Physical And Mechanical Characteristics Of Water-Cooled High Temperature Granite And The Micro Damage Mechanism

The increasing demand for energy from economic and social development has attracted more and more attention in the development of dry hot rock geothermal energy.During drilling,the heat exchange between low temperature mud liquid and deep high temperature surrounding rock or low temperature water injection with dry hot rock will occur.Therefore,understanding the change law of physical and mechanical characteristics of high temperature rock after water cooling is the basis of solving deep rock engineering problems related to temperature.With the help of YAG-3000KN electro-hydraulic servo pressure testing machine,high temperature electric kiln,X ray diffraction analyzer,rock acoustic wave tester and electron microscope,the physical and mechanical characteristics and fracture damage mechanism of high temperature granite after water cooling are systematically analyzed in this paper.The main work and research results are as follows:The stress-strain curves of granite tests at normal temperature,200,400,600,800℃ after high temperature are measured systematically.The variation of elastic modulus,peak strain,peak strength and Poisson’s ratio with temperature are analyzed.Based on the X ray diffraction analysis and microscopic observation tests of granite specimens,the variation characteristics of rock-like mineral composition and the crack propagation of micro fracture surface under two cooling modes after high temperature are given.The results show that the high temperature action does not change the mineral composition,and the penetration and connection of a large number of transgranular cracks in rock samples are the important reasons for the deterioration of macroscopic phy sical and mechanical properties.The creep characteristics of granite after heating each temperature grade are obtained by graded loading creep test.The creep characteristics of granite after water cooling at high temperature are temperature and stress threshold.When heating temperature is 600,800℃ the creep phenomenon of granite specimen is obvious.After 1,2 and 3 cycles of cyclic heat-water cooling tests were carried out on granite specimens after high temperature,the variation of mass,volume,peak strength and peak strain with temperature and heating times after cyclic heating-water cooling were analyzed,and it was concluded that the increase of heating temperature and cycle times had great influence on the compaction stage and yield failure stage of rock samples.After 400℃ 2 cycles of heating,the brittleness characteristic was weakened and the stress-strain curve appeared yield platform.