Study On Mechanical Properties Of Sandstone Under Freeze-thaw Conditions In Western Mining Area

At present,development of mineral resources has gradually developed to the western region in China.Due to the influence factors such as temperature,river,ice and snow in the cold regions of the west,the phenomenon of freeze-thaw damage in the rock mass of the mine has led to the occurrence of geotechnical engineering disasters.The prevention and management of freeze-thaw disasters has become an important research topic.Therefore,an in-depth understanding of the mechanism and evolution of rock freezing and thawing damage is of great significance to ensure the safe reclamation of mineral resources in the cold regions of the west.Based on the needs of the mining project in the cold area of western China,in this paper,sandstone samples were collected from the slope open-pit mine in western China to systematically investigate the mechanical properties of sandstone under different F-T and dyna-static loading conditions,such as compressive strength,elastic modulus,Poisson's ratio etc.,combing with scanning electron microscopy(SEM)test to analyze and study the damage characteristics of sandstone damage caused by freeze-thaw in the macroscopic and mesoscopic aspects.The energy of sandstone damage under different freezing and thawing Dissipative features for systematic analysis.The main research contents are as follows:(1)The static mechanical tests were carried out on sandstones under different freeze-thaw cycles.The stress-strain curves of sandstones under different freeze-thaw cycles were obtained.The effects of freeze-thaw cycles on the static mechanical properties of sandstones were studied,and the sandstone compression under static loads was determined.The variation of compressive strength,tensile strength,peak strain,elastic modulus and Poisson's ratio with freeze-thaw cycles were analyzed.(2)Dynamic mechanical tests were carried out on sandstones with different freezethaw cycles using the split Hopkinson pressure bar(SHPB)test system.The two-wave method was used to obtain the stress-strain curves of sandstones with different strain rates and different freeze-thaw cycles.The effect of rate and freeze-thaw cycle on dynamic mechanical properties were studied,and the variation of dynamic force compressive strength,dynamic tensile strength,dynamic elastic modulus with strain rate and number of freeze-thaw cycles were analyzed.(3)The macroscopic failure characteristics of sandstone under static load and dynamic load are studied systematically.Based on SEM,the mesomorphology of sandstone under different freeze-thaw cycles was obtained.The fracture mode and frost of sandstone are analyzed.The evolution law of the melting cycle;establish the relationship between the microscopic fracture and the macroscopic failure characteristics of the sandstone under different freezing and thawing cycles.(4)The damage constitutive relation of sandstone under the coupling of freezethaw cycle and static loading is established.The experimental data are compared and verified to provide a method for predicting and analyzing the mechanical properties of sandstone after freezing and thawing.The dynamic and destructive characteristics of freeze-thaw were studied by the principle of energy dissipation,and the relationship between energy dissipation of sandstone under different strain rates and different freeze-thaw cycles was analyzed.The research conclusions can provide a theoretical basis for the safety of mines and the prevention and control of freeze-thaw disasters in the cold regions of the western region.