Study On Cumulative Damage Characteristics Of Red Sandstone Under Dry And Wet Cycles

Under the influence of humidity factors,the red sandstone's physical and mechanical properties are significantly degraded,often causing various engineering disaster projects.In this paper,red sandstone is taken as the research object,and its cumulative damage characteristics under the action of dry-wet cycle is studied.The research results have important theoretical and practical significance for the long-term stability evaluation and geological disaster prevention of rock mass engineering in red sandstone area..The main research contents and conclusions of this paper are as follows:(1)The basic physical properties of red sandstone were studied.Basic physical tests and SEM,EDS and XRD tests were carried out to obtain the basic physical parameters,element content and mineral composition of red sandstone.The main elements of red sandstone contain O,Mg,Al,Si,K,Ca,Fe and mineral components:quartz,calcite,feldspar,mica,kaolinite,chlorite,illite,nontronite,Mongolian De-sparing,etc.;and the calculation and analysis of the water absorption rate of red sandstone shows that the water absorption of red sandstone increases with the increase of the number of cycles,but the incremental change of water absorption of red sandstone is weakened.(2)The strength characteristics of red sandstone under the number of dry and wet cycles were studied.Uniaxial compression test,split test,triaxial compression test,uniaxial compression test were carried out to obtain the relationship between stress and strain of red sandstone under different dry and wet cycles.The deformation characteristics,strength characteristics and failure characteristics of uniaxial compression test were carried out.The analysis shows that the peak strain increases with the increase of the dry-wet cycle,but the law of its change is not obvious.It can be seen that the red sandstone has a trend from brittle to plastic transition with the increase of the number of dry-wet cycles.The splitting test shows that the tensile strength has an exponential relationship with the number of dry and wet cycles.The triaxial compression test shows that when the rock is in the same dry-wet cycle state,the peak strength of the red sandstone sample increases with the confining pressure,and the corresponding strain also increases.When the rock is under the same confining pressure,the red The peak strength of the sandstone sample decreases with the increase of the number of dry and wet cycles.The higher the confining pressure,the smaller the peak stress increase.The analysis of the failure mode of the red sandstone shows that the red sandstone has increased with the increase of the numberof dry and wet cycles.The development trend from brittleness to plasticity is consistent with the results of uniaxial compression tests.(3)The damage characteristics of mechanical parameters of red sandstone under the action of dry-wet cycle are studied.The parameters such as total deterioration degree,stage deterioration degree and average deterioration degree in the stage are introduced to analyze the change of mechanical parameters with the number of cycles,and the logarithm function of the cycle number and the red sandstone mechanical parameters is fitted into a logarithmic function,and normalized.The order of deterioration damage from large to small is: tensile strength > uniaxial compressive strength > elastic modulus > internal friction angle > cohesive force;the damage coefficient is introduced,and the order from the largest to the smallest is:Tensile strength>uniaxial compressive strength>elastic modulus>internal friction angle>cohesion force;using Weibull statistical distribution probability density function,calculate damage variable,establish damage constitutive model,and based on the results of uniaxial compression test The verification analysis shows that the calculated theoretical curve can basically fit the stress-strain curve of the test piece.