Modeling time-dependent deformation behavior of jointed rock mass

Abstract

Long-term stability analysis and stand-up time prediction of underground excavations are important in engineering design and construction. In this thesis, a numerical study of the time-dependent deformation behavior of jointed rock mass is presented. Firstly, creep deformation behavior of intact rock is studied numerically using the grainbased modeling (GBM) approach based on the Distinct Element Method (DEM). A grainbased time-to-failure (GBM-TtoF) creep model for intact brittle rocks is proposed to simulate creep deformations in the first two creep stages and time-dependent failure at the tertiary creep stage. Parameters of the TtoF model are calibrated using experimental data of Lac du Bonnet (LdB) granite. Simulations of the time-dependent deformation of rock pillars using the GBM-TtoF model are conducted. The influence of pillar shape (width to height ratio) and loading ratio (stress / strength) on the time-dependent spalling on pillar walls is investigated. Secondly, creep deformation of rock joints is simulated by using the grain-based joint models that are established using the GBM-TtoF model. The influences of joint roughness and loading conditions (normal and shear stresses) on the long-term shear strength and creep sliding velocity of joints are investigated. A new creep model is proposed, which can be used to control the creep deformation behavior of flat joints in the DEM. The model is validated using experimental data of joints. Thirdly, a creep model for jointed rock masses, which can consider time-dependent deformations of both rock and joints, is proposed. Creep deformations of jointed rock masses are simulated using a few jointed rock mass models, i.e., a rock mass model with a single joint, a jointed pillar model and a high rock slope model. The creep deformation characteristics of the jointed rock mass models are analyzed. Finally, time-dependent deformation behaviors of tunnels excavated in jointed rock masses are simulated using the creep model for jointed rock masses. The weakening of face-effect due to creep deformation of the rock mass is modeled using the internal pressure reduction method and the convergence-confinement method. The stand-up time of unsupported tunnels is simulated considering the influence of rock mass quality and the unsupported roof span. The simulated result is validated using Bieniawski’s stand-up time chart. The models developed in this thesis provide novel numerical approaches to simulating creep deformations of rock, joints and jointed rock masses, and are important for improving the understanding of the time-dependent deformation behavior of jointed rock masses.