PARSAN………Subsurface Utility Engineering & Geophysical Investigations

Presented at: Geospatial World Forum  2011, Hyderabad

Presented by: Dr. Sanjay Rana, Director, PARSAN Overseas (P) Limited

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Outline of the Presentation

• About PARSAN

• About SUE

• Geophysical Subsurface Investigations– Seismic Refraction– Ground Penetrating Radar– Electrical Tomography

• Case Study

• Conclusions

About PARSAN……

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PARSAN Overseas

• An ISO 9001:2000 certified geophysical company having international associations for access to latest technology with:

– M/s TerraDat, UK– M/s Radar Systems Inc., Riga– M/s T&A Survey, Netherlands– Landtech Enterprises SA & Earth Research (UK) Ltd

• Recognized as a leader in region for launching new technology. Responsible for launch of:

– Ground Penetrating Radar Technology- 1996– Shear Wave Seismic Refraction- 1997– High Resolution Seismic Tomography- 1998– Inclusion of GPR as mandatory survey before trench less projects- 2001 – Passive Seismic Tomography for Oil Exploration- 2008– Innovative use of geophysical methods for high resolution non-destructive testing of dams

• Highly experienced and trained staff.

• Working in India, Singapore, Oman, Afghanistan, Greece, Saudi Arabia, Bahrain, Kuwait, Iran, Algeria, Georgia…….

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About Speaker

• Professional Geophysicist, with 20 years of work experience. Gold Medalist, University of Roorkee (Now IIT-Roorkee)

• Pioneered use of GPR in India in 1996.

• Have conducted 28 training programs on GPR for various companies in 4 countries.

• Experienced of working with most of the available GPR models like GSSI, Mala, Sensor & Software, Pipe Hawk, and Zond. Overseas GPR experience- Canada, Singapore, Saudi Arabia, Oman, Afghanistan and Bahrain.

• Conducted first ever city level utility mapping project for city of Tirupur, way back in 1999.

• Various Papers & Publications, including “Advanced Technologies for Preparation of Utility Maps of Cities”, which initiated many projects in India.

• Expert panel members of various organizations.

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About SUE……

Existing Underground Utilities are the Veins and Arteries of our

Cities and Roads

And yet, we know very little about where they are

CommunicationGas

PetroleumSewerageDrainage

PowerWater

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WHY?

• Expansion

• Modernization

• Changing Utility

Technology

• Changing Facility

Missions

• Referenced to

changed topo

features

• No centralized

records storage

• No standard format

• No responsibility

We keep adding and changing utilities

We don’t keep good records

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Where do we get Utility Info?

• Visual Observation

• Field Survey

Old Project Plans (As-Designed)Old Project Plans (Red-Lined)

Utility Records (As-Designed)Utility Records (As-Built)

Maintenance RecordsRepair Records

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The Engineer uses these sources to compile a utility composite that overlays the

new design

Nowadays, we frequently digitize this data into a CADD

or GIS System…

This can result in even more errors

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The Engineer ends up with utility data of unknown reliability

This makes it extremely difficult to

manage the risks that are created by existing underground utilities

I think the gas line is here, but I’m not really sure. It might be in conflict with this proposed

piling.

I guess we’ll let the contractor worry

about that !

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What are these Risks?

Utility Damages

Affecting the Safety ofConstruction crews, or

the Public

The Telecommunicationsand other industries

recognize this

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There are a lot of other risks too

• Redesign costs

• Higher construction

bids

• Change orders

• Extra work orders

• Construction Claims

• Higher insurance costs

• Higher financing costs • Bad publicity

Money TIME

Intangibles

Project delaysDetours

Fortunately, there’s a way

to handle this risk

SUBSURFACE UTILITY ENGINEERING

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S.U.E. Combines Traditional Engineering Practices, such as …..

Utility Records Research Relocation Cost Estimates

Utility Design/Relocation Design Plotting of Utilities from Records

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with New Technologies

Utility Designating via

Surface Geophysical Methods

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Utility LocatingVia Non-DestructiveVacuum Exposure

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The Most Significant Advancement is the Utility Quality Level Attribute

Quality Level Attributes are attached to plotted utilities

They indicate how utility data was developed

Reliability and Accountability are defined

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“Quality Level D”

• Plotted on plans from records.

• Sometimes a field visit - to look for utility

indications on the site - is made.

• Sometimes “verbal recollections” are plotted.

The least reliable utility data

This level of effortis great for Project Planning purposes, utility “inventories,”and very preliminary utility relocation cost estimates

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• Surface Appurtenances are surveyed and accurately plotted on

a current site plan

• Utility data from records (QL D) are correlated to the

appurtenances

“Quality Level C”The “traditional” utility depiction

Problems with records interpretations still exist:

e.g. schematics, no appurtenances depicted,

utilities not straight between appurtenances, no records exist, and so

on.

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• Surface Geophysical Methods used to search for and trace

existing utilities.

• Designated utilities are then surveyed and plotted on site plan.

“Quality Level B”

Non-recorded utilities found. Utilities’ routes between

appurtenances are imaged.

Typically used in early preliminary design for construction footprint

decisions.

A significant upgrade in quality

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• Utilities exposed via non-destructive air-vacuum means

• Exposed utilities are then surveyed and plotted on site plan

Elevations, Size, Condition, Materials, Precise Horizontal

Positions are measured and documented

“Quality Level A”

Typically used in final design stages. Allows small

adjustments in design for big savings in construction

A guarantee in 3-D

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QL A and QL B upgrades have been successful in reducing risk on tens of thousands of infrastructure projects.

