Experimental Study On Deformation And Failure Change Of Sandstone Under Freeze-Thaw Cycles

The weathering problem of the Yungang Grottoes has been a long-standing problem.The freeze-thaw cycle is an important factor in the weathering of the sandstone.Studying the deformation and failure law of the sandstone under condition of freeze-thaw cycles is of great significance to the freeze-thaw resistance of the Yungang Grottoes.On the basis of summarizing previous studies,this paper studies the freeze-thaw deformation and failure law of bedding sandstone with different moisture contents under condition of freeze-thaw cycles,and freeze-thaw experiments to bedding sandstone with different moisture contents was carried out.The specific research work is:The freeze-thaw cycle experiments were carried out to the bedding and intact sandstone under three water-containing conditions: saturated water,natural water and dry.The macroscopic physical and mechanical parameters of sandstone in each state were measured with the freeze-thaw cycle.As the time of freeze-thaw cycle increases,the longitudinal wave velocity,mass,compressive strength,tensile strength and elastic modulus decrease.Water and bedding weakened the freeze-thaw resistance of rock samples.The strain change process of six state rock samples was measured in real time during the freeze-thaw cycle.The results show that the deformation of water-bearing rock samples mainly includes the thermal expansion and contraction deformation caused by temperature effect and the frost deformation caused by water icing expansion.The thermal expansion and contraction deformation is affected by the non-uniformity of the particle composition and particle composition of the rock sample.Therefore,the bedding rock sample has larger thermal expansion and contraction deformation than the intact rock sample,and the higher moisture content,the greater frost heaving deformation.The microscopic appearance of the rock samples after different freeze-thaw cycles were observed.With the increase of freeze-thaw cycles,the cement at the microscopic scale appears loose and the density decreases,accompanied by the initiation and development of the fissure.The location of the fracture appearance mainly includes the cement-particle junction and the particle-particle junction.At the meso-scale,the saturated water bedding samples are prone to cracks,and the fracture direction is parallel to the bedding direction.As the freeze-thaw cycle increases,the width and number of fracture increase,and produce crack network.The mechanism of freez-thaw deformation and failure of sandstone in different states was discussed.The deformation and failure mechanism caused by heterogeneity and frost heaving were respectively discussed,and the relationship between fracture expansion rate andfreeze-thaw cycle was established.The results show that the existence of bedding results in a weak surface and a non-uniformity at the junction with the sandstone matrix,which is easy to be deformed and destroyed here.In addition,the presence of water seriously weakens the resistance of the sandstone to freeze-thaw.There are 59 figures,11 tables and 88 references.