Study On Safe Spacing And Mutual Influence Of Adjacent Deep Foundation Pits During Crossconstruction

With the rapid advancement of urbanization in China,the exploitation of urban underground space has been greatly developed.In the process of advancement,the foundation pit project has played an important role.In large-scale complex projects such as the development of new towns,the transformation of old cities,and the overall development of subway tracks and surrounding infrastructure.There have been a large number of projects for the simultaneous or cross construction of foundation adjacent pits.The mutual influence between the adjacent foundation pits has greatly increased the safety risk of the large-scale pits,which has become one of the hot issues of concern in the project.It is of great significance for the design and construction of foundation pits to explore the spacing that does not affect the excavations and the deformation force characteristics of the adjacent excavations when the spacing is small.Therefore,the following work was mainly carried out in this paper in order to study the deformation characteristics of the cross construction of adjacent foundation pits:1.A calculation model for soil pressure in the limited soil between two adjacent foundation pits was established.The calculation expressions of the fracture angle and the earth pressure of the limited soil are given respectively with considering the influence of the axial force or not.After that,the change law of the fracture angle and the distribution characteristics of earth pressure are analyzed.The safe spacing of adjacent foundation pits are defined and given.2.The characteristics of stress and deformation of excavation were analyzed,PLAXIS finite element software and HSS soil constitutive model were selected to establish a two-dimensional numerical model.Numerical analysis of different spacing between the two adjacent excavations was carried out and the recommended safe spacing value was given.The stress and deformation characteristics of the adjacent foundation pits were analyzed within a safe spacing during the cross construction.Including the horizontal displacement of the adjacent and non-adjacent sides of the retaining wall,the supporting axial force,the ground surface settlement outside the excavation,the bottom of the pit uplift and the earth pressure of the retaining wall.We have clarified the mutual influence of cross construction of adjacent foundation pits.3.Using finite element numerical simulation,the control measures for the mutual influence of adjacent foundation pits were discussed from four aspects: reasonably arranging the construction sequence,changing the design parameters of the retaining structure,optimum support arrangement and pit unloading and additional bracing.4.Combined with the actual engineering data of adjacent foundation pits,the analysis of monitoring data changes in horizontal support axial forces,deep soil lateral displacements,and ground surface settlements outside pits were analyzed during the crossconstruction process.The rationality of the theoretical analysis and numerical simulation analysis of this paper was verified.