Investigation Of Spatial Deformation Characteristics And Environmental Effects Due To Deep Excavation In Soft Soil Area

With the growing demand for underground space,large-scale and deep excavation are becoming more and more common.At the same time,the surrounding environment of the excavations in the urban area is complex,and the deformation control requirements are strict.It is of great significance to study the deformation characteristic of excavations,the influence on adjacent buildings(structures)and the deformation control measures,especially in the soft soil area.This study focuses on wall/pile-retained excavations in soft soils.Fisrtly,the mechanical properties of typical soft clay in Zhejiang Province are analyzed through laboratory and field tests.Through the field data analysis,analytical calculation and finite element simulation,the spatial deformation characteristics of the excavation and the influence on adjacent buildings(structures)are analyzed.The main work and results are as follows:(1)The simplified method for HS model parameter selection of four typical soft clays in Hangzhou area is proposed by laboratory test and back analysis.Combined with the field test in Zhejiang,calculation method for the small strain parameters G0 is proposed according to soil type and soil depth.(2)In the saturated soft clay area of Hangzhou,the multi-propped excavation with flexible support shows significant spatial effect in both lateral displacement and surface settlement.Combined with the field data analysis,a modified prediction method for distributions of deformation parallel to the excavations is proposed;the spatial deformation characteristics of narrow and long subway excavations are analyzed.(3)By performing FEM orthogonal test,it is founded that the length and depth of excavation have significant influence on the PSR(plane strain ratio).The PSR value will remains above 0.9 after the length reaches 5 times of the depth;the ratio between the deformation near the corner and middle-span is mostly affected by the length of the excavation,the stiffness of the sidewall and the excavation sequence.(4)The field data analysis shows that the partition walls have a significant inhibitory effect on deformation.By 3D-FEM parameter study,the selection suggestion of important parameters such as the partition wall height,depth,stiffness and spacing is proposed.Through the theoretical analysis and finite element simulation of T-shaped diaphragm wall,the optimal value range of T-wall length,thickness,depth and spacing is proposed.(5)An analytic method for the deformation response of underlying tunnel affected by excavation is proposed by considering the effects of sidewall unloading,soil shearing effect and depth of the tunnel.The accuracy of the method is verified by comparing with field data and 3D finite element simulation results,and the method is compared with the Winkler elastic foundation beam calculation model.(6)Field data analysis and 3D-FEM simulation are carried out for a twin-tunnel adjacent to a large excavation in the north of Hangzhou.The results show that the tunnel had a large settlement even if the tunnel vault is below the excavation base.The finite element simulation results show that both the isolation piles and partition walls can well restrict the tunnel deformation;the "traction" effect of horizontal displacement was not observed since the soil reinforcement between the retaining wall and the isolation pile.