Evaluation of Engineering Rock Mass Quality via Integration Between Geophysical and Rock Mechanical Parameters

Accurate evaluation of rock mass quality and faults/fractures is the main challenge in rock mechanics and rock engineering. Rock quality designation (RQD) is an important rock mass classification index for infrastructures design. However, the rock mechanical parameters are conventionally acquired from boreholes. Such geotechnical test procedures are time consuming and costly. In addition, drilling approaches need more equipment, suffer topographic constraints, provide geological information only on points in the subsurface, and thus leave uncertainty in the geological models. Our work introduces an empirical based geophysical approach of electrical resistivity tomography (ERT) to obtain rock mechanical parameters essential for foundation design of engineering facilities. The inverted resistivity obtained from ERT was empirically correlated with RQD acquired from the limited drilling tests to assess the entire site for rock mass quality via 2D/3D subsurface mapping of various rocks, including completely crushed rock, relatively crushed rock, poorly crushed rock, relatively integral rock and completely integral rock. The main faults (deep weathered zones) in ERT/RQD models were delineated by low values of these parameters. Our approach can reduce an extensive number of boreholes, and thus bridges the gaps between accurate geological models and the limited well data. Compared with the traditional borehole methods and the past empirical approaches, our work can evaluate the rock mass quality more accurately for successful construction of engineering structures. Our novel approach can be used in most of the weathered terrains, especially in areas, where it is difficult to acquire many core samples. We propose that the established empirical equations are applicable in the sites with similar geological setting, where no borehole exists to obtain RQD.