Study On Influence Of Excavation On Adjacent Existing Metro Tunnel

With the development of city construction,the construction of the subway entered into a rapid development period.The role in promoting economic along the line is significant in consideration,so deep foundation pit engineering adjacent existing metro tunnel become more and more.Under such complex conditions,it is necessary to ensure the safety,quality and progress of deep foundation pit construction,but also to control the deformation of the foundation pit and the displacement of the surrounding soil,especially for the purpose of affecting the existing subway tunnel.The main works and achievements are as follows:1)A number of excavation adjacent existing metro tunnel cases are sorted and analyzed.The relative position of foundation pit and tunnel,the excavation method of foundation pit,the foundation pit retaining structure,the reinforcement of soil inside and outside the pit,the measures of drainage are analyzed by using mathematical statistics method.The influences of excavation on the adjacent subway tunnel are summarized,and the model is treated as a system.The above factors are divided into "external factors" and "internal variable factors",as the guiding ideology of new case analysis.2)Data of both the excavation monitoring and the subway monitoring of a project example in Hangzhou are collated for analysis.The tunnel deformation and displacement,foundation pit support structure and the surrounding soil additional deformation caused by the time and space effects of excavation and construction measures are analyzed in detail.Monitoring data of excavation are compared to analyze with that of subway,and the mapping curves of the correlation value and the distance are obtained.The monitoring data of foundation pit are substituted into the fitting formula to estimate and predict the horizontal displacement and vertical displacement of the subway tunnel structure.3)Based on the engineering example and the geotechnical engineering finite element software Plaxis,the three-dimensional and two-dimensional numerical simulation model are established by using the HSS(small strain hardening soil)model.The results of numerical simulation are compared with the engineering monitoring data to verify the rationality and accuracy of the model and parameters.The spatial distribution and time course of tunnel displacement during excavation process,the relationship between the ultimate displacement behavior of tunnel and the relative position of foundation pit and tunnel,and the excavation method of the foundation pit are analyzed.Some optimum proposals and solutions are proposed based on the above studies.4)The excavation method and the inner supporting arrangement are optimized.The results support the rationality of the optimal design.Some certain references are provided for the other similar projects and using three-dimensional numerical simulation to calculate and predict the deformation and displacement of tunnel.