1 integrated geophysical approach for rapid & cost effective site investigations for water...
TRANSCRIPT
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Integrated Geophysical Approach for Rapid & Cost Effective Site Investigations for Water Resources
Presented at: India Water Week- April 8-12, 2013
Presented by: PARSAN Overseas (P) Limited
About PARSAN……
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PARSAN Overseas
• An ISO 9001:2008 certified geophysical company
• Promoters recognized as leaders 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– 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.
• Offices in Delhi, Kolkata, Bahrain, Egypt (agent) & Sudan (agent).
• Work experience in India, Singapore, Oman, Afghanistan, Greece, Saudi Arabia, Bahrain, Kuwait, Iran, Algeria, Georgia…….
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About Speaker
• Professional Geophysicist, with 22 years of work experience. Gold Medalist, University of Roorkee (Now IIT-Roorkee)
• Member of various working committees for development of Code of Practices and Standards.
• Completed geophysical investigations of 72 hydro power projects.
• Have conducted 28 training programs on Geophysics for various companies in 4 countries.
• Successfully used integrated geophysical approach for investigations across flowing rivers & for dam safety
• Conferred Golden Achievement Award 2011.
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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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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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Example……
Photo Courtesy: GeoInvest
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Water Well Planning……
Photo Courtesy: GeoInvest
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Water Table Contamination……
Time-lapse monitoring
Photo Courtesy: GeoInvest
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3D Modeling……
Photo Courtesy: GeoInvest
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Detection of soft zone under rock (Hydropower)……
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Cave/ Cavity……
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Contamination…….
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River Crossings…….
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River Crossings…….
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River Crossing……
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River Crossing- Shear Zone…….
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River Bottom Profile…….
Photo Courtesy: GeoInvest
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Seismic Refraction…….
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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 • Seismic velocity increases markedly from unsaturated to
saturated zone.• The acoustic velocity of a medium saturated with water is
greatly increased in comparison with velocities in the vadose zone. Thus, the refraction method is applicable in determining the depth to the water table in unconsolidated sediments.
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Ground Penetrating Radar…..
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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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Water Table Mapping…….
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Water Table Mapping…….
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Fractures……
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GPR- Contaminant Hydrogeology & Soil Stratigraphy
GPR is extremely sensitive to variations in water content. It has been widely used to map water tables and the corresponding stratigraphy that controls groundwater flow. In addition, GPR is very sensitive to changes in water chemistry, particularly soluble inorganic materials that change conductivity. Inorganic materials such as DNAPL (chlorinated solvents) can alter the groundwater distribution resulting in GPR detectable responses.
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Dam Investigations
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Electrical Resistivity Imaging- Dam Axis………
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Electrical Resistivity Imaging- Dam Axis………
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SP Anomaly due to leakage………
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Dam Investigation (integrated with SP)…….
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Ground Penetrating Radar
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GPR- Submerged Area
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GPR-Tomography
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Seismic Tomography
• Acoustic Waves Travel Time• Properties for Each Cell• Colour Tomogram of Dam• Weathered Concrete, Fractures• Highly Detailed Information
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Pipeline Leak Detection…..
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Pipeline Leak Detection using Seismograph…….
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Leak Detection using GPR………
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Leak Detection using GPR ………
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Leak Detection using GPR ………
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Leak Detection using GPR ………
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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…….
• 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
