Study Of Ground Surface Settlement Caused By Large Diameter Slurry Shield Tunneling

With a board strata suitability, large diameter slurry shield is especially suitable for long-distance and large cross-section tunnel under high pore water pressure, which makes large diameter slurry shield is the best option for tunnels cross river or sea. Study of large diameter slurry shield tunneling by numerical stimulation can show the development of strata displacement, which has a positive significance for the protection of nearby buildings and underground pipeline tunnel. The method has the characteristics of low cost and high efficiency. With the development of computer performance and numerical simulation software, it will have broad application prospects.This dissertation is based on Nanjing Yangtze River tunnel project. The data of some real-time monitoring of the right line initial segment was analyzed, and the process of tunnel excavation was stimulated based on PLAXIS3D. The conclusions are as follows:The excavation of large diameter slurry shield tunnel is the main factors of the ground surface settlement. Combined with the excavating parameters, moisture content and specific gravity of excavated soil, the calculation of the excavation of dry soil weight is available. This parameter can be used to roughly estimate the average volume of over-excavated soil of super large diameter slurry shield. Although there are some errors, the result still has a certain reference value. The simulation of shield tunneling by transferring stiffness method has a great effect on the calculation results. When the finite element model was established according to the actual size of the shield shell, the errors of ground surface settlement are very large, and the ground surface settlement curves and the measured ground surface settlement curves vary greatly. While the equivalent surface contraction method is used to simulate the over excavation, the ground surface settlement curves are close to the measured curves, and the development of ground surface settlement is close to the measured development, too. This indicates that the super large diameter slurry shield tunneling simulated by equivalent surface contraction method is more reasonable.The hardening soil model in PLAXIS3D, which considering the difference of soil hardening characteristics and the difference between loading and unloading by the use of the three axis load stiffness E50, three axis unloading stiffness Eur and oedometer loading stiffness Eoed, has certain advantages in the simulation of tunnel excavation problems. When the stiffness parameters cannot be obtained, the soil compression modulus in the investigation report can be approximated as E50of and the three stiffness parameters can be assignment according to the ratio of1:1:3. The calculation results for this case is a certain reference value.In the simulation of shield tunneling by transferring stiffness method, compared to the step-by-step excavation stimulation the ground surface settlement of the whole excavation stimulation is obviously small, but the calculated the stress distribution difference is very small.