Strain Energy Dissipation and Damage Evolution of Frozen Migmatite Under Triaxial Unloading

The aim of this paper is to study the effect of unloading, due to excavation, on the damage evolution and energy dissipation of frozen rock slopes. Triaxial unloading tests were conducted on frozen migmatite from the Dagushan Iron Mine using acoustic emission location technology. When the confining pressure was unloaded, the axial stress was held constant. The purpose of this experiment is to establish the relationship between macroscopic energy dissipation and microscopic damage. Damage is small in hydrostatic pressure stage but increases abruptly during the failure stage, and increase rate is about 10 times that of loading tests for frozen migmatite and 2 times that for room temperature. In the deformation acceleration stage, both the damage and dissipation energy increase suddenly and the damage increment increases before the dissipation energy, i.e., the accumulation of damage eventually manifests itself as macroscopic energy dissipation. The dissipation energy can be expressed by a superposition of two exponential damage functions. Moreover, the percentage of dissipation energy and damage, in failure stage, is more than 60% for unloading tests. However, for loading tests the percentage of damage in the failure stage is less than 25%, and most of the damage occurs in the unstable deformation stage.