Experimental Study On Mechanical Properties Of Granite After Heat Treatment Under Unloading Conditions

In this thesis,the heat-treated granite is subjected to water cooling conditions,and the physical properties and mechanical properties after heat treatment are studied by means of physical properties tests and mechanical properties tests.The granite unloading pressure after cooling at high temperature is studied.Mechanical properties under conditions.The tests involved in this paper include physical property tests and mechanical property tests.Physical property tests include density and porosity tests,SEM electron microscopy scans,and X-ray diffraction experiments.Mechanical properties tests include conventional triaxial tests and unloading confining pressure tests.Through the physical properties test,the granite density,porosity,internal structure change of the rock samples after heat treatment and granite internal composition can be obtained.Through the triaxial normal test and unloading confining pressure test,the mechanical parameters and strength parameters are obtained,which provides a more real and reliable theoretical basis for engineering examples.The following conclusions can be drawn from this study:(1)With the increase of heat treatment temperature,the porosity of granite samples continuously increases,because the internal cracks of granite gradually increase due to temperature.Through X-ray diffraction experiments,the main mineral compositions and mass percentages were quartz(10.03%),potassium feldspar(24.51%),albite(35.45%),mica(28.77%),and chlorite.(1.16%)and calcite(0.12%).Its natural density is 2.63g/cm3 and its porosity is 0.0192.(2)There are two main reasons for the destruction of the ring under the circumstance of unloading confining pressure.One is that the temperature effect(thermal stress)causes cracks and damage to the granite,and the other is that the ring deformation of the granite is continuously increased due to the unloading of confining pressure damage.The unloading confining pressure process and the loading process are the opposite processes.With the continual reduction of confining pressure,the compressive strength of the granite under the changed state is continuously reduced.In addition,the hoop strain of granite is more and more small due to the pressure in this direction,the hoop strain is getting bigger and bigger,and the microfissures grow up and cross each other.(3)Calculating the confining pressure confining pressure increment ratio of the unloading confining pressure strain at different temperatures of the rock sample shows that the circumferential deformation is more sensitive to the unloading confining pressure than the axial deformation.At 900°C,the confining pressure increment ratio is the largest,followed by 400°C,and 25°C the minimum.It shows that the rock samples after the water cooling at 900°C are most sensitive to the unloading pressure.(4)With the constant unloading of confining pressure,the Poisson's ratio of granite is increasing.According to the Mohr-Coulomb criterion,the c and ? of the granite samples were determined.After 900 °C water cooling,the cohesion force reached the minimum,and the internal friction angle changed more slowly.