Mechanical Test Of Hard Brittle Rock And Its Strength Evolution Characteristics

Rock material is a kind of complex engineering medium which exists widely in mining engineering,water conservancy engineering,underground construction engineering and so on.In the deep high stress environment,the mechanical properties of rock materials,especially under complex stress paths,are very important for engineering safety.Therefore,it is necessary to conduct time-dependent hierarchical triaxial compression tests for marble.In view of this,this paper has carried on the conventional marble compression failure test and the constant confining pressure graded loading test to the deep buried diversion tunnel marble of Jinping secondary hydropower station.The main findings are as follows:(1)The compression failure test of deep-buried Jinping marble samples was carried out,and the failure characteristics of Jinping marble samples were obtained.(1)The experimental results show that the failure pattern of the marble varies obviously with the increase of confining pressure.Specifically,the failure pattern of the marble under the test is different.It can be seen that with the increase of confining pressure,the failure degree of marble decreases,which indicates that confining pressure improves the stress state of marble and inhibits the development of failure.(2)At the conventional triaxial compression condition,the strength reaches the peak,and the brittle failure occurs with the increase of strain under the condition of low confining pressure,while obvious ductile failure occurs when the confining pressure strength reaches 15 MPa.(3)The failure of rock samples in conventional triaxial compression tests is achieved by the increase ? internal friction angle and the c of cohesion.(2)The basic mechanical parameters,such as deformation and strength of rock samples,and the regularity of time-effect of their failure characteristics are obtained by studying the constant confining pressure and graded loading of marble samples.(1)Among them,because the loading time in the graded loading triaxial compression test is significantly higher than that in the conventional triaxial compression test,the failure morphology of the rock samples is obviously different from that in the conventional triaxial compression test.(2)Compared with conventional triaxial compression tests,the peak stress decreases 13.52%,16.02%,12.56% when the confining pressure is 5 MPa?10MPa?15MPa.It can be seen that in the triaxial compression test of graded loading,the strength of rock is obviously lower than that of conventional compression test in the same confining pressure level.(3)Under different loading conditions,the strength parameters of rock materials are significantly reduced,in which the cohesive force and friction angle determined by the yield strength as the ?0.2 and the yield strength as 80%?f are in accordance with the law: the internal friction angle of the graded loading test is ?increasing compared with the conventional triaxial compression test,while the cohesive force is c decreasing,indicating that the graded loading test will lead to more severe damage inside the rock and deterioration of its mechanical properties.(4)There areobvious rules between rock strain and stress in the graded loading test,that is,with the increase of stress level,both axial strain and circumferential strain of rock show the trend of increasing step by step.The deformation of hard brittle rock mainly occurs in the failure stage.