Research And Application On Numerical Simulation Method For Shield Tunneling

In urban underground construction, shield tunneling method becomes the first choice because of its safety, rapidity, economy. However there are complex interactions between physical and mechanical factors. Prediction of ground settlements, cutting face stability, safety of ground structures, shield movements, excavation torque is very hard. Besides, relations between tunneling parameters are still unclear.In this paper, the continuous steady-state construction process of shield tunneling is discretized to a step-by-step steady-state process. All relevant construction components and factors have been taken into account. A finite element method for simulating shield tunneling process is proposed. In this method, the steady-state characteristic in macro aspect and dynamic characteristic in local aspect are taken into consideration. The potential engineering value of the proposed method is demonstrated by application in large scale shield tunneling project.In shield tunneling, most research work focus on the important macro-properties. Based on the integrity assumption of shield-soil-structure system, a 3D finite element model for shield tunneling is established. In this model, the impact of shield structure, operation parameters and environmental factors on shield tunneling are taken into account besides construction factors. After that, numerical simulation method for simulating shield machine's steady-state advancing process is introduced. It is further employed in Nanjing Yangtze River tunnel project to predict ground settlements, flood levee settlements, cutting face stability and shield movements. Investigation on the effects of shield weight distribution, the taper of shield skin, the propelling forces and their distribution, the over-cut of cutterhead, the weight and stiffness of flood levee extends applications in shield machine selection, shield structure design, construction parameter match and safety prediction of environmental structure etc.Besides macro-properties, local-properties, especially the dynamic interactions in soil-cutting process in shield tunneling influence the cutterhead performance and cutting face stability dramatically. In order to investigate dynamic interaction between soil and cutterhead, a 3D dynamic numerical approach for simulating the soil excavation process is proposed. In this approach, large deformation in soil is handled; Soil failures and flows are captured. Methods for reducing the model size, initializing the soil stress and deciding the mesh refinement of this multi-scale soil excavation problem are introduced. Numerical simulation of soil excavation process in a large scale model test for slurry shield tunneling is carried out to validate the proposed approach. Dynamic response of cutterhead is obtained. The effect of mesh refinement on results is analyzed. According to the parametric study of cutterhead-soil interaction, relations between cutting torque, velocity, acceleration and soil properties have been derived. The findings of this work can provide a reference for cutterhead selection and design.Studies show that soil stress state is disturbed during shield tunneling. This disturbed soil stress state causes ground settlements, and besides, it impacts cutterhead excavation performance and cutting face stability. Therefore, a joint numerical method for simulating the steady-state process of shield tunneling in macro aspect and dynamic interaction of soil excavation in local aspect is proposed. In this method, the disturbed soil stress is the boundary condition for cutting stability analysis and cutterhead-soil interaction simulation. Submodeling method is used to coordinate different mesh refinements and control the precision in transferring disturbed soil stress. Validation of this joint numerical method is made by numerical simulation of shield tunneling process in Shanghai Chongming Yangtze River tunnel project. Results show the disturbed soil stress and the development curve of cutterhead excavation torque which can provide a reference for cutterhead adaptability investigation and operation parameters control.In order to reduce the large computational effort in shield tunneling simulation, investigation on parallel computing efficiency is carried out. It is noticed that: on SMP parallel platform, iterative methods are faster than direct method and the impact of frictional contact between shield skin and soil on direct method is greater than iterative methods; on DMP parallel platform, the increase in CPU number doesn't always cause decrease in computing time as to DPCG solver; when 12 CPU are used, the least computing time can be achieved. Based on the research of parallel computing efficiency of cutterhead-soil dynamic interaction simulation, it is found that: ALE element processing dominates the total computing time; the cube shaped subdomains decomposed by RCB method exhibits the best parallel computing efficiency.