ESTIMATION OF HYDRAULIC PROPERTY OF JOINTED ROCK MASS CONSIDERING EXCAVATION-INDUCED CHANGE IN PERMEABILITY OF EACH JOINTS

摘要

Underground excavation can induce significant deformation of pre-existing joints in rock mass. Due to the sliding and opening of the joints, consequent changes in the flow characteristics of a jointed rock mass would be anticipated. In the present work, the finite element excavation analysis for a jointed rock mass and the finite element flow and transport analysis using the discrete joint network model are employed and combined so as to make it possible to evaluate excavation induced changes in flow properties of a jointed rock mass. A separate computational module connecting these two codes is incorporated to modify initially imposed transmissivities into the excavation induced ones considering the deformation of joints during an excavation. The effect of excavation on the flow properties is evaluated by including these excavation induced transmissivity changes of individual joints. The excavation induced transmissivities are calculated using the analytical approximation solution developed for flow through a single rock joint. The calculation of the excavation induced transmissivity involves the distributions of shear displacements and normal stresses around the excavation, and explicitly takes into account of the effect of surface geometric roughness. A test simulation for a deep underground repository is performed to demonstrate the typical results predicted in the proposed approach.