Study On Long-term Settlement Crossed By Shield Tunneling In Water-rich Soft Soil

The settlement induced by excavation in subway tunnel constructing by shield contains construction settlement and long-term consolidation settlement. It is very important in the construction of shield tunnel to forecast and control the construction settlement and long-term consolidation settlement. Combining with shield tunneling practice of Suzhou No.2subway, a study on the behavior and control of the long-term settlement induced by tunneling in the special stratum of water-rich soft soil was made through field measuring and testing, theory prediction and numerical simulation.(1) The effect of the settlement during tunneling, backfill grouting, soil properties on long-term settlement was studied based on the measured data, and the long-term settlement development law was summarized. The long-term ground settlement is positive correlated with the settlement during tunneling. Long-term ground settlement would be obviously reduced by backfill grouting. Impact on the long-term settlement of clay is larger than sand, With the90～160days consolidation settlement development, the tilt rate of major buildings has an increasement of0.03‰～0.6‰.(2) A theory prediction about the long-term ground settlement was made and we got the value of the ultimate settlement and the time to get there. When comparing the measured data with forecast data, the result shows that they are consistent with each other, and settlement during tunneling accounts for about40%of the total settlement. The ground settlement will be basically stable about1year and ultimate settlement will be stable after3years.(3) Based on the3D numerical simulation, the character and its influencing factors of the long-term consolidation settlement of shield tunneling in water-rich soft soil is studied. The result shows that long-term ground settlement also accords with Gaussian Curve, and the settlement trough of clay widens and deepens with time due to consolidation process. More span times are needed for surface settlement to stabilize when permeability coefficient becomes smaller, but it seems the surface settlement due to consolidation varies little when permeability coefficient becomes smaller.