Damage Mechanism Of Precast Fissure Granite Under High Temperature-water Cooling Impact

Based on the research background of major underground engineering projects such as the development and utilization of geothermal energy resources,the reconstruction of underground rock engineering after fire,and the deep mining of mine rock mass,this paper takes the typical granite through 1-10 cycles of heating(150℃-450℃)in the early stage to prepare fractured granite with different degrees of development.The apparent structure,density,p-wave velocity,porosity,permeability and other parameters of the granite were analyzed.The main conclusions are as follows:(1)The mass,volume,density and p-wave velocity of granite are linear with temperature,while the permeability is exponential with temperature;(2)Microscopically,when the granite underwent a thermal cycle at 150℃,some internal pores were closed.With the rise of temperature and the increase of cycle times,these cracks become wider and densified.The more the cracks and macules in the granite appearance structure,the greater the structural damage and mineral composition changes.At the later stage of the experiment,four kinds of granite with different degrees of thermal fracture obtained from the previous experiment were selected as test objects,and the high-temperature water-cooled impact test was carried out in the range of 650℃.The physical and mechanical characteristics such as apparent structure,longitudinal wave velocity,porosity,permeability,compressive strength,peak strain and post-peak strain of granite with different initial degrees of hot fissure under high temperature water cooling impact are analyzed.The results of the late test are as follows:(1)The appearance color of granite is greatly affected by heating temperature,while the appearance color is less affected by cooling method and initial fissure degree.The macroscopic thermal fracture process of granite first generates transverse cracks from the cylindrical end of the granite rock mass,and there are white stripes at the end of the cracks.With the enhancement of thermal stimulation,the white stripes gradually extend in the direction until they connect with each other and penetrate the entire granite mass,resulting in the granite slope splitting.(2)With the increase of temperature,the longitudinal wave velocity of each fracture group decreases,the porosity increases rapidly,the permeability first slows down and then rapidly increases exponentially,the strain resistance weakens,and the mechanical properties decrease.When the temperature reaches 550℃ or more,the curves suddenly change,and the granite of each fracture group presents different plastic characteristics.(3)Under the same temperature conditions,the effects of high-temperature water-cooling stimulation on the P-wave velocity,porosity,permeability and mechanical properties of granite are related to the degree of initial cracks.The larger the initial cracks,the more serious the final degradation and the more obvious the plastic characteristics.(4)There is a strong correlation between the P-wave velocity,permeability,mechanical properties and porosity of granite,and the P-wave velocity presents a concave inverse function relationship with the increase of porosity.With the increase of the porosity,the permeability of granite shows an exponential trend of slow growth at first and then rapid growth.The relationship between compressive strength and porosity is concave and inversely proportional.The fitting method of least square method shows a cubic function relationship between the peak strain and porosity of granite.