Effect On The Infiltration Of The Local Accumulation Of Large Particles And Coarse Particles In Deposits

Due to the influence of origin and evolution process,the structural heterogeneity of deposit is a common sedimentary phenomenon.The inhomogeneity caused by the accumulation of local large particles and coarse particles is one of the common forms.The differential infiltration of rainfall may be an important factor which causes the surface water to infiltrate rapidly into deep soil and triggers the unstable failure of largescale deposits.Based on the field investigation of the landslide deposits on both sides of Tumen River,the particle grain size,structural and sedimentary characteristics of large-scale deposits were investigated in this paper.and three typical local accumulation modes of large particles and coarse particles were summarized.We analyzed the movement of wetting front,the variation of pore water pressure and matric suction during the infiltration of rainfall by using the physical modelling and numerical simulation method,then studied the effect on the infiltration of the local accumulation of large particles and coarse particles.At the end,a landslide,which was triggered to be reactive,was taken as a case to analyzed the effect on infiltration mechanism of local accumulation of large particles and coarse particles in the landslide deposits.Some important results were obtained as follows:(1)More than 50% of the large particles and coarse particles are larger than 60 mm in size,and the large particles and coarse particles are in angular.When they are accumulated in a certain area,they tend to form a dense development area of macropores,which is a structural feature that enables them to gather a large amount of surface water.More than 90% of the local accumulation areas are deposited in the front edge and middle site of the landslide deposits,and about 85% of them are deposited at 10-40 ° slope;(2)In the indoor rainfall physical experiment,the surface water can be gathered by the local accumulation area of large particles and coarse particles,the gathered water infiltrated into the deep soil continuously during the time when the rainfall stops.At this time high pore pressure area was formed in the surrounding soil,and the water was promoted to infiltrate into the surrounding soil by the high hydraulic gradient which was caused by high pore pressure.It resulted in higher water content of the soil under the local accumulation area than that in other areas in physical model;(3)The surface water carrying capacity of the accumulation area can be affected by the distribution form of local accumulation and the area of the slope above it.When the distribution pattern of the accumulation area determined that it cannot gather the surface water,the infiltration of rainfall in the slope was not affected by the local accumulation area of large particles and coarse particles.The larger the slope surface area above the accumulation area,the more surface water was gathered in the local accumulation area after rainfall until it reaches the upper limit of its water carrying capacity;(4)In the physical model experiment,when a large amount of rainwater was gathered in the local accumulation area of large particles and coarse particles,the wetting front of model was also significantly affected: In the process of rainfall,the wetting front was a downward convex circular arc with the accumulation area as the center and expands continuously.But with the infiltration,the curvature of the circular wetting front gradually decreased until it becomes a straight line parallel to the bottom of the experimental model;(5)According to the finite-element method(FEM)based model results of the landslide deposit of Gendakan,a large amount of surface water were gathered in the local accumulation area of large particles and coarse particles under the condition of intense rainfall,and a high pore pressure area was formed below the accumulation area.The higher pore water pressure resulted in higher hydraulic gradient which promoted the gathered surface water in the accumulation area to infiltrate rapidly into the deep soil.When the several accumulation areas' gathered water seeped into the slip zone and forms a through seepage channel between the slip zone and the upper soil,the sliding force of the soil was greatly increased,and the safety factor was significantly impacted.