Landslide Mechanism Of Accumulated Layer Under Rainfall Research On Stability Impact

As a natural geological hazard,landslide often causes huge loss of life and property.China is a country with frequent landslide disasters.It is one of the important means to reduce landslide disasters to make early prediction and take effective preventive measures.The prediction criterion is the core of landslide prediction,but it is relatively difficult to establish the prediction criterion.Many experts and scholars at home and abroad have studied and established a large number of prediction criteria,and have successfully predicted the specific landslide,but each prediction criterion has certain limitations,so it is difficult to find a unified quantitative index and quantitative standard.Therefore,the study of landslide prediction and prediction is necessary Based on the landslide type,characteristics and formation mechanism,it is necessary to study and analyze the specific landslide and find out the main factors affecting the stability of the landslide,so as to obtain the practical and feasible prediction criteria of the landslide.Tangjiao No.1 landslide is a loose accumulation type landslide.With the increase of water level in the Three Gorges Reservoir and the influence of perennial rainfall,cracks have begun to appear in the local position,and the landslide body is also in a potential unstable state.By studying the deformation characteristics and failure mechanism of the landslide,it can be seen that the main factors causing the landslide instability and deformation are continuous water storage,rainfall and sudden drop of reservoir water level in the Three Gorges Reservoir area.Based on the research background of Tangjiao No.1 landslide in Wanzhou District of the Three Gorges Reservoir Area,this paper mainly studies the mechanism and stability of the accumulation layer landslide under rainfall conditions.In order to study the stability of the landslide,the physical model test of indoor slope was carried out with Tangjiao No.1 landslide as the research object.By monitoring the change of soil pressure,pore water pressure and moisture content inside the slope body,the influence of slope stability under rainfall conditions was further analyzed.At the same time,the effects of moisture content,matric suction,saturation,rainfall intensity,rainfall holding time and total rainfall amount on slope stability were further discussed.The main findings are as follows:(1)Effect of rainfall infiltration on slope mechanism.Under the action of rainfall conditions,the moisture content in unsaturated soil increases,the soil tends to be saturated continuously,and the pore water pressure increases,which leads to the decrease of shear strength and safety coefficient of unsaturated soil,which affects the stability of slope.Under the same slope and the same boundary conditions,the saturated-unsaturated seepage field during rainfall infiltration is mainly affected by the rainfall type,rainfall intensity,rainfall holding time and other factors.(2)Laboratory physical model test and slope stability study.with the rainfall intensity of 93.3 mm/d,the infiltration influence range is increasing with the increase of rainfall duration,and the rainfall influence depth range is about 0.3 m,which indicates that even in landslide areas without cracks,voids or sliding surfaces,the rainfall type with relatively high rainfall intensity may induce shallow landslides.At the beginning of the rainfall,a large amount of loose soil layer was taken away by the erosion and erosion of rain water.At this point,soil pressure and pore water pressure are not broken rise,so that the matric suction began to decline,that is,after the rainfall lasted 40 minutes,with the increase of rainfall duration,the slope load began to increase,and the possibility of instability was also greater.(3)Study on the influence of rainfall infiltration law.In this laboratory physical model test,under the influence of rainfall,the moisture content percolates down,but the change of water content at each point inside the soil is different,and the change of water content is large,which is also the most intense area of soil movement,which indicates that the water content has a great influence on the damage of soil.Firstly,the increase of water content will increase the pore water pressure and decrease the effective stress,which will lead to the decrease of the shear strength of the soil;secondly,the increase of water content will make the permeability of water and the heavy soil increase,which will lead to the decrease of the stability of the slope and the double effect.Down is one of the causes of landslides caused by rainfall.(4)Numerical simulation of slope stability under rainfall conditions.When the rainfall duration is the same,the greater the rainfall intensity,the greater the safety factor decreases,but the stability coefficient of the slope is not significantly reduced,mainly because the rainfall intensity at this time is greater than the actual infiltration capacity of the soil,and the increase of rainfall in the later period is only in the form of surface runoff,and the actual infiltration amount has not changed significantly.(5)Effects of rainfall intensity and rainfall on slope stability.it is recommended to use rainfall intensity and accumulated rainfall as the parameters required for rainfall warning benchmarks,where rainfall intensity parameters can be expressed in the form of hourly rainfall,and accumulated rainfall can help assess landslide disasters.When the initial conditions are relatively close,there is a close relationship between the initial landslide produced by the slope and the accumulated rainfall,that is,there is a "critical cumulative rainfall" in the rainfall type landslide,and when the accumulated rainfall exceeds this critical cumulative rainfall,it may be more prone to landslide damage.