Research On The Deformation Law Of Deep Metro Foundation Pit In A Eastern Chinese City

In recent years with the development of the economy,the development and utilization of underground speace become imperative.As population increased and traffic congested, underground railway become a one of important method to slove traffic jam.In metro construction,the most important part is the deep foundation pit of subway station,it is always attached much significance to its complex construction difficult construction and high requirement safety,so the study on deformation of metro foundation pit construction becomes particularly important.This article based on the metro deep foundation pit engineering of the city in east of China,by analysising field observation datasets,building deformation prediction particle swarm optimization BP neural network of deep foundation pit and using 3-Dimension numerical simulation analysis to sum up regularity of the metro deep foundation pit engineering during excavation,the regularity can provide reference for the design and construction of the metro deep foundation pit engineering in this region.The main work and research result are as follows:(1) Combined with the results of numerical simulation analysis and field observation datasets summed up the laws of deformation in the process of foundation pit excavation, the laws include the changes of ground surface settlement,pile body lateral displacement and axial force.(2) Through field observation datasets,the deformation prediction particle swarm optimization BP neural network of deep foundation pit has been built,it can be used for predicting the settlement of surrounding buildings and ground in the process of foundation pit excavation.(3) Settlement of foundation pit surface change showing the certain regularity in the process of foundation pit excavation, along the edge of the pit in different positions, the ground surface settlement showing the groove type change, the maximum settlement of surface do not occurre at the edge of the pit but keep some distance from the edge of the pit.(4) Lateral displacement of Retaining pile increases with the depth of excavation, until the completion of the excavation deformation of pile stabilized.In the process of foundation pit excavation,the maximum lateral displacement value always took place in a certain position in the middle part of the pile body but the displacement of the two ends of pile are very small, the displacement appear a parabolic deformation. This phenomenon indicates that the Concrete support and the argillaceous siltstone of partial fixing play an important role to limit displacement of pile end on both sides.(5) Using the deformation prediction particle swarm optimization BP neural network for predicting the settlement of surrounding buildings,underground pipelines and ground in the process of foundation pit excavation, the development trend that the short term related to deformation can be obtained,this prediction algorithm has a better forecasting accuracy and higher credibility.(6) The axial force of support system showed certain regularity in the process of foundation pit excavation, both the axial force of Concrete support or steel support always after a slow increasing process finally will be stable.(7) Through the results of numerical simulation analysis and field observation datasets indicated that the deformation is relatively small in the process of foundation pit excavation, the supporting system has high security, there is surplus corresponding safety coefficient to be use for parametric optimization design to save the project construction cost.