Estimating In Situ Deformation of Rock Masses Using a Hardening Parameter and RQD

This study explores the utility of a pressure-dependent empirical hardening parameter in estimating deformation of rock masses. The hardening parameter has drawn poor attention in classical rock mechanics. Review of previous literature and observation of test results show that hardening is highly dependent on confining pressures and the plasticity already experienced, which modify joint parameters by mutual interaction. This paper provides an insight into the published test data that reflects the dependencies of the in situ deformation modulus on incremental joint parameters and the isotropic pressure ratio. There exists an empirical relation between modulus ratio and modified joint factor derived from number of joints, roughness, joint inclination, and gouge parameters. The author has interpreted the modulus ratio of jointed rock based on the modified joint factor. The author applied a hardening parameter obtained from the initial condition of stresses and that of the joint on the modified joint factor to get a modulus ratio. Using a correlation of the modified joint factor and the rock quality designation (RQD), the model successfully shows that operating hardening parameter on RQD envelops the published data of modulus ratio versus RQD. The main aim of this paper is to show that the present model is valid for in situ deformation of the strain-hardening rock mass in structural foundation, mines, and excavation design. (C) 2013 American Society of Civil Engineers.