Finite Element Analysis Of Large Strain Of Foundation Improved By Preloading Method

In recent years, the construction of high speed railway develops rapidly, and a large part ofthese railways need to pass through the southeast coastal area where soft clay can be seeneverywhere, how to control the settlement in soft foundation after construction is always animportant research project in the field of geotechnical engineering. As a kind of economical andefficient, fast and reliable method for soft foundation consolidation, preloading method has beenwidely used at home and abroad; however, due to the intrinsic characteristics of soft clay, it iseasily deformed largely under a high load condition, and sometimes its deformation may go beyondthe applicable scope of traditional small-strain consolidation theory. Therefore, it is necessary tointroduce the relevant theories of large-strain consolidation. Nevertheless, among the existingresearch literatures, there has been little study on the variation rules of soil mass in foundationwhen the impact of large-strain is taken into consideration under the method of vacuum-surchargepreloading. For this, based on a number of research results and with the help of finite elementmethod, this paper analyzed the variation rules of large-strain consolidation when the preloadingmethod is used for consolidated the foundation, and it also studied the large-strain of foundationimproved by dynamic compaction method. The main content and results are shown as follows:(1) In theory, it further elaborates and summarizes the consolidation mechanism of preloadingmethod as well as the simplified calculation method for group wells foundation, and meanwhile, italso deduces and sums up the finite element form of large-strain consolidation control equationbased on the descriptions of Updated Lagrangian and Arbitrary Lagrangian Eulerian, respectively.(2) By combining with ABAQUS, it builds up the three-dimensional large-strain finite elementmodel for single well foundation based on Arbitrary Lagrangian Eulerian description, moreover, theanisotropy and vertical nonlinearity of soil permeability coefficient are taken into consideration, italso researched the impact of different loads and rates of loading on the variation rules oflarge-strain consolidation for single well foundation. The calculation results exactly test and verifythe correctness and rationality of research method in this paper.(3) Based on two engineering projects, the finite element models of large-strain consolidationin group wells foundation based on the descriptions of Updated Lagrangian and Arbitrary Lagrangian Eulerian are established respectively, and meanwhile, cam-clay model (UpdatedLagrangian description) and elastic model (Arbitrary Lagrangian Eulerian description) arerespectively adopted for soil in group wells foundation, this paper also carried out the research onthe variation rules of large-strain consolidation in group wells foundation under vacuum-surchargepreloading (Updated Lagrangian description) and vacuum preloading (Arbitrary LagrangianEulerian description), and makes the comparison on the calculation results of measured value andsmall-strain theory. From the research results in this paper, the calculation result of finite element ismuch closer to the measured value when the impact of large-strain is taken into consideration.(4) By means of dynamical analysis method, the large-strain of finite element model isestablished when the method of dynamic compaction is used to consolidated the foundation, thispaper analyzed the variation rules of settlement by single compaction under different workingconditions, and its effect of consolidation has been compared with that by the method of preloading,and from the results, it can be seen that the effect and depth of consolidation by the preloadingmethod is better than that by dynamic compaction method when improved the foundation with deepsoft clay layer.