Study On Deformation Control And The Influence On Adjacent Tunnels Of Deep Foundation Pit Excavation

With the rapid development of the economy and the increasing urbanization,the construction of urban underground space plays an important role in the social development,meanwhile the deep foundation pit engineering is also emerging in the urban construction.With the increasing depth and scale of foundation pit,the surrounding environment is becoming more and more complex as well as the deformation control of foundation pit engineering is extremely strict.In the construction of foundation pit,not only to ensure the safety and stability of the foundation pit,but also to reduce the impact on surrounding buildings and adjacent subway tunnels.How to control the deformation of the foundation pit has been one of the key issues of the underground engineering.Meanwhile,the foundation pit engineering is used in the city.The influence and protection of the foundation pit excavation on the environment is also an important topic for the experts and scholars to study.In this paper,the deformation control of the excavation and the influence on the adjacent subway tunnel are studied based on the foundation pit project of Hefei Shengli road.The main work and research contents include the following aspects:(1)Deformation mechanism of the foundation pit excavation.The deformation of the retaining structure,the uplift of the bottom of the pit and the settlement of the ground surface are summarized,then the time and space effects of the excavation of the deep foundation pit are also sorted out.Meanwhile,the deformation characteristics and stiffness equivalent model of the shield subway tunnel are studied,as well as the deformation characteristics of the adjacent subway tunnel are analyzed theoretically from two factors of external force and construction.(2)Finite element analysis of the foundation pit excavation.The MIDAS/GTS is used to simulate the foundation pit of Hefei Shengli road of finite element numerical simulation,then a three-dimensional model is established to calculate the horizontal displacement of the retaining structure,the axial force of concrete support,the settlement of the surrounding surface and the deformation of the adjacent subway line 1.Finally,the monitoring data is compared with the simulated results to verify the accuracy of the numerical simulation.The deformation control of the foundation pit engineering is also studied.Three methods are put forward to reduce the deformation of the enclosure structure,at the same time,the validity of the three methods is analyzed by the finite element method.(3)The comprehensive hazard assessment of the foundation pit.The extension evaluation method is applied to the hazard assessment of foundation pit engineering.In view of the weaknes of single assigning weight method,the combined weighting method is used to determine the comprehensive weight of the evaluation index,then the extension evaluation model is established.The rationality of the evaluation method is verified through project example.