| Nowadays,with the accelerating development of urban underground space,especially in the coastal areas economy is highly developed,it inevitably brings about the problem of the impact of foundation pit dewatering and excavation on existing underground structures.The Yangtze River Fifth Bridge Jiangnan shield receiving well has a depth of 40m.It is closed to the Yangtze River and adjacent to the existing Qingao tunnel complex.The groundwater level is high,the deformation control requirements are strict,and the construction conditions are extremely complicated.Therefore,the study of the impact of the deep foundation pit dewatering and excavation on existing tunnels is very nesscery.In this paper,numerical simulation and field monitoring data are used to simulate and predict the whole process of Jiangnan working well construction,and the deformation and stress laws of existing tunnels under different precipitation conditions are analyzed.The main work and achievements are as follows:(1)The research status of the deformation of the foundation pit and the existing tunnel during the dewatering and excavation process of the foundation pit were summarized,and the control standards of the existing tunnel deformation were also concluded.(2)The geological conditions of the foundation pit of Jiangnan working well were analyzed,and the reverse construction method was introduced in detail in combination with the site investigation.(3)The finite element software ABAQUS were used to establish the generalized model,and the deformation and stress of the tunnel under different dewatering depth and water-cut curtain insertion depth were calculated.Several rules were revealed as follows.Firstly,the impact of dewatering on the surrounding environment can be divided into strong,middle and weak influence area.In the affected area,the dividing line is in the form of a double-fold line around the bottom of the continuous wall.Secondly,the horizontal displacement of the tunnel caused by dewatering moves to the inner side of the foundation pit.The displacement of tunnel is approximately linearly reduced from top to the buttom.The increase of the insertion depth of the water-cut curtain can reduce the horizontal displacement of the tunnel.Thirdly,dewatering mainly causes tunnel settlement,the settlement range is approximately linear decreasing from the side of the tunnel near the foundation pit to the distal end.And the increase of the insection depth of the water curtain can effectively reduce the tunnel settlement value.(4)FLAC~3DD were used to establish a three dimensional finite element analysis model of working well,existing interval tunnel structure and stratum.Firstly,the inversion scheme was drawn up.The weights of each parameter were numerically calculated.The elastic modulus,cohesion and friction angle of the soil were selected as suitable inversion parameters.Then the six-stage layered excavation process is carried out according to the measured data.The parameter inversion was carried out,and the deformation of the retaining structure and the adjacent tunnel was predicted in stages,which effectively guided the construction and ensured the safety of the tunnel structure. |
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