Effects Of Clay Content On Water Transport In Silty Clay-sand Capillary-barrier Covers

The main function of landfill capping is to avoid direct contact between the garbage body and the atmosphere,reduce the infiltration of rainfall and ensure the stability of the landfill.The traditional covering layer mainly includes compacting clay structure and composite geostructure.Both of the two covering layer rely on the low permeability of the material to prevent the infiltration of water,which is easy to cause the overall failure of the structure due to cracking in the long-term use process,and the cost is expensive.Based on the principle of evapo-transpiration,the capillarybarrier cover is composed of two layers of soil,which can be obtained from local materials,has low engineering cost,and has good long-term service performance.In humid areas,silty clay is widely distributed,and the clay content has a significant influence on the soil-water properties of silty clay.Therefore,it is important to study the influence of clay content on water transport in capillary-barrier cover of silty claysand,which can provide reference and theoretical support for practical engineering.In this paper,six silty clays with different clay contents were analyzed from a silty clay sample of a pivot bank slope in a humid area.Firstly,the soil-water characteristics of the silty clays were studied and the related soil parameters were obtained.Further,the water transport of the capillary-barrier cover of silty clay under different rainfall was investigated by numerical simulation,and the suitable range of clay particle content under heavy rainfall was determined.Finally,the climate conditions in Changsha in 2018 were selected as the boundary conditions of the simulation,and the basic law of water transport and service performance of the capillary-barrier cover of silty clay with different clay content under humid climate conditions were analyzed,and the range of clay content under long-term climate was determined.The main research contents and conclusions are as follows:(1)Study on water storage capacity of silty clay layers with different clay content.The mechanism of capillary-barrier covers and the soil-water characteristic curve of silty clay were studied.According to the test results,the higher the clay content,the smaller the saturated permeability coefficient,the higher the saturated volumetric water content,and the higher the volumetric water content under the same pore water pressure.According to the design theory of storage capacity,the water storage capacity of six silty clays was obtained.The average water storage capacity of monolayer No.6 clay was increased by 21.4%compared with No.I clay.After the formation of capillary arrest effect,the water storage capacity of monolayer No.6 clay was increased by 25.2%compared with No.1 clay,and the same soil structure was increased by 48.9%.(2)Numerical simulation study under rainfall.Combined with the numerical simulation software Seep/W,the lateral diversion capacity and the cumulative leakage at the bottom of the capillary-barrier cover of silty clay under uniform heavy rainfall were studied.The results show that the silty clay with higher clay content has higher water storage capacity and smaller leakage.When the clay content was higher than 32.2%,the capillary-barrier effect was not completely invalid.Compared with the uniform pattern,the leakage generated by advanced pattern is larger,and the leakage generated by the latter pattern is higher than the middle pattern,the advanced pattern is higher than the uniform type.Before the advanced pattern intensity,the leakage generated by the rain type with more cumulative rainfall is higher.(3)Numerical simulation study under the effect of evaporation-infiltration.According to the climate conditions in Changsha area in 2018,the water transport of capillary-barrier effect of silty clay with clay content of 32.2%,37.4%and 45.2%was studied by Vadose/W.The results show that the surface soil at the same location is most affected by climate,and the higher clay content,the more obvious effect of evaporation.Water displacement at the top of the slope>middle of the slope>foot of the slope;The silty clay material with 32.2%clay particle content produced twice as much seepage as the other two materials.The silty clay material with 37.4%clay particle content and 45.2%clay particle content produced similar seepage under the climate in Changsha in 2018,which match the conditions of annual leakage.When the clay content of silty clay is higher than 32.2%,the fine soil layer of silty clay material as capillary block overburden can adapt to the climate conditions in Changsha area in 2018.