| The rock located in the deep underground is faced with complex geothermal environment and confining pressure environment,and the stability of surrounding rock of deep engineering facilities is directly related to the safety of the overall engineering facilities.Granite is characterized by wide horizontal and vertical distribution,high compressive strength and good compactness,and is often used as the thermal reservoir of geothermal resources or most of the wall rock components.In the process of deep engineering construction,the change of temperature field and stress field will make it difficult to predict the damage of granite,and then lose control of the overall fracture network of surrounding rock,laying a hidden danger for construction safety and long-term stable use of facilities.Therefore,the study of the mechanical properties and failure mechanism of granite under different temperatures and forces can provide a reference for evaluating the safety factor of surrounding rock in deep engineering,and has important theoretical value and engineering significance.This paper takes high temperature and high temperature cooled granite as the research object,carries out uniaxial compression and dynamic compression experiments under different processing temperatures,and studies the mechanical characteristics change and failure mechanism of granite after high temperature and high temperature cooling by using physical experiments,numerical simulation,theoretical analysis and other methods.The main research contents and conclusions are as follows:(1)Under uniaxial compression,the mechanical properties of the granite after high temperature and high temperature cooling are similar.Compared with the granite under high temperature,the peak strength and elastic modulus of the granite after high temperature cooling are lower and the elastic modulus is higher in the corresponding temperature group.The compressive strength and modulus of elasticity of the two decreased with the increase of temperature,with the largest decrease at 25 ℃～200 ℃;The peak strain increases with the increase of temperature,and increases greatly at 25 ℃～200 ℃ and 400 ℃～800 ℃.Therefore,it is found that the critical temperature of brittle transformation of granite is between 25 ℃ and 200 ℃.At573 ℃,the quartz particles,the main component of granite,will be modified,which will aggravate the thermal damage of granite.It can also be determined that there is a temperature threshold for the completion of granite plasticity between 400 ℃ and600 ℃.(2)Before 200 ℃,the failure mode of granite at high temperature and after high temperature cooling is the same,which is cleavage failure.With the increase of temperature,the failure mode of both approaches to conjugate shear failure,but the difference also begins to be obvious.The failure surface of granite at high temperature is gradually X-shaped,and the integrity of the main body and fragment of rock sample is high;After high temperature cooling,the failure surface of granite gradually assumes V-shape,and the main body of rock sample is relatively complete,but the fragmentation degree is relatively high.(3)Under dynamic compression conditions,the mechanical properties of granite at high temperature and after high temperature cooling are generally similar.The dynamic peak strength and dynamic modulus of elasticity decrease with the increase of temperature,while the dynamic peak strain increases with the increase of temperature.The three have temperature thresholds at 25 ℃～200 ℃ and 400 ℃～600 ℃;Impact velocity has certain influence on the mechanical properties of granite.In the same temperature group,the greater the impact velocity,the greater the dynamic peak strength and dynamic peak strain,and the smaller the elastic modulus.However,the impact of impact velocity on the three will decrease with the increase of temperature.At 400 ℃～600 ℃,this effect is far less than that of temperature.In addition,within 25 ℃～200 ℃,there is a velocity threshold of impact velocity at 10m/s～20 m/s. |
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