Analysis Of Stress Deformation And Design Parameters Of Double-Row Piles In Deep Foundation Pit With Thick Gravel Layer

In recent years,under the requirements of the National Strategic Development,the construction of various projects in the newly emerging second-line medium-and large-scale cities in various regions is still in full swing,especially the growth rate of urban underground projects,with the emergence of a large number of deep foundation pit and super-large Foundation pit engineering.However,urban construction can not avoid the problem of site constraints,and there are strict requirements for the deformation control of foundation pit.A large number of engineering accidents as well as experience and lessons have shown that the basic principles of safety,rationality and economy should be adhered to in the selection of foundation pit support,it has the advantages of large lateral stiffness,can effectively limit lateral deformation and so on,and can be used for supporting deep foundation pit,however,there are few doublerow piles in the round gravel stratum,and the related mechanism still needs to be studied.In this paper,based on the deformation and stress characteristics of doublerow piles in the deep foundation pit of Nahong Interchange Station of Nanning Metro Line 4 in the round gravel area,the following works are accomplished:(1)According to the present research situation of double-row pile supporting structure,the calculation model and method of double-row pile supporting system proposed by predecessors are summarized,the advantages,disadvantages and applicability of these methods are analyzed.(2)Based on the method of interaction of front and back row piles,the internal force and horizontal displacement of double row piles in the foundation pit are calculated by Winkler elastic foundation beam and an improved earth pressure calculation model,the displacement and bending moment at each point of the pile body of the front and back row piles are obtained,and the rationality is evaluated by comparing the calculated results with the actual monitoring data.(3)In the aspect of numerical simulation,the corresponding pile-soil interaction model is established by using the ABAQUS general finite element software,and the internal force and displacement deformation of double-row piles are simulated,the applicability of the finite element model is verified.At the same time,the reasonable values of diameter and embedded depth of double-row piles under different design parameters are as follows: 1/13 depth of pile diameter and 1.0 ～ 1.1 depth of embedded depth It is concluded that the effect of passive Earth pressure zone is better for doublerow piles,and the effect of adjusting the spacing of row piles is not obvious.(4)Through the above research work,the comparison of the results of theoretical calculation and numerical simulation with on-site monitoring shows that the numerical simulation has higher reliability for the project.The achievements and problems of this research are summarized,and the future research is prospected.