Research On Physical And Mechanical Properties And Brittleness Indexe Of Granite Under High Temperature Water Cooling Condition

Since humans' society entered the 21st century,the rapid economic development brings people the possibility of pursuing a higher quality of life.At the same time,the rapid deterioration of the ecological environment has made people's desire for clean energy more prominent.As the dimension of underground energy extraction expands,so does the search for clean energy;however,there are still many problems in the process of marching into deep underground rock masses that need to be effectively solved.For example,the development and extraction process of hot dry rock clean energy,the storage and placement of nuclear waste may have a harmful impact on the rock mass due to the high temperature environment,or the rock mass explosion caused by improper development inside the mine,and the repeated fires in geotechnical engineering projects are all huge safety hazards in the energy extraction process.The key to solving the above problems lies in the urgent need to carry out experimental research on the mechanical properties and internal structure of rock mass after experiencing high temperatures,in order to explore the changes in its internal physical properties,and then explore the deep causes of the deterioration of rock mass performance.As a reservoir of geothermal energy,the influence of real environmental factors on its related mechanical properties is extremely important for such experimental research.The granites were treated with high temperature water cooling by mechanical laboratory's related performance testing instruments to analyze their strength characteristics,physical and mechanical properties.The following research results were obtained by selecting granite from zigong region of Sichuan Province and treating it with high temperature water cooling:1.The mass loss rate of rock samples,the change of color of samples,the change of sonic velocity and porosity are studied.(1)The change of the surface color of granite is mainly gray-brown-off-white-light white-light red,and as the temperature increases,tiny cracks gradually occur on the surface of the specimen.(2)The loss rate,volume expansion rate,density change rate,porosity and sonic wave velocity value of granite mass continue to decrease with the increase of temperature,and there are obvious amplitude changes in the curve around 300?-400?.2.Uniaxial compression experiments and Brazilian splitting experiments were carried out on granite under different high temperature water cooling conditions.The test results showed that:?the peak strain of granite tends to increase with the temperature increase curve,and the compressive strength tends to decrease with the temperature increase.?The fractured form of granite changes from sudden rupture to steady-state rupture,reflecting the gradual transformation of granite from brittle delamination to ductile destruction.?The curves of modulus of elasticity and Poisson's ratio versus temperature show a gradual decrease with increasing temperature,and the curves of the two have been fitted,and the empirical formula of elastic modulus after thermal impact is obtained.?By obtaining the volume strain inflection point to determine the rock damage stress,the long-term strength curve of granite is obtained,and the observation curve finds that 400 ? is the threshold point of granite strength decay acceleration,and combined with the above conclusions,the threshold temperature of 300?-400 ? is determined as the strength change of granite.?The tensile strength of granite was inversely proportional to the increase of temperature by Brazilian cleavage method,and the tensile strength-temperature curve decreased linearly.?Based on the BP neural network model,the compressive strength and tensile strength of samples were trained and predicted,with the maximum error of 5.1%and the minimum error of 1.3%.The error was basically within the controllable range,which proved the rationality of the BP neural network model for strength prediction to a certain extent.3.Establish brittleness indicators based on cracking stress and damage stress.Based on the new brittleness index,the brittleness degree of high temperature watercooled granite was analyzed.The experimental results show that the brittleness index accords with the variation law of granite brittleness,it is proved that the failure mode of granite changes from brittleness to ductility with the increase of heating temperature.4.?ANSYS Workbench was used to simulate the stress field of the internal temperature field of granite after high temperature water cooling.It was found that under the premise of a certain temperature of cooling medium,the higher the temperature,the greater the change of temperature gradient,the greater the maximum cooling rate,the greater the thermal stress generated,and the greater the deterioration degree of granite?The temperature change of the surface of the granite is measured,and three characteristic stages of temperature change are obtained: the first stage: the rapid cooling stage;the second stage: the slow cooling stage;the third stage:temperature stable change stage;The temperature change of granite surface was measured,and three characteristic stages of temperature change were obtained: rapid cooling stage,slow cooling rate,stable temperature change stage;The measured data of surface temperature are recorded and compared with the simulated results.The temperature variation law of the two is consistent,which proves the rationality of the parameter selection.