1 Dam Geophysics- An Indispensable Tool for Dam Health Check & Dam Monitoring Presented by: Dr. Sanjay Rana, Director, PARSAN

2 PARSAN 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 –Shear Wave Seismic Refraction –High Resolution Seismic Tomography –Passive Seismic Tomography for Oil Exploration –Innovative use of geophysical methods for high resolution non-destructive testing of dams Highly experienced and trained staff. Offices in Delhi, Kolkata, Bahrain, Saudi Arabia, Egypt (agent) & Sudan (agent). Work experience in India, Singapore, Oman, Nepal, Bhutan, Afghanistan, Greece, Saudi Arabia, Bahrain, Kuwait, Iran, Algeria, Georgia…….

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6 Choice of method The user has considerable scope for choice. However, some factors to be considered are: –What type and shape of feature is being imaged? –Is an area or line survey the better? –What physical properties will show the best contrast? –Are there any strong but irrelevant contrasts that will mask the results? –To what depth must the survey penetrate? –What spatial resolution is needed? –What are the time or cost constraints? –Are there any special restrictions eg on access or damage?

7 Dam Investigations

8 Surface only Inspector Dependent Standards?

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10 Why Geophysics for Dams Checks? Most suitable method for regular health checks of dams Early detection of problems Totally non-destructive, extremely suitable for structures like dams Helps design rehabilitation programs better and accurately Helps assess success of rehabilitation measures undertaken Identification of damaged areas inside the body dam Identification of not visible fractures and voids Identification of zones of seepages  More information + Low Cost + Quick

11 Which Technique/ Tool? Objective of Investigation Resolution required Depth penetration required Physical property to be defined Geometry of Dam Nature of target & host material

12 Problem- Leakage/ Seepage? Presence of water/ moisture primarily changes conductivity of dam material.. –Electrical Resistivity Imaging It is also necessary to differentiate between saturated zones and zones through which active seepage/ leakage is taking place. –Streaming Potential Dams crest can have embedded man made objects; pipes, cables etc., and their location must be known to interpret Electrical and SP data. –Ground Penetrating Radar

13 Problem- Water Seepage/ Leakage? Presence of water/ moisture primarily changes conductivity of dam material. –Electrical Resistivity Imaging (ERI) It is also necessary to differentiate between saturated zones and zones through which active seepage/ leakage is taking place –Streaming Potential Dams crest can have embedded man made objects; pipes, cables etc., and their location must be known to interpret Electrical and SP data. –Ground Penetrating Radar

14 Saturated Zones & Active Seepage Zones

15 Problem- Determining Dam Strength? Density of dam material affects the P wave velocities. –Seismic Refraction Tomography Material strength is also defined by S wave velocities –MASW/ ReMi P & S wave velocity information can be used to compute Poisson’s Ration, Bulk Modulus, Shear Modulus, Young’s Modulus Seismic Refraction results can also be used to determine Phreatic line.

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17 Velocity Model- Dam Body…….

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19 Problem- Detailed Analysis of Dam Section? Surface methods to detect dam condition along entire length Detailed information across anomalous zone as a dam section –Seismic Tomography (cross-face or between boreholes) Possible between d/s & u/s face Possible between dam top and gallery

20 Results……

21 SPILLWAY SECTIONS Velocity tomographyDensity tomography

22 SHOULDER SECTIONS Velocity tomographyDensity tomography

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25 When?

26 When do you need to investigate your dam? It is desirable to have a 'base line' data of dam soon after completion of dam. For older dams, this time is 'now'. Before designing rehabilitation plan After carrying out rehabilitation works (to check efficacy) ‘Changes' in physical properties are much easier to interpret than one time measurement values. Under 'normal' conditions, such measurements should be repeated every couple of years as a routine dam inspection program.

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28 Conclusions……. The non-destructive nature of geophysics makes it an ideal tool for health checks of critical structures like dams, where drilling is the last option. Strong cooperation & interaction between geophysicist and dam engineer mandatory for a successful investigation program Choice of the right technique/ tool is critical for success

Thanks for your attention Dr. Sanjay Rana