Geophysical Investigation Methods

Dr Tariq Rahiman

Geophysical techniques, when used in the right circumstances and by people with the right experience and qualifications can deliver valuable information to an integrated site investigation.

Geophysical methods add significant cost and time efficiencies to site investigation programs compared to traditional techniques, providing continuous ground scans and characterizing bulk properties of soil and rock, as opposed to “point” located data from intrusive tests. As geophysical equipment are smaller and mobile, they offer more portability in areas of difficult access and greater operator safety. Moreover, as geophysical surveys are non-intrusive, they have minimal impact on the survey area and are particularly relevant in areas of high environmental and cultural sensitivity.  Geophysics may not be appropriate for every geotechnical problem, however through trialling over a number of years, innovative geophysical survey designs have been developed with a proven track record of supporting ground engineering projects.

This presentation focuses on common geophysical techniques used in ground engineering applications on land, overwater, in boreholes, and during site investigations, construction and for monitoring. The methods described will include seismic (refraction, reflection, MASW, tomography, VSP, cross hole), electrical (2D/3D ERI, Wenner), electromagnetic, microgravity, ground penetrating radar (GPR), various downhole techniques (televiewers, FWS) and non-destructive testing. Typically engineering parameters measured from geophysical tests such excavatibility, small strain moduli, V_s30, electrical and thermal resistivity will be explained. Some case studies will be presented involving karstic/mine void mapping, optimising large SI programs, seepage and stability assessments of TSFs, tunnel and offshore alignment investigations.

Dr Tariq Rahiman Technical Director and Geophysics Practice Area Network Leader, WSP

Tariq has over 24 years’ experience in the practice of geophysical, geological and geotechnical, investigations in Australia, SE Asia and SW Pacific. Close to 17 years of these have been for Golder/WSP’s ground engineering, mining, oil and gas, water and energy client sectors.

Tariq’s main area of expertise is in the application of near-surface geophysical techniques for characterisation of subsurface and includes a variety of near surface geophysical methods such as seismic refraction, seismic reflection, multi-channel analysis of surface waves (MASW), electrical resistivity imaging, frequency-domain electromagnetics, downhole and cross-hole seismic, borehole wireline geophysical logging, ground penetrating radar and marine geophysics. Tariq also has specialist skills in geological mapping for site investigations and geological hazard assessments. He has experience in earthquake source characterisation, numerical modelling and seismic and tsunami hazard analysis.

In his current role as the technical lead of geophysics in Australia, Tariq is responsible for developing the geophysical services, maintaining quality of geophysics deliverables to clients, introducing and integrating innovative geophysical technologies into ground engineering practice, and training and mentoring junior staff. Tariq is also the Geophysics PAN leader and facilitates global collaboration of geophysicists in WSP.

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