Interaction Mechanism And Deformation Control Of Foundation Pit And Tunnel In Lacustrine Soft Soil Area

Based on the case study of the deep and large foundation pit adjacent to the lacustrine soft soil area of the Hangzhou Metro Line 1 between Cheng and Hu,the theoretical derivation,case statistics comparison,numerical simulation and model test are carried out to study the stress and deformation laws of the adjacent tunnels during excavation.The main contents are as follows.?1?Considering the uneven distribution of foundation parameters along the longitudinal direction of the tunnel and the disturbance of the excavation of the foundation pit,based on the Mindlin basic solution to evaluate the change of the additional load on the adjacent lining of the excavation of the foundation pit.Vlazov foundation lining model is put forward,which is affected by the ratio of pit to tunnel.By comparing and analyzing the actual monitoring data,the application scope of the analytical formula and the applicability of the foundation coefficient of the enclosure are discriminated and analyzed.?2?Based on 3D finite element ABAQUS,the author verified some parameters of the above analytical model.The comparative analysis of monitoring data and simulation results shows that when the trend and law of numerical simulation are consistent with the field measured deformation data,the surrounding pressure of lining corresponding to layered excavation and support of foundation pit presents a bell-shaped distribution,which corresponds to the analytical solution of additional load.In view of the large lateral displacement of the lining of the project,taking the thickness of the foundation pit floor,the size of the reinforced concrete transverse support,the location of the support,the thickness and depth of the diaphragm wall as the parameter variables,taking the structural deformation in all directions as the assessment index,the L₄₉?7⁸?orthogonal table is designed,and the numerical simulation orthogonal test is carried out,and the numerical test results of each engineering example are obtained through comparative calculation.By means of range analysis and fuzzy comprehensive evaluation,the importance order and parameter optimization suggestion of each parameter variable in the analysis example are given.Compared with the measured value,the optimized support form is adopted in this case.The vertical maximum deformation value of the tunnel is reduced to 1.96mm and the horizontal maximum deformation value is reduced to 4.94mm.?3?A model test with a geometric similarity ratio of 1:40 is designed.Based on PIV technology,the variation law of adjacent lining and surrounding strata during foundation pit excavation is monitored and analyzed under the 3D model test condition with or without pre-supporting plates.The results show that the deformation of the pre support plate and the settlement curve of the surface outside the pit obtained from the model test and the numerical simulation are in good agreement,and the influence of the excavation of the foundation pit on the adjacent tu nnel can be reduced by setting the support plate between the foundation pit and the tunnel.In this paper,the influence of foundation pit excavation on adjacent tunnel in lake soft soil area is analyzed by theoretical method.The numerical experimental design method for the optimization of the supporting parameters of the foundation pit is discussed and the model test for controlling the deformation of the adjacent tunnel is carried out.It provides a comparative reference for the deformation control of the adjacent subway construction in the future.