Experimental And Damage Constitutive Model Study On Triaxial Mechanical Properties Of Sandstone Under Brine Drying-wetting Cycle

Phenomena such as rainfall and evaporation in nature,periodic rise and fall of reservoir and groundwater levels are easy to cause instability of engineering structures such as mountain slopes and reservoir dams and induce geological hazards such as landslides and dam collapses.Essentially,the physical and mechanical behavior of the rock deteriorates after repeated drying-wetting cycle in the brine environment,which makes it more susceptible to destabilization and damage under the action of external forces.Based on it,this thesis used combination of laboratory tests and theoretical research to investigate the effects of brine environment and drying-wetting cycle on the physical and mechanical properties of sandstone,analyzed the physical parameters,strength and deformation characteristics of sandstone under the action of different times of drying-wetting cycle,and revealed its damage and rupture mechanism,in order to provide some reference and guidance for the stability control of engineering slopes and dams.The main research contents and conclusions are as follows:(1)The mass,volume and permeability tests of sandstones undergoing different times of drying-wetting cycle in brine environment were carried out to determine the change pattern of physical properties of the rocks under the effect of brine dryingwetting cycles.Five drying-wetting cycles is the threshold values for the changes in mass and permeability of the specimens,and the degradation effect of brine dryingwetting cycles on the physical properties of the rocks is significantly higher than that of water drying-wetting cycle.Based on scanning electron microscope observations,it is shown that the loss of intergranular clay mineral components inside the rock is the main cause of its damage.(2)The mechanical properties of dry sandstone and saturated sandstones undergoing the same times of drying-wetting cycle in brine and water environments were compared and analyzed,and the deterioration mechanism of rock mechanical properties caused by solution environment after drying-wetting cycle was discussed.Water dissolve the clay minerals in the rock,resulting in the deterioration of the mechanical properties of sandstone.The effects of brine on rocks include crystal filling gain and chemical dissolution deterioration.When brine crystals fill the internal pores of rocks,chemical dissolution also accelerate the loss of clay minerals,so that the deterioration of mechanical parameters of sandstone in brine environment is greater than that of samples in water environment.(3)The triaxial compression test of sandstone under different times of dryingwetting cycle in brine environment was carried out to further analyze the damage deterioration law of the rock by times of drying-wetting cycle in detail.With the increase of the times of drying-weting cycle,the rate of deterioration is low in the first10 drying-wetting cycles and increased significantly thereafter,and the overall rate of deterioration shows the trend of first decreasing and then increasing.The pores formed by the loss of clay minerals are filled with Na Cl crystals,which makes the deterioration rate of rocks lower in the early stage.Later the effect of Na Cl crystal filling is inferior to the damage caused by mass loss of clay minerals,which leads to higher deterioration rate of rock mechanical properties.(4)Based on the mechanical test results of sandstone under different times of drying-wetting cycle in brine environment,damage intrinsic model of sandstone considering the coupled damage of drying-wetting cycle of brine and load was established by combining fine damage theory and macroscopic statistical damage model.The model can better reflect the damage evolution of sandstone after the action of drying-wetting cycle of brine,and the trend of the theoretical curve is basically consistent with the laboratory test curve.This thesis includes 69 figures,15 tables and 113 references.