Research On Damage Deterioration And Creep Characteristics Of Red Sandstone After Thermal Shock

Since the 21 st century,people’s demand for underground space resources continues to grow,and various rock engineering activities are being carried out in full swing,but people also encounter some problems in the process of entering the underground.In various projects,including geothermal resources development,underground oil and gas storage,reconstruction after rock engineering fire,nuclear waste disposal warehouse,etc.,engineering rock often meets the situation of rapid heating or cooling,that is,rock thermal shock phenomenon.Therefore,this paper combines laboratory tests and simulation,takes red sandstone as the research object,explores the damage and deterioration mechanism and creep characteristics of physical and mechanical properties of red sandstone after thermal shock,and simulates the changes of temperature field,stress field and crack propagation of red sandstone through numerical simulation software.Specific conclusions are as follows:(1)The basic physical parameters of red sandstone after thermal shock at different temperatures were measured,and the effects of thermal shock on sandstone mass,volume,density,p-wave velocity and porosity were studied.The results show that the mass loss rate,density reduction rate and porosity have exponential positive correlation trend with temperature,the volume expansion rate has quadratic positive correlation trend with temperature,and the P-wave velocity has quadratic negative correlation trend with temperature.All mechanical parameters deteriorate obviously between 500℃and 600℃.(2)Uniaxial compression tests and Brazil splitting tests were carried out on red sandstone specimens that experienced thermal shock damage at different temperatures(200℃-800℃).The results showed that the peak strength decreased with the increase of temperature as a quadratic function,and the peak strain increased with the increase of temperature as a quadratic function.The elastic modulus decreases exponentially and the deformation modulus decreases linearly with increasing temperature.The evolution process of the macroscopic failure mode of the thermal impact red sandstone is "splitting","inclined shear failure",and "shear-tensile coupling failure".At the mesodamage Angle,the thermal impact will produce cracks that cut off the mineral crystals,making the mineral particles present the coupling failure mode of intergranular and transgranular fracture.The load-displacement curve of Brazil splitting has a similar trend to the peak stress-strain curve,but the tensile strength is much smaller than the uniaxial compressive strength,and it decreases as a quadratic function with the increase of temperature.Based on the analysis of the thermal damage factors described by the change of elastic modulus and the change of longitudinal wave velocity,and Weibull strength distribution function,the damage constitutive model of the red sandstone damaged by thermal shock is established.(3)The uniaxial creep test is carried out on the red sandstone after thermal shock,and the influence of thermal shock damage on the creep characteristics of sandstone is explored by analyzing the creep deformation,steady creep rate,long-term strength,creep equivalence,etc.The results show that the creep deformation increases linearly with the increase of stress grade at the same temperature,and exponentially with the increase of temperature at the same stress grade.The creep failure strength decreases exponentially with increasing temperature,while the creep failure strain decreases quadratic function.Under the same stress grade,the higher the temperature is,the higher the steady-state creep rate is.With the increase of temperature,the long-term strength decreases approximately as a quadratic function.The possibility of stresstemperature creep equivalence of thermal shock red sandstone is investigated by comparing the creep curves of low stress with those of low damage(high temperature).(4)ANSYS Workbench software and ABAQUS software were used to simulate and analyze the temperature field,stress field and uniaxial compression test process of thermal shock red sandstone.The results show that the higher the temperature,the higher the cooling rate of the red sandstone during thermal shock,the greater the thermal shock stress of the outer surface of the model,and the stress concentration phenomenon appears in the upper and lower end and the middle part of the model.At400℃,the uniaxial failure mode of the red sandstone model is shear brittleness failure,and at 800℃,the failure mode of the red sandstone model is dilatation plastic failure.The simulation results are consistent with the actual situation and have high accuracy.