Dr. Sanjay Rana, Ashutosh Kaushik, Bhaskar Chendhoor (PARSAN Overseas Pvt Limited)
[email protected]

About Parsan

• An ISO 9001:2015 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- 1998
• Highly experienced and trained staff.
• Offices in Delhi, Kolkata, Bhopal, Bahrain, Saudi Arabia, Singapore
• Work experience in India, Nepal, Bhutan, Saudi Arabia, Bahrain, Kuwait, Oman, Afghanistan, Singapore, Greece, Iran, Algeria, Georgia…

About Speaker (Dr. Sanjay Rana)

• Professional Geophysicist, with 32 years of work experience. Chairman AF Academy & Managing Director, PARSAN, An engineering geophysics company
• Gold Medalist- 1990, University of Roorkee (Now IIT-Roorkee)
• Pioneered use of Near Surface Geophysics (Private Sector) in India in 1995.
• Pioneered use of Dam Geophysics in India in 1998.
• Successfully used integrated geophysical approach for investigations across flowing rivers & for dam safety
• Completed geophysical investigations of 72 hydro power projects.
• Member of various working committees for development of Code of Practices and Standards, including BIS, IRC.
• Principal author of:
  • Guidelines on Geophysical Investigation of Dams
  • Guidelines for Geophysical Investigation of Tunnels (TAI)
  • Guideline for Geophysical Investigations for Bridges (IRC)
  • Indian Code for Subsurface Utility Mapping.

The Engineers first problem in any design situation is to discover what the problem really is.  

Difficult Ground Conditions?

• 1) Expertise & engineering solutions available for dealing with any (almost) ground condition
• 2) The problem is meeting the unexpected and uncertainty of ground conditions

Geophysical Investigation for Dam Sites…

• Study available geological maps
• Geological Mapping
• Geophysical Investigations
• Drilling (with geophysical logging)
• Slope stability analysis
• Hydrogeological studies
• Seismicity Study
• Burrow Areas

Necessary Investigation Steps…

• Different types of geophysical studies should be performed in the dam site and reservoir area to indicate the following data:
• To indicate groundwater level.
• To indicate the mechanical properties of the rocks and the depth of the weathering zone.
• To detect faults/ fractures/ shear zones/ weak zones
• To investigate burrow areas
• To conduct slope stability studies
• To determine shear wave velocities for seismic hazard studies

Dam Site Investigations – Advanced Geophysics….

• Seismic Refraction Tomography- bed rock profile, fault/ fracture/ shear zones.
• Resistivity Imaging- detailed subsurface images even in velocity inversion zones
• ReMi/ MASW- Shear wave profile from surface surveys, without any boreholes
• Crosshole/ uphole/ downhole surveys- P&S wave velocities for detailed analysis of various layers and dynamic moduli.
• Crosshole/ uphole/ downhole surveys- P&S wave velocities for detailed analysis of various layers and dynamic moduli.
• Seismic Reflection- tunnel route investigation
• Electrical Resistivity- Earth Grid Design

Dam Site Investigations- Advanced Geophysics….

• Seismic Refraction Tomography- bed rock profile, fault/ fracture/ shear zones.
• Resistivity Imaging- detailed subsurface images even in velocity inversion zones
• ReMi/ MASW- Shear wave profile from surface surveys, without any boreholes
• Crosshole/ uphole/ downhole surveys- P&S wave velocities for detailed analysis of various layers and dynamic moduli.
• Crosshole/ uphole/ downhole surveys- P&S wave velocities for detailed analysis of various layers and dynamic moduli.
• Seismic Reflection- tunnel route investigation
• Electrical Resistivity- Earth Grid Design

Limitations & Reasons for Failures?

• Wrong tool selection
• Method lacking desired resolution
• Geology ignored
• Calibration ignored
• Only single tool used
• Wrong initial model

Understanding Tomography…

Conclusion:

 Geological investigations and site characterization by making drifts has been a standard procedure for large dams. This provides very valuable information about dam site. Making drifts is a time consuming and expensive activity. To gain more advantage and cover more area, conducting seismic tomography between drifts is a cost-effective option.