Study On Mechanical Characteristics Of Red Sandstone Under Freeze-thaw And Cyclic Loading

China’s permafrost area is about 2.06 million square kilometers,second only to Canada and Russia,and about 1.5 times the area of the permafrost region in the United States.Counting the seasonal frozen soil,the area of China’s permafrost area accounts for about 70%.With the construction of cold area projects,many problems will inevitably be encountered.For example,the rock and soil in the cold area face a series of problems such as freeze-thaw cycles,composite erosion,shrinkage,damage and damage,and mineral resources are not available during mining Avoid various dynamic load disturbances such as blasting,ore collapse,natural earthquakes and landslides.Therefore,it is particularly important to study the changes of damping parameters,dynamic elastic modulus,and dissipated energy of red sandstone under freeze-thaw and freezing conditions,providing a certain reference value for the long-term stability and seismic parameters of cold regions.Red sandstone was processed into a standard rock sample（Φ50mm×100mm）by laboratory core sampling,and its basic physical parameters were measured by saturation test.Cyclic loading and unloading tests were carried out on red sandstones under different cycles of freezing and freezing and thawing times.As the number of cycles of freezing and thawing and freezing and the dynamic stress coefficient increase,the dissipated energy of red sandstones gradually increases;as the number of cycles of freezing and thawing increases,the dynamic elastic modulus of red sandstones decreases.As the dynamic stress coefficient increases,the dynamic elastic modulus gradually increases;as the number of freeze-thaw times increases,the rate of decrease of freeze-thaw red sandstone is greater than the rate of decrease of frozen red sandstone,and the The difference is small when the number of times is 0.With the increase of the number of cycles of freezing and thawing,the damping ratio gradually increases,but the damping ratio does decrease gradually with the increase of the dynamic stress coefficient,and the red sandstone damping ratio under the freeze-thaw conditions follows a power function F（x）=ax^bdecreasing trend,the damping ratio of frozen red sandstone is slightly larger than that of frozen and thawed red sandstone under the same freezing times and dynamic stress coefficient.The damping coefficients of freeze-thaw and frozen red sandstone both increase with the number of cycles of freezing and thawing,and decrease with the increase of the dynamic stress coefficient.For frozen and freeze-thaw red sandstones,the change rates of the damping coefficient from 0 to 80 freezing conditions are:v_0.60>v_0.24>v_0.48>v_0.36,v_0.24>v_0.60>v_0.48>v_0.36,and the number of increase in damping coefficient of freezing and thawing conditions and the dynamic stress coefficient have a relationship of quadratic parabola of F（x）=Ax²+Bx+C.A comparative analysis of the damping coefficient of red sandstone under freezing and thawing and freezing finds that the damping coefficient of red sandstone under cyclic freezing is greater than the damping coefficient of red sandstone under cyclic freezing and thawing under the same freezing and thawing times and the same amplitude load.