Analysis Of Strength Degradation Characteristics Of Unsaturated Soil Under Dry And Wet Cycle Conditions

In this paper,the characteristics of unsaturated soil strength degradation under dry and wet cycling conditions are analyzed.The unsaturated soil was studied,the mechanical characteristics and degradation laws of unsaturated soils under the action of dry and wet cycles are analyzed and studied.According to different initial physical conditions of unsaturated soil,tests of mechanical properties of unsaturated soils under dry-wet cycle conditions and tests of mechanical properties of unsaturated soils with or without load,obtain the degradation law of unsaturated soil and the cause of the often shallow slump of the slope.Based on the strength parameter degradation law obtained from the test,the stability analysis of the strength-degraded slope in the dry-wet cycle is performed to analyze the influence of the degradation caused by the dry-wet cycle on the stability of the unsaturated soil slope.The main research contents are as follows:(1)The basic physical properties of the soil and the particle gradation curve are obtained through laboratory natural moisture content tests,density tests,liquid-plastic tests,and particle analysis tests,which provide basic data for subsequent experimental study of the mechanical properties of unsaturated soils under dry and wet cycling conditions.(2)Through triaxial tests,the effects of different initial dry densities,different initial moisture contents,and dry-wet cycle amplitudes on the unsaturated soil’s dry-wet cycle process were comprehensively considered.The obtained stress-strain curves,shear strength,and strength parameters were analyzed the study.It is concluded that the degradation of soil strength caused by repeated dry and wet cycles is related to the initial dry density of the soil and the initial moisture content of the soil.The dry-wet cycle process has no significant effect on the form of the stress-strain curve.It only has a deteriorating effect on the shear strength.The shear strength decreases with the increase of the number of dry-wet cycles.Increasing the shear strength showed an increasing trend;the initial moisture content had less effect on the soil samples after undergoing the wet-dry cycle.The effect of dry-wet cycle on cohesion was significantly greater than the effect of internal friction angle.The internal friction angle and cohesive force decreased with the increase of the number of dry-wet cycles under dry-wet cycle conditions.Under the same number of dry-wet cycles,the internal friction angle and cohesive force increase with the increase of different initial dry densities,they decrease with the increase of different initial moisture contents.(3)In the dry and wet cycle,the slope is mostly shallow.In order to investigate the cause of the often shallow layer slump in unsaturated soil slope,a direct shear test was performed.The shear stress-shear displacement curve,shear strength degradation curve,Analysis of the total degradation of the shear strength parameters and the attenuation rate of the shear strength and the growth rate of the cohesion under the load.It is concluded that the shear strength shows a slowly decreasing trend.With the increase of the number of wet and dry cycles,the cohesive force gradually decreases and gradually decreases to a stable value,which has little effect on the internal friction angle.The dry-wet cycling process significantly degrades the soil samples without overlying load than soil samples with overlying load.(4)Using the degradation law of the shear strength parameters obtained in the test,the process of dry and wet cycles is simulated by PLAXIS to obtain the corresponding values of the horizontal displacement and the safety factor.The monitored cumulative displacement and rainfall data are compared to further analyze the dry and wet cycles of the action on slope stability.It is concluded that after the soil of the slope undergoes the dry-wet cycle,the stability of the slope is reduced,which can easily lead to the instability and failure of the slope and produce a landslide.The dry-wet cycle effect of the soil on the slope has a negligible effect on the stability of the slope and is one of the important factors causing the landslide.