This is a tried and trueprocess

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Yet, SUE has not been used as a professional standard practice in some areas for many reasons.

• No concerted local or regional effort to educate project owners or engineers of benefits

• Lack of interest by agencies

• Development of SUE has been primarily in developed countries

• Few providers

• Lack of a well defined standard of care created little incentive for changing the status-quo

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A January 2000 FHWA / Purdue University study (Publication No. FHWA-

IF-00-014) states the following:

“A savings of $4.62 for every $1.00 spent on SUE was quantified from a total of 71 projects. These projects had a combined construction value in excess of $1 billion. The costs of obtaining Quality Level “B”

(QL B) and Quality Level “A” (QL A) data on these 71 projects were less than 0.5 percent

of the total construction costs, and it resulted in a construction savings of 1.9

percent over traditional Quality Level C (QL C) and/or Quality Level D (QL D) data.” .62 for

every $1.00 spent on SUE

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One individual project had a $206.00 to $1.00 return on investment (North Carolina DOT).

The simple conclusion of this study is that SUE is a viable technologic practice that reduces project

costs related to the risks associated with existing subsurface utilities and, when used in a systematic

manner, will result in significant quantifiable and qualitative benefits.

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Geophysical Subsurface Investigations……

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Why Use Geophysics…….

• Low Cost

• Rapid Coverage

• No Exposure to buried hazards

• Non Destructive

• Minimal Surface Disturbance

• Easy to integrate

• Integrated capability

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Geophysics- Huge ROI...

• Detailed investigation of site…Saving huge costs towards changed

plans, project delays when surprises crop up….

• No drilling, No digging…Vast information at fraction of cost of traditional

methods.

• Early stage application…Better planning, smooth execution.

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Method Sensitive To... Typical Applications

Seismic RefractionChanges in strata type (soil, weathered rock, rock), rock quality (jointed, weathered), elastic properties

Rock interface, overburden mapping, rock quality, degree of weathering/ jointing, faults, fracture mapping

Resistivity ImagingMoisture content variations, conductivity, water table, porosity

Soil-rock profile, water table determination, weak zone delineation, detection of weak zones under rock interface, buried channels.

ReMi (Refraction Micro-tremor) Change in shear properties of mediumDetermination of shear wave profiles (to determine liquefaction potential, earthquake response)

Crosshole/ downhole/ upholeDifference in elastic properties. Variations in S Wave or P Wave velocity.

Detailed analysis to obtain P and S wave velocities with depth for dynamic moduli: Poisson’s Ration, shear modulus, bulk modulus, Young’s modulus

Seismic ReflectionDifference in acoustic impedance (velocity x density)

Detects interfaces, maps faults/ fractures/ water lenses/ shear zones along tunnel routes

Ground Penetrating Radar Change in dielectric properties

Detection of buried pipes and cables, with exact location and depth. Also used for inspection of concrete structures.

Micro Gravity Changes in Density of Subsurface Detection of buried voids/ cavities

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Seismic Refraction…….

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Basic Principle……..

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Energy Sources……

• Explosives

• Sledge Hammer

• Weight Drop

• Buffalo Gun

• Etc……….

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Recorded Data……

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Velocity Model…….

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Velocity Model…….

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Seismic Refraction- Applications

• Bedrock profile, rock quality and depth.

• Thickness of overburden

• Fractures and weak zones

• Topography of ground water

• Rippability assessment in mines

• Slope stability studies

• Pipeline route studies

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Ground Penetrating Radar…..

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Basic Principle………

Photographs: Georadar Inc.

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How an image is formed………

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Hyperbola Formation………

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Field Example- Pipes………

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Depth Determination………

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Equipment………

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Field Operation………

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GPR- Features………

• Penetration of more than 40 meters in certain formations

(penetration dependent on conductivity and frequency of

antenna)

• Data acquisition at walking speed.

• Identification of objects measuring on few centimeters.

• Light portable equipment

• Results available immediately

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Pavement Assessment…

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Rebars…….

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Rebar Layers……

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Road Subsidence…..

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Cavity……

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Fractures……

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Electrical Tomography…..

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What for……

Applications:

• Determine the underground water resources

• Bedrock quality and depth measurements

• Mineral prospecting

• Dam structure analysis

• Landfill

• Contamination source detection

Advantages:

• Excellent 2-dimensional display of ground resistivity.

• Delineation of small features like cavity, contamination plumes, weak zones in structures like dams etc.

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Example……

Photo Courtesy: www.mragta.com

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Example……

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Cave/ Cavity……

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Boulders……

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Contamination…….

Case Study

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Problem…….

• Project site was for cable stayed bridge across a river.

• A cavity was detected in otherwise massive sandstone, while

drilling.

• It was of utmost importance to determine nature and extent of

this cavity before finalizing the design.

Investigations:

• Geophysical investigations consisting of crosshole seismic and

electrical tomography were conducted to determine depth and

extent of the cavity.

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Results…….

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Conclusions……….

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Conclusions…….

• SUE- Need of the hour for Utility Data Management

• Geophysical Techniques- Quick assessment of subsurface

conditions in non-destructive manner

• Geophysical Techniques- Detailed and continuous information

as against drilling

• Geophysical Techniques- Eliminates surprises during project

execution

Thanks for your attention

Dr. Sanjay Ranasanjay@parsan.biz