Geotechnical and Geophysical Investigations of Estimating Rock Mass Properties

Abstract

Accurate assessments of the deformation and strength properties of rock masses are essential for analysing the foundations, subsurface excavation, and construction of slopes, however, identifying geotechnical properties, particularly weak rock masses, is challenging for geoscientists, geologists, and geotechnical investigators. To determine the rock mass properties, geophysical techniques, and rock mass classification methods are widely used. Although rock classification methodologies exist, they are rarely employed in foundation construction analysis due to being predominantly established for tunnelling purposes. This study aims to employ classification methods, and geophysical and geotechnical investigation approaches to provide realistic rock mass properties for a building foundation, compare results, and assess techniques' effectiveness; it also reviews current state-of-the-art methods for classification techniques and investigations. Results show that compressional and shear wave velocities increase with depth indicating a change from poor to satisfactory mechanical behaviour, and empirical equations provide highly valuable and satisfactory deformation modulus values when compared to field seismic values. Almost all classification methods provided reasonable results compared with the seismic results, however highly overestimated and underestimated outcomes were obtained from some empirical equations applying the Rock Quality Designation index and Rock Mass Rating system. Empirical equations that gave the practical deformation modulus outcomes are the Rock Mass Rating based equations and Q-based equations and Geological Strength Index-based equations. Overall, the Rock Quality Designation index underestimated the seismic result, whereas the Rock Mass Rating, Q, and Geological Strength Index systems produced good agreement and realistic results. To conclude, classification methods were effectively applied to a building foundation. Since the Rock Quality Designation is a key value and feature for other systems including Q, and Rock Mass Rating systems, it is an essential factor. Although the Q systems provided practical consequences, this system mainly relied on the Rock Quality Designation value not the compressive strength of the intact rock. The Rock Mass Rating and being the most feasible and essential systems due to detailed geotechnical observations as inputs more significantly the uniaxial compressive strength of the intact rock, and various factors including deformation modulus, strength, Poisson’s ratio, equivalent cohesion, and friction angle of rock mass as outcomes.