Experimental Study On Failure Mechanism Of Loess Slope Under Rainfall And Evaporation

Loess is widely distributed in our country.The loess area is mainly in the arid and semi-dry climate zone,and the loess is continuously circulated in saturated and unsaturated state due to rainfall infiltration and evaporation.In this dynamic cycle,there will be a series of effects on the physical and mechanical parameters of the soil,pose a threat on the safety and stability of the structure,resulting in landslides,slope erosion and other disasters.Therefore,the changes law study of soil physical and mechanical parameters in the rainfall-evaporation process,it is of great significance to explore the mechanism of loess slope failure from the change of physical and mechanical parameters of soil.Based on the study and summarization of previous studies on the stability of unsaturated loess and slope,a series of physical mechanics tests were carried out in Lanzhou loess,which studied the change law of physical and mechanical properties under had different water content and wet and dry cycle in Lanzhou loess.And through the numerical simulation,the seepage law of slope and stability during the rainfall was explored,and achieved some research results.Firstly,the physical properties of perturbed Lanzhou loess were measured by making sample of them,including particle size gradation curve,optimal water cut rate,liquid limit and plastic limit.The Fredlund soil-water characteristic curve pressure plate was used to determine the Lanzhou loess soil-water characteristic curve.Secondly,the shear strength index of Lanzhou loess under different water cut and dry-wet cycles was studied by direct shear test,and the influence of wet and dry cycle on the permeability coefficient of Lanzhou loess was studied.It is found that with the increase of soil moisture content,the shear strength of soil increases first and then decreases,and the maximum shear strength appear when the water content at 12%.The cohesive force increases first and then decreases with the increase of water content,and reaches the maximum when the water content is 16%.With the increase of water content,the internal friction angle tends to be stable after slow decrease.The shear strength of soil decreases continuously with the wetting drying process,but the overall change is not significant.Rainfall makes the slope's stability decline,and soil particles on the slope are easily swept away by the rain,resulting in destruction of the slope,and rainfall is easy to cause shallow slope collapse.The wetting and drying process reduces the cohesive force of the soil rapidly,and the cohesion basically unchanged after 4 cycles of dry and wet cycles.During dry and wet cycles,the angle of internal friction increases slowly,and remains stable after 2 cycles of wetting and drying.The permeability coefficient of the soil increases with the wet and dry cycle,and the permeability coefficient increases after the first wet and dry cycle.The stability of the slope after the wet and dry cycle decreased,the rainfall further reduced the stability of the slope,the slope of the slope at this time prone to damage;slope excavation after the first few times the most likely to damage the evaporation process.Slope permeability coefficient increases,the impact of rainwater infiltration also increases,which is an important reason for slope damage.Finally,using the measured soil water characteristic curve,the infiltration process of loess slope under different rainfall conditions was simulated by Geo-Studio software.The coupling analysis of seepage and ultimate equilibrium was carried out to study the influence of water infiltration on the slope stability under different rainfall conditions.It is found that the pore water pressure and volume water content of the slope soil are increasing with the increase of rainfall intensity,and this effect is more and more obvious.The depth of impact of different rainfall intensity on volume moisture content and void water pressure is about 2m,but with the increase of rainfall intensity,the influence degree of slope is also increasing.No matter what the rainfall conditions,after the rainfall reaches 72 hours,the slope safety factor is reduced.Under the rain intensity of moderate rain conditions,the slope stability of different slope is decreased,and the slope gradient is bigger,the slope stability coefficient is more small,and more sensitive to rainfall infiltration.