Study Of The Mechanical Properties Of Sandstone And Mudstone And Their Interfaces Under Drying-wetting Cycle

Interbedded rock masses are widely distributed in the southwestern part of the country.The temperature is higher and the precipitation is more in summer in this area.The resulting drying-wetting cycle will intensify the weathering degree of rock mass.It will lead to the deterioration of the mechanical properties of the rock mass,and eventually lead to the deterioration of the stability of the rock mass.In this paper,sandstone mudstone interbedded rock mass is taken as the research object.Uniaxial compression test and triaxial compression test are used to study the standard test pieces of sandstone,mudstone and interbedding of sandstone and mudstone in natural state and after drying-wetting cycle.Through PFC numerical simulation software,the uniaxial compression test and triaxial compression test of sandstone mudstone interbedded rock mass are carried out.Furthermore,the influence of the change of the thickness,dip angle and the mechanical properties at the interface of interbedded rock mass on the mechanical properties of rock mass is explored.The main achievements are as follows:(1)It is found from uniaxial test that the compressive strength of natural interlayered specimens decreases with the increase of inclination angle of specimens.It is found that the greater the confining pressure is,the greater the compressive strength of the interlayers is by the three axis test.As the dip angle of interbedding becomes steeper,the internal friction angle tends to increase slightly.The change rule of cohesion is not obvious.The compressive strength,modulus of elasticity,Poisson's ratio and other parameters of the specimen are significantly lower than those of the natural state after the drying-wetting cycle.Shear failure is the main mode of uniaxial compression failure of natural and drying-wetting cyclic interlayered specimens.The interlayered specimens show more obvious tensile splitting failure characteristics after drying-wetting cycle.In practical engineering,the slope of foundation pit should be excavated in different levels and protected with three prevention tarpaulins.Drainage measures shall be taken to prevent rainwater from accumulating,evaporating or losing in the rock mass,which will aggravate the drying-wetting cycle of the rock mass.(2)The results of PFC^3Dnumerical simulation of uniaxial and triaxial compression of sandstone mudstone interbedded rock mass show that the number of shear failure in rock mass increases with the increase of axial strain in natural state and drying-wetting cycle,accompanied by a small amount of tensile failure.When the failure critical state is reached,a macroscopic through fracture surface dominated by shear failure is formed.Under the same axial strain condition,the number of shear failure and tension failure increases obviously after the drying-wetting cycle.The peak strength of rock mass is obviously lower than that of natural state.Although shear failure is the main failure mode of rock mass in both States,the number of tensile failure increases significantly in the process of rock mass failure due to drying-wetting cycle.Therefore,the tensile failure characteristics of rock mass after the drying-wetting cycle are more obvious.(3)The thickness ratio has little influence on the elastic modulus and compressive strength of interbedded rock mass.However,the strength of rock mass increases with the increase of density of shale distribution.And it has a positive correlation with the micro mechanical strength of interbedded rock.The effect of drying-wetting cycle on the correlation is significant.Especially when the dip angle of rock is 60°?75°,the cracking degree of rock mass is more affected by the micro mechanical strength of rock layer.The failure mode is dominated by the shear failure of rock layer.