Research On Unloading Failure Mechanism Of Rock Under High Stress And Its Application

The deformation and failure of rock mass is closely related to loading status and its supporting environment. loading and unloading can induced rock mass deformed and failure. The different stress paths cause rock mass in different deform and failure process. Foundation engineering is unloading as excavating, it is loading when structure is built. Slope engineering mainly is unloading. The tangent stress of underground engineering secondary stress filed is loading, the radial stress is unloading.Research on rock mass unloading failure mechanism has very important theoretical significance to unloading rock mass mechanical behavior and its failure mechanical mechanism, develop rock mass theory, study on geological disaster induced from mankind engineering activity. It has great economic benefit and highly practical values to rock mass engineering practices. In the past ten years, with the rock mechanics development and the need of engineering structure, research on rock unloading test had developed in some degree. Some achievement had obtained in unloading rock deforming damage character, the relating of strength and stress paths, which provide basis to research on rock mass deforming damage property under unloading status.Based on plenty of tests, the marble from JinPing Hydropower Station is studied. The achievements are as follows:(1) Uniaxial test, triaxial test, pro-peak unloading confining test and post-peak unloading test are done in the MTS machine and got that marble has different strength and deformation character in different test ways. The main manifestations is that samples are all brittle failure in pro-peak and post-peak unloading confining test. Compare to conventional triaxial test, unloading confining more induced rock failure and the failure degree is more strongly. The brittle character in pro-peak unloading confining test is more strongly than in post-peak unloading confining test. These provide necessary test data to building marble unloading yielding criterion and elastic-plastic constitutive model. (2) Based on unloading confining tests, provided power function Mohr strength criterion and compared to hyperbolic and parabolic Mohr strength criterion. The failure curve of power function Mohr strength criterion inπplane is done.(3)From porosity concept defined damage variable of material. Using power function Mohr strength criterion and associated flow rule built elastic-plastic damage constitutive model of marble unloading failure. FORTRAN was used to program user subroutine to connect with ABAQUS.(4) Based on the theoretical analysis, the constitutive model is connected to the commercial finite element analysis software ABAQUS by user subroutines, and analyzed the rock mass's stability of Jinping hydropower station's diversion tunnel. And compared to the result of mohr-coulomb strength criterion. It shows that the proposed constitutive model in this study is scientific and reasonable.