ROLE OF GEOELECTRIC IMAGING IN GEOTECHNICAL SITE INVESTIGATIONS WHEN CONVENTIONAL GEOTECHNICAL TESTS FAIL

Majority of geotechnical site investigations are ideally suited for homogeneous soil masses. However, if inhomogeneous near-surface soils offer high resistance to SPT and other conventional geotechnical tests, it becomes difficult to assess geotechnical characteristics of deeper earth material, where conventional geoelectric imaging could still map the subsurface lithology. But geoelectric imaging results cannot be translated to any quantitative geotechnical test results due to absence of respective transforms. Here, we illustrate our method through a case study at a project site in Indo-Gangetic Alluvial Plains (IGP) close to Siwalik range of Outer Himalaya, India. The method entails in correlation of normalized plots of resistivity and Standard Penetration Test (SPT) results and prediction of SPT results for deeper strata at each borehole site. The predicted SPT results have been successfully used in construction of a major multi-storeyed housing colony in the study region. The accrued results clearly stress that layered earth models often proposed geotechnical engineers for soil masses are not enough in real situations and a conjunctive use of geoelectric imaging and geotechnical test results may address the concerned problems by evolving 2-D and 3-D geotechnical models for near-surface.