Influenced Zone of Deep Excavation and a Simplified Prediction Method for Adjacent Tunnel Displacement in Thick Soft Soil

Based on the statistics of 42 case histories, 732 finite element numerical simulations are conducted to determine the scope of the influenced zone of deep excavation under different conditions of excavation depth (He) and the maximum retaining wall deflection (δhm). On this basis, the effects of He and δhm on the scope of the influenced zone are studied, and a simplified prediction method for the scope of the influenced zone under any He and δhm conditions and the adjacent tunnel displacement is proposed. Then, the reliability of the proposed method is verified by comparing it with the current research and case histories. And finally, the proposed method is applied to an actual project, and the application effect is evaluated. The results show that the range outside the pit can be divided into “primary”, “secondary”, “general”, and “weak” influenced zones. The influenced zone can be simplified as a right-angled trapezoid shape, and the scope of influence zones can be quickly determined by defining three parameters: width coefficient M, depth coefficients N1 and N2. The parameters M and N2 have a linear relationship with He and δhm, and N1 varies between 1–2 with an average of about 1.5. In actual application, the effect of deep excavation on the adjacent tunnel can be alleviated by using the proposed method to predict the excavation-induced displacement of the adjacent tunnel and take some measures.