| Most areas in northern China are arid or semi-arid areas.With the gradual deterioration of the environment in recent years,plants in some areas continue to degenerate and the degree of desertification continues to worsen.Water retaining agent is an important means for controlling soil erosion,desertification,and many other issues.Mastering the influence rule and mechanism of water retaining agents on soil strength under different water content conditions,improving the theoretical system of the impact of water retaining agents on soil,providing a theoretical basis for the future use of water retaining agents in slope protection,and also helping to promote the application of water retaining agents in soil and water conservation,has significant theoretical significance and application value.In order to study the mechanism and stability of shallow landslides induced by rainfall,direct shear tests,interfacial shear tests,and slope model tests were used to study the slope with dual structure in the study area.In this paper,two sets of 14 slope model tests under 7working conditions were conducted for soil without and with water retaining agent,with water content of 4%,7%,10%,13%,16%,19%,and 22%,respectively.Further,the characteristics of landslide failure and the law of action of water retaining agent under this water content are obtained,and the changes in the sliding surface position,surface displacement,soil pressure,and slope stability of the shallow layer landslide of a binary structure slope under different water content conditions are analyzed,revealing the deformation and failure mechanism of the shallow layer landslide.The development of this slope model test provides a scientific basis for the mechanism of shallow surface landslides of binary structure slopes,and also provides a theoretical basis for the prevention and treatment of shallow surface landslides of binary structure slopes with water retaining agents.The main results achieved are as follows:(1)A set of soil rock dual structure slope test model is designed to fully reflect the sliding surface position change trend,slope displacement change trend,slope earth pressure change trend,and slope stability change trend of soil rock dual structure slope under the influence of water content through the test,revealing the instability mechanism of soil rock dual structure slope.(2)Based on the analysis of direct shear test data of soil without water retaining agent and soil with water retaining agent,the optimal content of water retaining agent is determined to be 0.3%.The influence of water content on the internal friction angle and cohesion of soil mixed with 0.3% water retaining agent was discussed.The functions of water content,cohesion,and internal friction angle are proposed,and the expression formulas for shear strength of soil samples mixed with 0.3% water retaining agent under different water contents are proposed.(3)An interfacial shear test was conducted on the soil rock interface between soil mass without water retaining agent and soil mass with water retaining agent in a binary structure slope,and the test data were analyzed.Under low normal stress conditions,with the increase of water content,the cohesion at the soil rock interface without water retaining agent first increases,then decreases,and finally tends to be gentle,reaching a peak value near the optimal water content of 13%;The effect of water content on the cohesion of soil rock interface with water retaining agent presents three stages: rapid rise stage,rapid decline stage,and slow decline stage,with the peak value of cohesion reaching around16% of water content.As the water content increases,the friction angle of the soil rock interface between the slope without water retaining agent and the slope with water retaining agent generally presents a rapid downward trend.(4)Compared with soil slopes without water retaining agent,adding water retaining agent can effectively reduce the volume of soil above the sliding surface,reduce the amount of landslides,and improve the stability of the slope under conditions of medium to high water content.At low water content,the addition of water retaining agent will increase the sliding area of the slope and reduce the stability of the slope.The soil pressure at the slope toe will gradually increase as the water content of the soil mass without water retaining agent increases;The previous tests of soil pressure at the toe of soil mass mixed with water retaining agent have maintained a relatively low level,indicating that the addition of water retaining agent can effectively improve the stability of slope under conditions of medium to high water content.With the addition of water retaining agent,the displacement at the bottom of the slope is significantly reduced compared to the soil without water retaining agent under medium and high water content conditions.When the water content is at a low level,the incorporation of water retaining agent will slightly reduce the stability of the slope;When the water content is at a medium to high level,it can effectively improve the slope stability. |
