Study On Water Retention Characteristics Of Unsaturated Soil And Slope Stability Under Wetting And Drying Cycles

Soil slopes are often in a wetting-drying cycles,and the properties of the soil are changing during each cycle.At present,the study on the change of soil properties under the wetting-drying cycles is mainly focused on the attenuation of the shear strength of the soil,and the cumulative effect of the change of the water retention characteristics of the soil in the wetting-drying cycles is also important of the slope will directly affect the stability of the slope,which has become one of the main causes of slope instability.In this paper,sand,silt and clay as the object of study,focused on water retention characteristics of soil by the effect of the wetting-drying cycles.On the basis of this,the effect of the change of water retention capacity of soil on the seepage and stability of the slope were considered by using the method of numerical calculation.Secondly,the effects of saturated permeability coefficient,different rainfall conditions and different slope ratio on the seepage field and stability of different soil slopes under wet and dry cycles were analyzed.Finally,the variation law of the seepage and stability of the soil slope before and after the geo-membrane cover was compared,and the feasibility and effectiveness of the geo-membrane cover method were discussed.The main results of this paper are as follows:(1)The wetting-drying cycles cause the change of the water retention characteristics of the soil,and the matric suction of the soil under the same water content became smaller as the number of wetting-drying cycles increased,that is the water retention capacity of the soil irreversible attenuation.Among them,the clay had smallest water retention capacity by the influence of wetting-drying cycles followed by silt,the largest sand.With the increase in the number of wet and dry cycles,the effect of single wetting-drying cycle on the water retention capacity of soil is weakened.(2)Under the wetting-drying cycles,the change of water retention capacity of soil affected the distribution of soil water content and slope stability to a certain extent.Among them,when the rain intensity was large,the decay of soil water retention capacity had a great influence on the seepage and stability of silt slope.When the rain intensity was small,the decay of soil water retention capacity has a great influence on the seepage and stability of clay slope.(3)The influence of the saturated permeability coefficient and the influence of different rainfall conditions on the seepage and stability of different soil slopes dependson the relative relationship between the atmospheric rainfall intensity and the soil permeability coefficient.(4)The effect of geo-membrane cover method on clay slope was better than that of silt slope.For silt and clay slopes,started at about 3m and 1m at the boundary of the membrane cover respectively,and the soil under the membrane was not disturbed by atmospheric rainfall and evaporation.Compared with the slope of the geomembrane,the effect of the geo-membrane laying shap was better than that of the stepped shape.The shorter the length of the geomembrane had the better effect.The clay slope of the above law is the opposite.