Many researchers have used geophysical methods in their geotechnical investigations 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33. Therefore, a relievable approach is necessary which can determine the geotechnical parameters, reduce an extensive number of drilling tests, and bring a sigh of relief to the planners. Using the traditional geotechnical approaches, it is a difficult task for the planners to obtain an accurate geological model for the engineering structure design. Hence, the rock mechanical parameters are hard to obtain from the frequent boreholes. In most cases, the drilling tests of large sites fail to meet the needs of engineers 19. Besides, such approaches are costly and time consuming, and require more equipment 18. The borehole tests provide limited coverage of the vertical measurements along some specific points only, cannot evaluate the subsurface laterally, and are hardly conducted in the steep topographic areas 2, 17. The rock mass quality parameters, however, are conventionally determined by the rock core samples obtained from the boreholes 1, 5, 7, 14. These parameters are widely used to classify the bearing strength of the engineering rock mass 16. Rock mass integrity coefficient (Kv), rock quality designation (RQD), volume joint number of rock mass (JV) and average joint spacing (dP) are the main geotechnical indices to determine general stability of the subsurface rock mass 10, 11, 12, 13, 14, 15. The geotechnical sites are investigated for the evaluation of engineering rock quality and fractures/faults 6, 7, 8, 9. Thus, a thorough investigation of the subsurface rocks is essential to obtain an accurate geological model for the success of foundation design.

The failure of engineering infrastructures is mostly caused by the weak bearing capacity of foundation rocks 5. The bearing strength of these rocks depends on various factors, such as type of rock, weathering degree, mineralogical composition, rock association, faults/fractures, rock deformation and water infiltration etc 3, 4. In hard rock terrains, successful construction of the engineered structures mainly relies on bearing capacity of the foundation rocks 1, 2. Rock mass quality evaluation is a challenging task all over the world.

Our approach is applicable in any hard rock setting, and the established correlations can be used in areas even where no well test exists. Our work proposes that, in case of sparse borehole data, the established empirical equations can be used to determine Kv along different geophysical profiles via 2D/3D insight of the subsurface. Compared with the past geotechnical investigations, our work reduce the ambiguities caused by the inadequate well tests and provide more accurate geological model for infrastructures design. The estimated Kv provides 2D/3D imaging of the rock mass quality evaluation via weathered/unweathered rock and faults detection in order to cover the entire area even where no drilling test exists.

In this work, we establish empirical correlation between ERT and limited drilling data to obtain rock mass integrity coefficient (Kv). Conversely, geophysical methods such as electrical resistivity tomography (ERT) are non-invasive, user-friendly, and fast. However, such tests are expensive and time consuming, provide point measurements, and cannot be conducted in steep topographic areas, and thus cause uncertainties in the geological model. These investigations mainly depend on the traditional drilling tests. Rock mass quality evaluation is a challenging task in geotechnical investigations given the natural heterogeneity and the limited data.

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