Study On Face Stability And Tunneling Parameters Of Shallow Slurry Shield-Driven Tunnel In Permeable Composite Strata

In recent years, slurry shield is more and more widely used in the construction of river-crossing tunnels for urban subway. However, facing the special conditions of complicated geology, high water pressure, shallow buried depth and so on, how to figure out mechanical mechanism of slurry membrane formation process for slurry shield, make sure face stability in water permeable strata, and choose tunneling parameters, etc, which are urgent to be solved at present.In this thesis, the interval tunnel from Qiushui square to Zhongshan west road in Nanchang rail transit line1is taken as engineering background. Relying on The National Key Basic Research Program of China (No.2011CB013802) and The Research Program of China Railway Tunnel Group, the problem that face stability and tunneling parameters of shallow slurry shield-driven tunnel in permeable composite strata was studied by these means of theoretical analysis, numerical simulation, field test and mathematical statistics. The mainly completed research work is as follows:(1) Starting with the formation mechanism of slurry membrane for slurry shield, the mechanical analysis model of slurry membrane formation process was established. The calculation formulae on the growth rate of slurry membrane thickness, the mud filtration rate and filtration loss at the excavation face for slurry shield were derived. Through analyzing its main influence factors, the influence law was obtained, which was about slurry membrane thickness, the mud filtration rate and loss on the excavation face for slurry shield under different parameters.(2) Based on the upper-bound limit analysis theory, the theoretical analysis model on face stability of the shallow shield-driven tunnel in water permeable strata was established. Meanwhile, the calculation formula on the limit support pressure of the shallow shield-driven tunnel in water permeable strata considering seepage was derived. Combined with engineering example, the rationality of theoretical calculation was verified by numerical simulation, and through analyzing main influence factors of the limit support pressure of shield-driven tunnel, the influence law on limit support pressure of shield-driven tunnel under different parameters was obtained.(3) Slurry shield tunneling parameters in composite strata were analyzed by the mean of mathematical statistics. The variation range of slurry shield tunneling parameters under the different strata and its variation law along the longitudinal direction of interval tunnel were obtained, at last the reasonable control range of slurry shield tunneling parameters was given.(4) By multiple regression analysis, the regression mathematical models of shield tunneling speed and cutterhead torque under the different strata were obtained. Comparative analysis of field test data and fitted value, it is concluded that the regression mathematical models were rational and they could be prediction modes of shield tunneling speed and cutterhead torque.