Abstract: To investigate large deformations, such as ground settlement due to tunnel excavation instability, a Drucker-Prager elastoplastic constitutive model incorporating a dynamic friction coefficient is developed and integrated into the smoothed particle hydrodynamics (SPH) framework. The proposed theoretical framework is validated via silo flow and tunnel collapse tests. In the silo flow experiments, a distinct inverted triangular region is observed in the flow through particle image velocimetry technology. Further, the SPH simulation reveals the strain and stress field distribution. Subsequently, an SPH analysis model for tunnel collapse is established based on real engineering scenarios to examine the effects of the static friction coefficient and burial depth ratio on the runout distance of collapsed materials and the range of surface settlement. The findings are as follows: (1) The runout distance of the excavated material increases as static friction coefficient decreases, with reduced intersoil frictional resistance enhancing susceptibility to soil displacement and reducing tunnel excavation interface stability. (2) With decreasing static friction coefficient, the soil experiences a pronounced release of stresses during tunnel excavation, substantially increasing the width and depth of the surface settlement trough. (3) The tunnel cover-to-diameter ratio significantly affects the shape of the settlement trough but has minimal influence on the runout distance of excavated material. (4) With increasing tunnel cover-to-diameter ratio, the surface settlement trough becomes more developed and symmetrical.

Key words: tunnel face instability, ground subsidence, smoothed particle hydrodynamics, silo flow, large deformation, friction coefficient relation