Study On Behavior Of Pile Groups In Completely Saturated Porous Elastic Medium

The behavior of pile groups in a completely saturated porous medium is an important problem in geotechnical engineering. The piled raft system with a thick soft substratum, considering the consolidation of the substratum, was studied in this paper. The development with lime of raft internal force, deformation and pile butt load was obtained.It is very important to evaluate the stiffness of single pile in pile groups in the analysis of pile foundation. The pile top settlement is mainly made up of the pile compression and the pile tip settlement caused by the consolidation of the substratum. Hence the stiffness of single pile in pile groups is related to the consolidation of the substratum. For simplifying the analysis, the soil layer within pile length was simplified as a permeability field and as an impeded boundary of the substratum. The pile tip settlement was obtained by adopting the solutions of three-dimensional consolidation problems with impeded boundaries. Thus, the stiffness with time of sing pile in pile groups can be determined. Therefore, axisymmetric solutions for a semi-infinite clay stratum and a finite clay layer with impeded boundaries were derived. Laplace and Hankel integral transforms were utilized with respect to time and radial coordinates in the analysis, respectively. The derivation of fundamental solutions considered two boundary-value problems involving unit point loading and ring loading in the vertical, and the fundamental solutions have been extended to circular, strip and other distributed normal load.In order to reveal the stress and permeability field of the vertical loaded piled raft system and verify the reliability of the presented method, the first, both capacity and displacement behavior of vertically loaded single pile in a saturated porous medium were analyzed by the finite element methods respectively. The change of pile tip settlement, axis force in pile, shear stress around pile and the initial excesspore pressure, considering the soil consolidation, were studied. The major part of the final settlement of a single pile is immediate settlement, and occurs on application of the load because the load is transferred to the soil essentially by shear. The second, the behavior of piled raft foundation was studied by simplified linear elastic plane strain finite element method, and the initial excess pore pressure distribution and its dissipation were studied. It is showed that the permeability is two-dimensional in the substratum and one dimensional within the area of the pile length. Last, comparing the plane strain solutions for finite layer with impeded boundaries with finite element result, the stress and permeability field were verified.A calculating model for the consolidation settlement of piles group was built by approximately simulating the stress and permeability field of vertically loaded piled raft foundation. The effective and total stress formula of within substratum was obtained by applying the consolidation solutions with impeded boundaries. The pile tip settlement can be evaluated by layered superposition method. Thus the stiffness of single pile in pile groups can be obtained in any time. Then agglomerating it to the boundary of raft, the raft was analyzed by finite element method. Analyzing software of pile-soil-raft interaction (POGAP) was developed. Two case studies were also carried out to show the application of the present method to practical pile group problems.