Research On Double-Layer Soft Clay Ground Improved By Rigid-Flexible And Long-Short Piles

As a filling material,dredger soil is widely applied in sea reclamation to reduce the pressure on the conflict of the rare of land in coastal area.However,the double-layer soft soil foundation,which is formed by dredger fill and natural marine sedimentary soft soil,is a technical challenge in the engineering field.This article relies in Lianyungang port railway project,which in formed by hydraulic fill slurry,and precast square pile and deep mixing column with expanded head are combined to improve the ground.Its reinforcement effect and strengthening mechanism were studied by field test and numerical analysis.On this basis,a practical design and calculation method for rigid-flexible and long-short piles under embankment load is put forward.The main conclusions can be drawn as following:(1)Through the laboratory test,the engineering properties of the dredger fill and the natural marine sedimentary soft soil are compared and analyed from the aspects of physical and mechanical properties.The results show that the engineering properties of the dredger fill is a little weaker than the marine sedimentary soft soil.The test site is a typical double layer soft soil foundation,which has the characteristics of high moisture-content and compressibility,low permeability and underconsolidated.(2)The field test research on the double layered soft soil foundation is carried out with precast square pile and deep mixing column with expanded head.The bearing characteristics of the precast square pile and deep mixing column with expanded head under the load test are clarified.The deformation of the foundation reinforced by the precast square pile and deep mixing column with expanded head under the embankment load is analyzed.The load share ratio of the pile and soil is analyzed,which provides the reasonable basis for the design of the rigid and short pile foundation.(3)ABAQUS software is used to establish the numerical model of rigid-flexible and long-short pile,rigid long pile and flexible short pile.The contribution of rigid long pile and flexible short pile to the improvement of foundation performance is discussed.The reinforcement mechanism of rigid and flexible pile under embankment loading is discussed f soil arch effect and membrane effect.The analysis results show that the rigid long pile is the main structure of settlement and bearing control,and the flexible short pile can significantly reduce the differential settlement of the pile and soil,reduce the stress concentration of the rigid long pile,and improve the bearing capacity of the soil.(4)Based on the numerical model of rigid and long short pile composite embankment,the influence of rigid pile design parameters,flexible pile length,cushion design parameters and subgrade packing design parameters on composite foundation properties are analyzed,and the proposed values of the design parameters are given.Combined with the results of field test and numerical results,a practical design method of rigid-flexible and long-short pile under embankment load are proposed.