Research On Deformation Characteristics Of Foundation Pit Considering Pile Under Overload

At present,due to the shortage of urban land,in order to meet the urban land use,the global urban construction has been widely used underground space to achieve a variety of functions,such as the basement of high-rise buildings,underground stations,underground garages,etc.All kinds of underground facilities involve various deep foundation pit projects.Deep foundation pit engineering is often in the center of a prosperous city,and the surrounding environment is very complex.Usually,there are various buildings around the foundation pit.This puts forward higher requirements for foundation pit engineering.While ensuring its strength,it must also meet the requirements of deformation.A large number of engineering practices have found that the deformation inhibition effect of foundation pit is more significant when there are engineering piles at the bottom of the pit,and the engineering piles have a positive impact on the deformation of foundation pit.Therefore,this paper adopts the research methods of model test,theoretical analysis and numerical simulation to study the foundation pit deformation of engineering piles under the overload and the influence degree of related parameters on the foundation pit deformation.The details are as follows:(1)In order to deeply study the deformation law of foundation pit considering engineering piles under overload,based on the similarity theory,a laboratory model test of foundation pit with engineering piles under the action of overload was designed and carried out.The deformation law of foundation pit with and without overload when engineering piles are not considered is compared and analyzed,and the deformation law of foundation pit with and without overload when engineering piles are considered is compared and analyzed.The test results showed that when there was overload,the engineering pile had little effect on reducing the surface settlement of the top of the pit,followed by the control of the lateral displacement of the supporting structure,and the best effect on reducing the rebound at the bottom of the foundation pit.(2)The calculation method of surface settlement deformation of foundation pit was summarized.On this basis,the foundation pit was regarded as a plane strain problem,and the surface settlement of foundation pit under overload was solved theoretically.The distributed load acting on the soil at the interface of the supporting structure was obtained by the skew-symmetric mapping method.The horizontal additional load acting on the soil at the interface of the supporting structure was obtained by Boussinesq solution.The vertical displacement at any point in the elastic semi-infinite plane can be calculated by the vertical displacement solution.Then,the vertical displacement under additional load was obtained by Boussinesq-Flamant solution.Finally,the calculation method of surface settlement under overload was obtained by superposition principle.The algorithm proposed in this paper was verified by engineering examples and model tests.(3)The calculation method of rebound deformation at the bottom of foundation pit was summarized.Based on the existing theory,the calculation method of rebound at the bottom of foundation pit was improved.Without considering the pile weight,under the condition of pile-soil displacement coordination and pile stress balance,and based on the layer-wise summation method,the Mindlin solution and the existing calculation methods of pile-soil displacement,the rebound deformation of the soil at the bottom of the pit caused by the excavation unloading of the foundation pit was studied and the calculation method of soil rebound under the existing of engineering pile was proposed.Finally,the calculation results of the proposed method and the finite element simulation results were compared and analyzed with an engineering example.And it was proved that the improved method is reasonable.(4)Through the control variable method and numerical analysis software,the influence law of many parameters on the foundation pit deformation was studied,and the influence law of overload three factors,pile diameter,pile length and pile spacing on the foundation pit surface settlement and bottom rebound was analyzed.It was found that the magnitude and location of overload action have significant influence on the surface settlement,and reducing the distance between piles can significantly reduce the rebound of foundation pit bottom.