Study On Mechanical Behavior Of Pile-sheet Wall On Expansive Soil Slope And Design Of Expansion Reducing Layer Behind The Wall

When the pile-sheet retaining wall(hereinafter referred to as pile-sheet wall)is used for the support of expansive soil slope,its displacement capacity is poor due to the large section size of the pile and sheet.Huge lateral swelling pressure will be generated behind pile-sheet wall,which affects the stress state of pile-sheet wall structure and its service safety.Therefore,how to reduce the lateral swelling pressure behind pile-sheet wall has become a research hotspot in recent years.In this thesis,relying on the National Key Research and Development Program(2019YFC1509800),through literature research,field test and numerical simulation,this thesis carries out the research on the mechanical behavior of the pile-sheet wall of the expansive soil slope and the design of the anti-swelling pressure layer behind the wall.The main research contents and results are as follows:(1)The basic physical and mechanical properties and microstructure of typical expansive soils in Guangxi and Hubei provinces are studied.It is pointed out that the soil particles of the typical expansive soils in the study are all stacked.In addition,the expansive deformation characteristics of expansive soils are also tested.It is concluded that the expansion force can be effectively reduced by releasing the expansion displacement of the expansive soil.(2)It is proposed that the lateral swelling force behind the Pile-sheet wall is triangular,and the maximum value of the lateral swelling force is near the position where the atmosphere strongly affects the depth.On this basis,combining theoretical and numerical analysis,the mechanical behavior and structural control parameters of Pile-sheet wall structure supporting expansive soil slope are studied and analyzed.It is considered that the spacing between Pile and Pile in expansive soil area is 4～6 m,the height of cantilever section of common Pile-sheet wall should be no more than 8 m,and the stress of Pile-sheet is greatly affected by water seepage at the bottom of cantilever section.The anti-seepage and moisture retention at the bottom of cantilever section should be paid attention to.At the same time,the flexible material has the characteristics of low elastic modulus and easy deformation,which can give more expansion space to the expansive soil.Therefore,measures are put forward to lay a certain thickness of flexible expansion-reducing material behind the Pile-sheet wall to reduce the expansion force acting on the structure.(3)Field tests are carried out on Pile-sheet wall-expanding layer structure of expansive soil slope.By comparing the distribution of earth pressure and structural internal force behind the pile sheet wall with different expansion reducing layer materials,it is concluded that the flexible material can not only reduce the lateral pressure behind the wall and promote the soil arching effect behind the pile,but also make the stress behind the wall more uniform.In the design of pile-sheet wall of expansive soil slope,the reducing effect of expansion reducing layer on lateral swelling pressure should be fully considered.(4)On the basis of the above research,a three-dimensional numerical model of Pile-sheet wall-expansion-reducing layer structure on expansive soil slope is established by using Abaqus software,and the design parameters of expansion-reducing layer are studied.The analysis results show that EPS plates with density greater than 15 kg/m~3 and thickness greater than 30 cm can effectively reduce the lateral swelling force acting on the structure.At the same time,the working performance of expansion-reducing layer under different overlying loads,different lateral swelling forces and different seepage conditions is discussed.Finally,a recommended table for the design of the expansion reducing layer is formed to guide the engineering practice.165 figures,26 tables,103 references...