Study On Static And Dynamic Properties And Damage Constitutive Model Of Granite Under Water-thermal Coupling

Our country has many mountain ranges,the terrain is undulating,the plate movement is active,the course and hydrogeological conditions are complex,especially in the Sichuan-Tibet area,geothermal resources are abundant,when the free water in the environment infiltrates underground,more geothermal hot springs are formed.In tunnel excavation,geothermal energy mining,and mechanical mining,the granite located near the working face is often damaged by mechanical impact under long-term hydrothermal action,which in turn affects the stability of the surrounding rock.Therefore,it is of great academic value and engineering significance to study the static properties,failure mode and damage process of granite under the interaction of water and heat.This paper takes granite in Sichuan-Tibet as the research object,and clarifies the macromesomechanical characteristics of granite after hydro-thermal damage and its controlling factors by carrying out inductively coupled plasma-mass spectrometry(ICP-MS)test,static and dynamic compression mechanics test,nuclear magnetic resonance(NMR)test and dynamic splitting test.The study exposed how water immersion temperature,immersion time,impact rate,and other factors affect the mechanical properties of the specimen,including peak stress,deformation performance,elastic modulus,and crushing mode,as well as their underlying mechanism.The main research results achieved are as follows:(1)Through microscopic tests on granite specimens with different immersion temperatures and different immersion times,it is found that the deeper the water-thermal action,the more gaps caused by dissolution at the corners of the granite;The water-rock reaction will stabilize around 4 months,when the number of internal pores of granite changes little.The immersion temperature can change the threshold of the water-rock reaction and accelerate the process of the water-rock reaction,the higher the immersion temperature,the more new pores are added inside the granite.(2)Through static and dynamic macroscopic mechanical tests,it is found that with the increase of hydro-thermal damage and the increase of impact rate,the fragmentation of granite specimens changes from large to small,the integrity of the main part becomes lower,and the powdery rock chips of the sample increase;The dynamic tensile strength,dynamic compressive strength and elastic modulus of granite decreased with the increase of water-thermal damage,and the change of water immersion temperature was the main reason for the decline of the above mechanical properties.The peak stress of granite increases with the increase of impact rate,showing obvious strain rate effect.(3)Compared with the static and dynamic compression mechanics tests,it is found that free water in granite pores promotes crack propagation under static loading conditions,and free water in granite pores inhibits crack propagation under dynamic loading conditions.Comparing the dynamic compression and tensile mechanics tests,it is found that the tensile strength and compressive strength of granite are similar to the law of compressive strength decline,and the amplitude is slightly different,indicating that the tensile performance is more sensitive to hydrothermal damage than the compressive performance.(4)Based on the dynamic compression mechanics test data,the empirical equations of elastic modulus variation with immersion temperature and immersion time were established.The strain equivalence principle was used to construct a damage intrinsic model of granite considering the immersion temperature and immersion time to explore the water-thermal damage process of granite,and the curve was compared with the test curve and found to be a good fit.