Research On Application Of The Passive Berms In Front Of Pile In Peat Soil

The passive berms in front of the pile can replace anchor cables and horizontal struts to provide a certain horizontal force and increase the passive earth pressure of the foundation pit.It can reduce the project cost,shorten the construction period and has been widely used in engineering.However,the force analysis of the passive berms in front of the pile is complicated,and the calculation process is complicated.At present,no effective simplified calculation method has been proposed in the industry standard to the passive berms in front of the pile.And the research on the passive berms mostly focuses on clay,silty clay,and silty clay,and rarely involves peat soil,especially to the unique lacustrine sedimentary peaty soil in yunnan is rarely involved.With a vast range of distribution and large thickness,peat soils are basically special soft soils that cannot be avoided in the construction of foundation pits.Therefore,it is of great engineering practice significance to study the application and simplified calculation of the passive berms in front of the pile in peat soil.In this paper,the application of the passive berms in front of the pile in peaty soil is studied,and a simplified calculation method is proposed.Firstly,the mechanical characteristics and distribution of peat support soil were analyzed,and the advantages and disadvantages of different retaining and protecting structures in peat soil were analyzed;Then,the passive berms was simplified to plane strain problem to systematically analyze the influence of pile length,stiffness of support system,geometric shape and whether the reserved soil platform is consolidated or not on displacement and moment.The next,the stress and deformation characteristics and failure modes of the passive berms in front of the pile in peaty soil are summarized,a simplified calculation method of retaining platform is derived based on this.Finally,based on an project case,the usability of the passive berms in front of the pile in peat soil is verified,and the rationality of the simplified calculation method is verified.The main research results include the following aspects:(1)Through compared the displacement and moment of the different excavation depths,such as 7.0 m,8.0 m and 9.0 m.It is considered that the maximum excavation depth in the peat soil of the passive berms should not exceed 8.0 m.However,if the passive berms is stabilized with cement,the excavation depth can be increased to 9.0 m.(2)According to the results of finite element analysis,it is suggested that the width of the passive berms should be 1.2H(H is the excavation depth),and the height of the passive berms should be 0.6H.However,if the passive berms is stabilized with cement,the height of the passive berms can be increased.(3)The failure modes of the passive berms in front of the pile can be divided into two types: one is the overall sliding of retaining structure system through pile bottom,and the other is the single sliding failure of the passive berms in front of the pile.In peaty soil,the width of the passive berms in front of the pile is within 1.2H,and the effective height is within 0.5H,The failure mode is overall sliding of retaining structure system through pile bottom.If the height and width of the passive berms are larger than the above values,the failure mode is the single sliding failure of the passive berms in front of the pile.(4)According to the stress and deformation of the passive berms in front of the pile in the peaty soil layer,it is simplified into a cantilever support system with a certain depth,and the reduction coefficient equations of the height and width of the reserved soil platform are deri ved.