ( g g )

Step 5:

l l l

Design Principle 3: Simplicity of design

t

Analysis of solution components

observational, analytical, empirical, numerical methods

Synthesis and specification Step 6:

components.

Design Principle 4: State of the art practice.y p

for alternative solutionsStep 6

shapes & sizes of excavations, rock reinforcement options and associated safety factors

D i P i i l 5

EvaluationStep 7:

consideration of non-rock OptimizationStep 8:

performance

Design Principle 5: Optimization of design (through evaluation of

analysis results, monitoring, engineering aspects (ventilation, power supply, etc.)

passessment

ana y r u t , m n t r ng, etc.).

RecommendationStep 9:feasibility study

Design Principle 6: b l ( h

lessons learned

- feasibility study- preliminary & final designs

ImplementationStep 10:

Constructability (can the design be implemented safely and efficiently).

Bi i ki (1993)


efficient excavation & monitoring

Bieniawski (1993)

Lecture ReferencesLecture ReferencesBieniawski, ZT (1993). Design methodology for Rock Engineering: Principles and Practice. InComprehensive Rock Engineering: Principles, Practice & Projects. Pergamon Press, Oxford, 2: 779-793.

Düzgün, HSB & Lacasse, S (2005). Vulnerability and acceptable risk in integrated risk assessmentframework. In Landslide Risk Management. A.A. Balkema: Leiden, pp. 505-515.

Eberhardt, E, Stead, D & Stimpson, B (1999). Quantifying pre-peak progressive fracture damagein rock during uniaxial loading. International Journal of Rock Mechanics and Mining Sciences 36(3):361-380.

Flores G & Karzulovic A (2002) Geotechnical guidelines for a transition from open pit toFlores, G & Karzulovic, A (2002). Geotechnical guidelines for a transition from open pit tounderground mining. Benchmark report. Project ICS-II, Task 4.

Hoek, E, Kaiser, PK & Bawden, WF (1995). Support of Underground Excavations in Hard Rock.Balkema: Rotterdam.

Hudson, JA & Harrison, JP (1997). Engineering Rock Mechanics – An Introduction to the Principles .Elsevier Science: Oxford.

Kaiser, PK, Diederichs, MS, Martin, D, Sharpe, J & Steiner, W (2000). Underground works inhard rock tunnelling and mining. In Proceedings, GeoEng2000, Melbourne. Technomic Publishing:g g g , g , gLancaster, pp. 841-926.

Lockner, DA, Byerlee, JD, Kuksenko, V, Ponomarev, A & Sidorin, A (1992). Observations ofquasistatic fault growth from acoustic emissions. In Fault mechanics and transport properties ofrocks. Academic Press: San Diego.


g

Lecture ReferencesLecture ReferencesLoew, S, Ziegler, H-J & Keller, F (2000). AlpTransit: Engineering geology of the world’s longesttunnel system. In: Proceedings, GeoEng 2000, Melbourne. Technomic Publishing: Lancaster, pp. 927–937.

Martin, CD, Kaiser, PK & McCreath, DR (1999). Hoek-Brown parameters for predicting the depthof brittle failure around tunnels. Canadian Geotechnical Journal 36(1): 136-151.

Moss, A, Diachenko, S & Townsend, P (2006). Interaction between the block cave and the pitslopes at Palabora mine. Journal of The South African Institute of Mining and Metallurgy 106: 479-484.

Thuro, K, Eberhardt, E & Gasparini, M (2004). Deep seated creep and its influence on a 1.5 GWhydroelectric power plant in the Himalayas. Felsbau 22(2): 60-66.

Willenberg, H, Loew, S, Eberhardt, E, Evans, KF, Spillmann, T, Heincke, B, Maurer, H &Green AG (2008) Internal structure and deformation of an unstable crystalline rock mass aboveGreen, AG (2008). Internal structure and deformation of an unstable crystalline rock mass aboveRanda (Switzerland): Part I - Internal structure from integrated geological and geophysicalinvestigations. Engineering Geology 101(1-2): 1-32.

Zoback, ML, Zoback, MD, et al. (1989). Global patterns of tectonic stress. Nature 341(6240):291 298291-298.


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