Physical And Mechanical Properties Of High-Temperature Rocks After Different Cooling Treatments

With the development of underground engineering to deep strata,the study of rock mechanics is faced with more and more high temperature problems,and the exploration methods of geothermal,unconventional oil and gas resources in deep underground rocks are also discussed.In this paper,the physical and mechanical properties of high-temperature rocks under cold impact were studied by combining laboratory tests and numerical simulation.Marble and red sandstone samples were selected,and post-high temperature cold impact and uniaxial compression tests were conducted respectively.After that,the finite element numerical simulation software was used to simulate the tested engineering,and the changes of temperature field and stress field in the process of cold impact of high temperature rock were obtained,which further verified and supplemented the test conclusion.The test data and numerical calculation results were analyzed and the following conclusions were obtained:(1)Under the effect of cold impact after high temperature,the longitudinal wave velocity decreased significantly in the Dali rock test.However,the ultrasonic characteristics of red sandstone before and after cold impact were quite different from those of the Dali rock,and the wave velocity decreased little after cold impact.In general,the cold impact of liquid nitrogen caused the most damage to the two kinds of rocks.(2)Use the fluid such as water,liquid nitrogen cooling uniaxial compression after impact damage is more serious,many appear the phenomenon of powder and falling,and deeper through crack depth,crack width is bigger,water,liquid nitrogen for marble cold shock effect is good,and liquid nitrogen cold shock of marble effect is best,through the way of water impact damage mechanics characteristic of red sandstone.(3)There is also a significant difference between the stress-strain curves of marble and red sandstone.The axial strain corresponding to the peak stress of the curve of red sandstone is relatively large,and the strain is roughly 1.5~2 times of that of marble.(4)Based on the elastic modulus of rock of the definition of thermal damage factors and damage factor is similar to the overall trend of the definition of vertical wave velocity,but there is also a certain degree of difference,is mainly due to the determination of vertical wave velocity when ignoring the temperature effect on the rock density,the influence of poisson's ratio,etc,so the damage factor defined based on the elastic modulus of rock properties research accuracy is higher.(5)Comparing air natural cooling,water cooling impact and liquid nitrogen cold impact on the temperature field and stress field of high-temperature marble,it can be found that liquid nitrogen has the best effect on cold impact of marble,which is consistent with the conclusion of the experiment.