Characterization of elastic wave propagation in jointed rock and rock mass classification using shear waves

Abstract

The information about the state of rock mass is a significant factor to decide its construction method and support pattern, and therefore it is crucial to characterize rock masses reliably for constructing the underground structures. One of the most promising methods for rock mass characterization is using elastic waves. In order to use elastic waves in rock masses, it is necessary to understand the characteristics of elastic wave propagation in rock masses. Therefore, this study characterizes the elastic wave propagation in jointed rock masses and classifies the rock mass using shear wave velocity based on the results. The aim of this thesis is to develop a model for elastic wave velocity and damping; to identify and quantify the effect of stress level and various joint conditions on elastic wave velocity and damping of a jointed rock mass; and to classify a jointed rock mass using shear wave velocity. The models for elastic wave velocity and damping in rock masses are developed. Effective moduli are substituted into the wave equations to derive an effective moduli model for elastic wave velocity in rock masses. The model considers the modulus of intact rock, the joint stiffness, and the spacing between joints. The joint stiffness is expressed as a function of stress and captured by the α and β parameters. The model for elastic wave damping in the equivalent continuum system is developed for rock masses considering that attenuation of intact rock and joints. The intrinsic material loss or damping in an intact rock is not affected by stress level, while the damping in joints is highly affected by stress level. Thus, the damping in joints is expressed as a function of stress by the αD and βD parameters similar to the expression for particulate materials. The rock resonant column testing device is developed to simulate the elastic wave propagation in jointed rock. The device can generate long-wave length wave propagation through the discrete rock discs, so that t...