Working Mechanism And Load Transfer Mode Of Pile-Supported Reinforced Embankment In Soft Soil Area

In the construction of traffic network,subgrade engineering will inevitably cross the bad geological sections such as soft soil.As a new type of foundation treatment,pile-supported reinforced embankment can increase the horizontal resistance of the system,increase the pile spacing and reduce the project cost by arranging geosynthetics on the top of the pile.The working mechanism of pile-supported reinforced embankment is complex,and its core working principle is based on the soil arching effect of embankment filler caused by differential settlement between pile and soil and the membrane effect of flexible reinforced materials in cushion.At present,due to the different assumptions of soil arch form and reinforcement deformation in each calculation model,the calculation results are quite different.And the assumptions of the existing theoretical calculation methods are quite different from the actual working conditions.For example,the influence of cohesion of embankment filler is not considered in the analysis of soil arching effect,and the coupling effect of soil arching effect and membrane effect is not considered in the calculation of embankment load distribution.Through indoor model test,finite element numerical simulation,theoretical analysis and field test,this thesis deeply studies the bearing mechanism and deformation characteristics of pile-supported reinforced embankment,improves the load distribution calculation method,and provides theoretical support for promoting the application of this technology in engineering construction.The main research contents and results are as follows.(1)Evolution mechanism of soil arching effect of pile-supported reinforced embankment considering the influence of cohesion of embankment fillerBased on indoor model test and finite element numerical simulation,the formation and evolution mechanism of soil arching effect in cohesive soil embankment is systematically studied.The influence modes of embankment height,cohesive soil strength characteristics,pile spacing,pile-soil differential settlement and other factors on soil arch effect and soil arch shape are revealed.The results show that the degree of soil arching effect is related to the development law of arch axis.The shape of the arch axis is approximately parabolic.The maximum height of the soil arch between the two piles is 1.10 (S-a) a S-,and the maximum height of the soil arch between the four piles is 1.16 (?)(S-a).The large principal stress vector diagram shows that there are still a series of arch rings inside the soil arch,and the soil arch shape is similar to the concentric arch model and the multi-arch model.(2)Spatial distribution characteristics of reinforcement deformation of pile-supported reinforced embankmentBased on the indoor model test and finite element numerical simulation,the deformation law of reinforcement material at each measuring point between piles and pile caps is systematically studied,and the spatial distribution characteristics of stress and strain of reinforcement material in reinforced cushion under the action of various influencing factors are discussed.The results show that: The differential settlement of pile and soil is the main reason for the deformation of reinforcement.The deformation of reinforcement at the edge of pile cap is most affected by the differential settlement of pile and soil,followed by the center of two piles and the center of four piles.The tensile strain distribution of the reinforced material is uneven.The deformation at the edge of the pile cap is the largest,and the deformation at the top of the pile cap is the smallest.The deformation of the reinforcement at the center of the two piles is far greater than that at the center of the four piles.The deformation law of reinforcement material shows that the reinforcement material in the central area between adjacent two piles and four piles can bear and transfer the embankment load.Therefore,it is suggested that the contribution of reinforcement material between four piles to load transfer should be considered when analyzing the membrane effect.(3)Calculation method of load distribution of pile-supported reinforced embankment considering the influence of cohesion of embankment fillerBased on the applicability evaluation of various soil arch models in the relevant specifications of pile-supported reinforced embankments at home and abroad,an optimization technique based on the "concentric circular soil arch" model is proposed.The calculation method of load distribution of pile-supported reinforced embankment considering the influence of cohesion of embankment filler is constructed,and the mechanical calculation and analysis model of membrane effect considering the interaction between reinforcement and cushion is proposed.The calculation formula of load distribution considering the influence of cohesion of embankment filler and the combined action of soil arch effect and membrane effect is derived.(4)Study on mechanical behavior of pile-supported reinforced embankmentBased on the field test and finite element numerical simulation of pile-supported reinforced embankment of Rongwu Expressway in Xiong ’an New Area,the mechanical behavior of pile-supported reinforced embankment in soft soil area is studied.The influence of embankment height,pile spacing and cushion form on load transfer and foundation settlement is further clarified.The results show that:Increasing pile length,pile spacing,embankment height and reducing pile cap side length can promote the soil arching effect to a certain extent.The increase of tensile strength of reinforced materials has a certain promoting effect on load transfer.Subgrade settlement analysis shows that the settlement of the underlying layer accounts for 67.9 % ～ 74.1 % of the total settlement,and the settlement of the reinforcement area accounts for a small proportion.Increasing pile length,pile cap side length,reducing pile spacing and reducing embankment height can effectively reduce foundation settlement and improve embankment stability.