Numerical investigation of the convex effect on the behavior of crossing excavations

A 3D numerical model considering the soil-structure interaction is presented in this paper to examine the ground movement and internal force during the construction of Qingdao North Metro Station, China with a special focus on the convex effect of the crossing excavation. The influence of intersection angles and soil resilience characteristics on deformation behavior is discussed, and the suitability of two alternative constitutive models applied in excavation simulation is also considered. The analysis results show that a notable convex effect appears to be associated with the crossing excavation, and the intersection is the key area requiring special attention. The displacements at the comer decrease with increasing crossing angles. The axial loads of struts along the retaining pile wall are unequal, and the values near the cross section are generally larger than the average loads of the left-sided ones. The modified Cam-Clay （MCC） model, which is capable of describing the loading-unloading criterion and identifying the stiffness difference of strain hardening between loading and unloading, can yield a relatively high accuracy of estimation for the behavior of excavations in comparison to the Mohr-Coulomb （MC） model. Furthermore, slight soil deformation resilience after unloading can reduce the ground surface settlement and enhance the ground stability.

Interaction analyses between tunnel and landslide in mountain area

This paper focuses on the analytical derivation and the numerical simulation analyses to predict the interaction influences between a landslide and a new tunnel in mountain areas. Based on the slip-line theory, the disturbance range induced by tunneling and the minimum safe distance between the tunnel vault and the sliding belt are obtained in consideration of the mechanical analyses of relaxed rocks over the tunnel opening. The influence factors for the minimum safe crossing distance are conducted,including the tunnel radius, the friction angle of surrounding rocks, the inclination angle of sliding belt,and the friction coefficient of surrounding rocks. Secondly, taking account of the compressive zone and relaxed rocks caused by tunneling, the Sarma method is employed to calculate the safety factor of landslide. Finally, the analytical solutions for interaction between the tunnel and the landslide are compared with a series of numerical simulations, considering the cases for different perpendicular distances between the tunnel vault and the sliding belt. Resultsshow that the distance between the tunnel vault and the slip zone has significant influence on the rock stress and strain. For the case of the minimum crossing distance, a plastic zone in the landslide traversed by tunneling would be formed with rather large range, which seriously threatens the stability of landslide. This work demonstrates that the minimum safe crossing distance obtained from numerical simulation is in a good agreement with that calculated by the proposed analytical solutions.