Experimental Study On Granite's Shear Mechanical Properties In Different Stress Paths After High Temperature

During the storage of nuclear waste in storage depots and the exploitation of geothermal resources in deep dry hot rocks,as well as when underground geotechnical engineering structures are exposed to fire,the rock mass structures are under the action of high temperature and different stress paths,which have significant effects on the physical and mechanical properties of rocks.However,in-depth study on the changes of physical and mechanical properties of granite under different stress paths after high temperature has great scientific significance for practical engineering and can provide technical guidance for practical engineering.In this paper,Jieyang granite in Guangdong province has been taken as the research object,the influences of temperature,stress loading path and heat treatment method on the physical parameters,shear mechanical properties and failure modes of granite specimens are analyzed with the aid of various instruments.The specific conclusions are as follows:(1)With the increase of temperature,the shear mechanical properties of granite gradually deteriorate,and its shear characteristic value changes most obviously at 300??400?,which is the thermal damage temperature threshold region of granite.(2)With the increase of temperature,the internal friction angle of granite is different from that of common granite,which shows a continuous downward trend,but increases first and then decreases.This is due to the ?-? phase transformation of Quartz crystal grains after 300?,and the sudden volume expansion,which leads to the sudden increase of thermal damage of granite.Under the action of shear stress,the granite crystal grains may undergo damage,resulting in a downward trend of internal friction angle.(3)Through comparison of failure modes,the failure of specimens in normal normal direct shear test is mainly caused by shear failure caused by a through crack,while the specimens in tangential cyclic shear test are inferior to those in normal normal normal direct shear test in various mechanical properties due to accumulated local shear failure caused by cyclic loading in addition to shear failure caused by through crack.(4)Compared with the specimens after cooling in water,the shear characteristics of specimens after cooling in water before 300? are not much different,while after 300?,the shear characteristics of specimens after cooling in water are significantly lower than those after cooling in nature,and the mechanical properties of specimens are significantly deteriorated.Therefore,300? is the threshold value for the influence of mechanical properties of specimens after cooling in water at high temperature.