Characteristics of Brittle Failure and Stress Drop Under Triaxial Loading and Unloading
HUANG Da,HUANG Run-qiu and ZHANG Yong-xing
DOI:10.11835/j.issn.1674-4764.2011.02.002
Received July 16, 2010,Revised , Accepted , Available online July 01, 2015
Volume ,2011,Pages 1-6
- Abstract
The characteristics of deformation failure and stress brittle drop of granite under loading and unloading conditions are studied respectively based on two unloading stress path cases and conventional triaxial compression experiments. The experiments show that the primary deformation of rock is rebound or tension in the (main) unloading direction, but plastic deformation in the non or sub unloading direction is not significant. And the curves of stress strain after peak strength present obvious brittle. Whilst the primary deformation of rock under loading is axial pressure deformation, and plastic deformation increases with the raise of confining pressure. The fracture is characterized by strong tensile, and all tensile cracks are fully developed. Furthermore, when the rock samples are unloaded in two directions, and even normal to unloading direction, sub unloading annular tensile cracks are produced. The shear fractures is obvious comparatively when confining pressure becomes higher, and it develops following tensile cracks with more micro tension cracks formed in two sides along shear plane. But the fracture is characterized by shear under conventional triaxial compression with little tensile cracks; the coefficients of brittles stress drop of granite is increased with the growth of confining pressure under conventional triaxial compression and reduced under unloading. When the initial confining pressure is the same, the coefficients of brittles stress drop under unloading is less than that under loading. In SchemeⅡ, the coefficients of brittles stress drop reaches negative when initial confining pressure is up to 30 MPa, and the one （R）is RⅢ>RⅠ>RⅡ in three test cases.