Deformation Mechanism And Settlement Calculation Of Geosynthetic-Encased Stone Columns-Supported Embankment With Basal Reinforcement

The bearing capacity of a stone column is determined by the lateral restraint provided by the surrounding soil.When the undrained strength of the surrounding soil is less than15 k Pa,the lateral confinement may be insufficient,resulting in failure due to excessive bulging.Wrapping or encasing stone columns with geosynthetic material,known as geosynthetic-encased stone column(GESC),is an effective technique for preventing excessive granular column bulging while retaining drainage performance.In addition,embankment with basal reinforcement or geosynthetic reinforced embankment is commonly used in practice to reduce differential settlement of the embankment and increase embankment stability.The GESCs have been successfully used in embankments or dams and other projects,and many studies have been conducted to focus on the behavior of end-bearing GESC-supported embankments.However,there has been no investigation into the floating GESC-supported embankment,and the behavior of geosynthetic reinforced embankment over end-bearing and floating GESCs is still unknown.Therefore,in this paper,a series of centrifugal model tests and 3D hydro-solid coupling FEM numerical modeling were conducted to reveal the deformation mechanism of GESC-supported embankment,and based on that,the settlement calculation method of GESC-supported embankment was developed,taking into account the effect of basal reinforcement stiffness and substratum soil stiffness.The main work and research results of this thesis are as follows:(1)The constant acceleration centrifugal model tests were conducted to study the displacement vector field,pile-soil load transfer,excess pore water pressure,and strain distribution of basal reinforcement in the end-bearing GESC-supported embankment with and without basal reinforcement.The test results show that the basal reinforcement significantly increased the stability of the end-bearing GESC-supported embankment.For the without basal reinforcement case,the deep slip failure surface occurred in the end-bearing GESC-supported embankment,which was composed of the Rankine surface in the embankment and the arc sliding surface in the foundation.In addition,the basal reinforcement significantly reduced the total and differential settlement,and lateral displacement near the toe,and prevented the bending deformation of the GESC.Furthermore,the basal reinforcement increased the stress on the GESC and reduced the stress on the surrounding soil,thereby reducing the generation of excess pore pressure in the foundation and increasing the stress concentration ratio(SCR).For example,when compared to the case without basal reinforcement,the SCR of the case with basal reinforcement increased by 28%.Besides,because the tensiled membrane effect of the basal reinforcement under the top surface of the embankment is greater than that under the side slope,the tensile strain of the basal reinforcement under the top surface of the embankment is significantly greater than that under the side slope,and the strain of the basal reinforcement under the embankment shoulder is the greatest due to the basal reinforcement under the shoulder being tensioned by the embankment laterally expanding.(2)The variable acceleration centrifugal model tests combined were conducted to study the effect of basal reinforcement on the displacement vector field,pile-soil load transfer,excess pore water pressure,and strain distribution of basal reinforcement in the floating GESC-supported embankment with basal reinforcement.The test results show that the basal reinforcement significantly reduced the total and uneven settlement in the floating GESC-supported embankment,and lateral displacement near the toe.However,the basal reinforcement increased the lateral displacement at the middle and bottom parts of the floating GESC,causing the floating GESC to bend inward of the embankment.Furthermore,when compared to the case without basal reinforcement,the SCR of the case with basal reinforcement increased by 10.7%.(3)Based on the centrifugal model test,a 3D hydro-solid coupling FEM numerical model of the floating GESC-supported embankment with basal reinforcement was established.The effect of the basal reinforcement on the deformation of the floating GESC-supported embankment,SCR,and the hoop strain of the encasement was investigated.The results show that the floating GESC-supported embankment has the neutral point,while the depth of the neutral point was significantly reduced due to the inclusion of the basal reinforcement.The basal reinforcement increased the SCR at the column top near the embankment centerline,thereby causing the increase of the penetrating deformation into the substratum.In addition,the basal reinforcement reduced the bending deformation of the pile near the toe,so the encasement hoop strain of the case with basal reinforcement was significantly smaller than that of the case without basal reinforcement.(4)The 3D hydro-solid coupling FEM numerical model for the prototype floating GESC-supported embankment with basal reinforcement was established to investigate the effect of governing factors on the deformation of GESC-supported embankments,such as the consistency of the substratum soil,stiffness of basal reinforcement and encasement,and embankment height.The results show that the surrounding soil carries more embankment load due to the weaker substratum soil,which leads to reduce the SCR,thereby increasing the global settlement and lateral displacement of the floating GESC-supported embankment.The increase in stiffness of the basal reinforcement and encasement caused more embankment load transferred on the GESC,and increased the SCR of the floating GESC-reinforced foundation,thereby reducing the global settlement and lateral displacement of the embankment.(5)The mechanical analysis model of the GESC-supported embankment with basal reinforcement was established,and a settlement calculation method for the settlement of the GESC-supported embankment with basal reinforcement was proposed,considering the influence of factors such as the stiffness of the reinforced cushion and substratum,deformation of column top penetrating sand cushion,deformation of column bottom penetrating substratum,column-soil friction,and bulging deformation of GESC.The calculated settlement obtained by the method in this paper,the composite modulus method,and the EBGEO method were compared with the results of the field case,centrifugal test,and 3D numerical modeling,respectively.The results show that the relative calculation error of the method in this paper is smaller than that of the composite modulus method,and EBGEO method.