Experiments And Numerical Simulations On Impact Of Shield Tunnel Construction In Loose Geological Environments

ABSTRACT:Shield method is widely promotion and application in the urban subway construction for its intelligence, fast, safe advantages. However, because shield tunnel needs to control so many factors, it is bound to cause disturbances to surrounding soils, which leads to ground long trapped, formation level displacement and so on. To reduce the harms to construction along pipelines and buildings that caused by shield tunnel, it is necessary to research the ground subsidence caused by the construction.Numerical simulation is one of the effective method, the most current numerical simulation that taken by research workers is based on soil loading principle, and more the mohr-coulomb model. But in fact during the shield tunnel construction, it is a unloading process that the soil is disturbed until stable state. With the method of loading modeling, it will be hard to accurately response ground long do real level.In this article, the Beijing metro line 15th shield project under construction is taken for the engineering background. Base on uninstall soil mechanics methods, proportion, compression, reduced triaxial compression test and conventional triaxial compression test are taken to establish the basic physical mechanics indexes of soil mass stress and strain characteristics to research overlying soil of shield tunnel. In order to establish the differences of c (cohesion),(?) (angle of internal friction), E(elastic modulus),κ(elastic expansion line slope) andλ(normal consolidation line slope) in the two kinds of stress path, fitting the test curses of conventional triaxial compression and triaxial compression by M-C model, D-P model and modified cam-clay model of FLAC 3D. In the meantime, take the conventional triaxial compression test and compression test to establish the value of c,(?),E, then establish the material parameters under unload path.According to the interval monitoring program and the project progress choose the suitable monitoring section, modeling shield interval through FLAC3D. Use the two groups of testing parameters, established by fitting the loading and unloading curse, modeling the influences of the ground settlement through M-C, D-P, modified cam-clay model.Then compare the modeling results and Construction site measured data.Simulation results show that:the load simulation method does not consider the differences between loading and unloading paths giving a larger value; The calculated subsidence value that considering the differences between the two paths are consistent with the actual measurement data.