MESOSCALE NUMERICAL STUDY ON THE TUNNELING-INDUCED GROUND RESPONSE IN A SANDY COBBLE STRATUM CONSIDERING THE ROCK ORIENTATION ANGLE

In engineering practice, oval or subcircular pebbles are distributed in ground at different orientation angles. It investigates the effect of the rock orientation angle on the ground response during tunneling in sandy cobble stratums, with special attention to the material meso-structure. By treating the ground material as a composite of rock blocks and soil matrix, mesoscale numerical models were established. A series of simulations were carried out to model the tunnel excavation using the mesoscale models. By comparing the ground stress between the simulation results and the theoretical values, the applicability of the mesoscale models was verified. Based on this, the ground response during tunnelling in a sandy cobble stratum is analyzed from the viewpoint of stress distribution and deformation performance. The simulation results show that, with the increase of the orientation angle from 0° to 90°, both the shape and extension of the plastic zone changes, and the vertical stress in the soil mass at the tunnel side increases gradually. Under given conditions, the maximum surface subsidence increases linearly with the increase of the rock orientation angle at a relative rate of 5.17% per 10°. The width coefficient of the surface settlement trough first increases and then decreases. When the rock orientation angle is 30°, the width coefficient of the surface settlement trough reaches the maximum value. The relationship between the maximum subsidence S_max(z) with the depth z can be described by a power function. The relationship between the width coefficient of the subsurface settlement trough i(z) with the depth z can also be described by a power function.