INTRODUCTION
Laboratory investigation has been conducted on different rock types from soft sedimentary to strong igneous to study their strength behaviour, physical properties, seismic wave velocities, electrical resistivity and Schmidt rebound numbers etc. The results have been examined to understand the nature of relationships existing between rock strengths and these characteristics. Good correlations have been found to exist between them implying potential use of such correlations for preliminary estimation of in-situ rock strengths from certain easy to conduct, rapid and non-destructive tests data.
A number of civil engineering projects such as hydroelectric power works, underground tunnels, bridges etc. are fast coming up in Himalayan regions and many more such projects are envisaged in near future. For these projects, located in difficult terrain and seismically active region, large area needs to be explored to understand nature and behaviour of rocks and rock formations likely to be influenced due to proposed structures.
The rock strengths are the governing factors in planning and design of structures resting on or within the rock mass. The reliability of strength parameters determined through in-situ tests at the site are no doubt very high. However, these tests at times are not justifiable for large area coverage due to technical feasibility, prohibitive cost and time constraints. Thus it becomes imperative to conduct appropriate tests in the laboratory on representative rocks procurred from the project site and interprete the results to estimate their field behaviour. Alternatively,. non-destructive geophysical field methods, v?z. seismic refraction, electrical resistivity etc. which are not only rapid and cost effective but provide subsurface informations at desired depths & locations and ideally suit for large area coverage can be used. Similarly, Schmidt rebound hammer is the simplest non-destructive test suitable for rock surface exploration, the results of which may serve as rock strength index.
The estimation of in-situ rock strengths from field data of geophysical soundings at different depths or at surface from Schmidt hammer test results will be possible provided correlations between strengths and properties namely compressional & shear wave velocities, electrical resistivity, Schmidt rebound number etc. if exists, should be known. In this context, herein an attempt has been made to examine the above possibility for rocks ranging from very soft sedimentary to strong ingeous.
