Experimental Research On The Influence Of High Temperature On The Tensile Properties Of Granite

Geothermal resource extraction is currently a hot topic.Due to its cleanliness and wide spatial distribution,geothermal energy has become the third largest renewable energy after hydropower and biomass energy.In the deep and complex underground environment,the mining of dry and hot rocks mainly forms fractures by hydraulic fracturing,which is used by artificial water injection,and the whole process is in a closed cycle.Therefore,in this paper,the granite after heating treatment with different water temperatures(0?,25? and 80?)and cooling by stages treatment.Then the tensile strength of granite is tested by splitting.Finally,the fissure permeability test is carried out on the fissures produced by splitting.This article takes granite as the research object,starting with the basic physical and mechanical properties of the sample(dry density,saturation density,porosity,longitudinal wave velocity,thermal conductivity),and analyzes the effect of different cooling treatment methods on the physical properties of granite and the changes with temperature law.The tensile mechanics test was carried out by the rock-soil medium fully-coupled multifunctional test system,and the Brazilian split test was carried out on the samples treated by different cooling methods to obtain the evolution of temperature and tensile mechanical properties under different cooling methods law.At the same time,based on the fractured granite samples produced by the Brazilian split test,the laboratory hydraulic seepage system was used to subject the split granite samples to liquids under different confining pressure conditions(2MPa,10 MPa,20MPa,30 MPa,40MPa,50MPa)Permeation test to obtain the evolution law of the permeability of the fracture under the conditions of temperature and confining pressure.The main conclusions are as follows:(1)The density,longitudinal wave velocity and thermal conductivity of granite decrease with the increase of heat treatment temperature,and the porosity increases with the increase of heat treatment temperature.(2)Different quenching water temperatures have no obvious effect on the tensile mechanical properties of the samples.The tensile strength of the granite samples cooling by stages treatment is greater than the quenched samples;the mechanical properties of the samples processed in stages of cooling are more stable than the quenching.(3)The tensile strength and compressive strength of granite have different sensitivity to temperature.When the heat treatment temperature reaches 300°C,the tensile properties of granite begin to deteriorate,while the compressive properties only begin to decay when the heat treatment temperature reaches 500°C.The mechanism of tensile failure and compression failure is different.The main factors affecting the tensile strength of granite are the cohesion and fracture state of mineral particles,the compressive strength of granite depends on the strength of the granite skeleton,the size of the internal cracks,the strength of the mineral composition and the bonding force.(4)Confining pressure has a very strong inhibitory effect on the permeability of granite fissures.As the confining pressure is worth increasing,the permeability of the fissure gradually decreases,and eventually it will stabilize at an extreme value.The state of splitting fissures is the main factor affecting the permeability coefficient.