Numerical Study on the Collapse Behaviors of Shallow Tunnel Faces under Open-Face Excavation Condition Using Mesh-Free Method

The stability and deformation of shallow tunnel faces are hard to predict, and the associated failure mechanisms are also indistinct to date. In this work, we incorporate the softening function and strain-dependent dilation model into a smoothed particle hydrodynamics (SPH) framework to simulate the collapse behaviors of shallow tunnel faces in cohesive–frictional soils under the open-face excavation condition. To this end, the stratum is modeled as a cohesive–frictional soil described by the elastoplastic constitutive model in combination with the Drucker–Prager yield criterion. Softening and strain-dependent dilation behaviors of soils are described by the softening function and the dilation model, which are incorporated into the constitutive model in the framework of the SPH method. For the deformation analysis, the effects of the cover depth variation on face extrusion and ground surface subsidence are investigated. For the face stability analysis, the impacts of the cohesion and the internal friction angle of surrounding soils on the safety factor of shallow tunnel faces are highlighted. Then, comparison is made between the results obtained from the present SPH method and those given by the finite-element method (FEM) and existing centrifuge model tests to verify the proposed SPH procedure. Ultimately, the main outcomes of the current work, including deformation features and safety factors of shallow tunnel faces, are presented.