Analysis of excavation stability in hard rock tunnel by brittle elastoplasticity damage FEM

摘要

Loading and unloading conditions generally coexist in tunneling. Due to primary digenetic process and human activities, there are many structural surfaces like joints and crevices, which may drastically degrade the mechanical properties of the rockmass under the unloading conditions. Many engineering practices show that destabilization of surrounding rock in hard rock tunnels is not caused by loading conditions rather excavation causes release of earth stress and produces unloading actions, which then intensify rockmass deformation and increase connection rate of joints. As thus, the quality of rock-mass and mechanical properties deteriorate. Such rock mechanical properties under unloading conditions are essentially different from those under loading conditions. Therefore, the study on hard rock tunnels by mechanical models based on loading conditions goes against the unloading conditions of rockmass; hence, there must be discrepancy between the conclusion and actual engineering, consequently misguiding decision-making and inflicting great economic losses.