The Simulation Research On Pile-raft Combination Foundation Reduce Differential Settlement

Pile-raft combination foundation has good sink, leveling performance, and theeconomy is good. In order to reduce differential settlement as the main purpose of thevariable rigidity design is the key points in the pile-raft combination foundation design.However, in the traditional pile-raft combination foundation design, the upper structureload assumed by the pile directly, failed to give full play to the raft board share,conservative design, easy to cause waste and other secondary problems. In this paper,on the basis of previous research results, focusing on the pile-soil-raft interaction ofpile-raft combination foundation effectively solve the problem of differential settlement,the application of numerical simulation for analysis and discussion.This paper focused on the following aspects of the work:(1)The soil respectively the Mohr-Coulomb model and linear Drucker-Pragermodel, comparison of two different constitutive model of soil under the raft ofsettlement. Prove that the parameters of the two models in three-dimensional problemstransformation formula is correct.(2) Using the ABAQUS finite element analysis software, establish the pile-raftcombination foundation model, the analysis of a variety of pile layout, pile length, raftthickness, soil elastic modulus and variable stiffness cushion layer influence ondifferential settlement of foundation, it is concluded that under the premise of carryingcapacity satisfy, central pile layout can well reduce the foundation differentialsettlement.(3) Adjust the pile spacing and pile length can reduce differential settlement andeconomic benefit is good. The average settlement and differential settlement decreaseswith the increase of soil between piles and pile end soil elastic, and reduce theamplitude decreases gradually. With variable stiffness cushion layer under the raft ofelastic modulus ratio increases, no pile raft foundation and uniform full pile foundation differential settlement decreases, and reduce the effect is not obvious more and more,under the raft with variable stiffness cushion layer can effectively reduce the foundationdifferential settlement.(4) In combination with the project example, the use of ABAQUS simulationanalysis. Using the calculation results, several improvement schemes are put forward onthe project example. It is concluded that at the top of pile add the cushion can reducethe load of pile top, develop the bearing capacity of foundation soil. For the complexfoundation in karst, soil hole, in the upper structure load set large area increases thevertical pile stiffness (the anti reduction) and under the raft with variable stiffnesscushion layer, the combination of two methods can be more effectively andeconomically reduce the differential settlement of foundation.