Determination of rock mass integrity coefficient using a non-invasive geophysical approach

Abstract

Determination of rock mechanical parameters is the most important step in rock mass quality evaluation and has significant impacts on geotechnical engineering practice. Rock mass integrity coefficient (KV) is one of the most efficient parameters, which is conventionally determined from boreholes. Such approaches, however, are time-consuming and expensive, offer low data coverage of point measurements, require heavy equipment, and are hardly conducted in steep topographic sites. Hence, borehole approaches cannot assess the subsurface thoroughly for rock mass quality evaluation. Alternatively, use of geophysical methods is non-invasive, rapid and economical. The proposed geophysical approach makes useful empirical correlation between geophysical and geotechnical parameters. We evaluated the rock mass quality via integration between KV measured from the limited boreholes and inverted resistivity obtained from electrical resistivity tomography (ERT). The borehole-ERT correlation provided KV along various geophysical profiles for more detailed 2D/3D (two-/three-dimensional) mapping of rock mass quality. The subsurface was thoroughly evaluated for rock masses with different engineering qualities, including highly weathered rock, semi-weathered rock, and fresh rock. Furthermore, ERT was integrated with induced polarization (IP) to resolve the uncertainty caused by water/clay content. Our results show that the proposed method, compared with the conventional approaches, can reduce the ambiguities caused by inadequate data, and give more accurate insights into the subsurface for rock mass quality evaluation.