Study On The Influence Of Excavation Of Foundation Pit On Bearing Behavior Of Adjacent Flexible Pile Composite Foundation

With the rapid development of urbanization in China,the number of old city reconstruction projects has increased as one of the urban high-quality development routes.As a result,more and more foundation pit projects adjacent to the flexible pile composite foundation.There are many requirements for excavation of foundation pit around flexible pile composite foundation.Therefore,the influence of foundation pit excavation on adjacent flexible pile composite foundation has become an important research task to ensure the safety of buildings on the foundation.At present,the research on the change of the bearing behaviors of adjacent flexible pile composite foundation caused by foundation pit excavation is relatively insufficient.This paper used indoor model test and numerical simulation to study this problem.In this paper,through control the displacement modes of the retaining wall(foundation pit retaining structure)to simulate the excavation of the foundation pit in the actual project,an indoor model test is established.The test focuses on monitoring the stress of the flexible pile body and the settlement deformation of the flexible pile composite foundation,through the comparative analysis of the two sets tests,the law of the force and deformation of the flexible pile composite foundation during the excavation and unloading of the foundation pit are obtained.The ABAQUS is used for numerical simulation,supplement and comparative analysis of the model test results,and using single factor variation method to study the impact of key factors on the change of bearing behaviors of adjacent flexible pile composite foundation caused by the excavation of the foundation pit.Through the above two parts of research,the main research results are as follows:(1)The retaining wall is displaced,and the soil after the retaining wall is settling and deforming,and the relative displacement between the pile and the soil occurs.The load borne by soil is reduced,and the load borne by the pile body is increased.The force of soil around the pile on the flexible pile is change,and the load transmission of the flexible pile to the surrounding soil is weakened.Therefore,the axial force of the pile body gradually increased with the increase of the displacement of the retaining wall.(2)The displacement mode of the retaining wall will directly affect the development process of the soil slip surface.During the rotation of the retaining wall,the relative displacement of the piles and soil in the front row is relatively large,the negative friction area of the pile side gradually increased,the position of the neutral point moves down,and the point of maximum axial force of the pile body moves down;During the translational of the retaining wall,the relative displacement of the piles and soil in the rear row of piles is relatively large,the negative friction area of the pile side gradually increased,the position of the neutral point moves down,and the point of maximum axial force of the pile body moves down.(3)During the displacement of the retaining wall,the horizontal displacement of the pile top increased with the increase of the displacement of the retaining wall,and the horizontal displacement of the pile top of the front row of piles is larger than that of the rear row of piles.Due to the different development trends of the soil slip surface,During the rotation of the retaining wall,the composite foundation loading plate has a large vertical displacement near the retaining wall,and the loading plate appears counterclockwise rotation;During the translational of the retaining wall,the composite foundation loading plate has a large vertical displacement away from the side of the retaining wall,and the loading plate appears clockwise rotation.(4)The change of the distance between the foundation and the retaining wall,the change of the pile length and the change of the pile modulus will all affect the settlement deformation of the flexible pile composite foundation.Increasing the distance between the foundation and the retaining wall,the length of the pile and the modulus of the pile can be obvious reduced the settlement deformation of the composite foundation.Before reaching the critical value,the settlement deformation of the composite foundation decreases with the increase of this factor;when a certain critical value is reached,with the increase of the factor,the settlement deformation of the composite foundation basically does not change.