A Numerical Study on the Rock Breakage Mechanism with TBM Disk Cutter in Calcareous Cemented Sand Pebble Stratum Using a Coupled FEM-DEM Method

The calcareous cemented sand pebble stratum is a very poorly adapted stratum with the characteristics of high pebble strength, unstable mechanical properties and strong dispersion. In order to study the rock-breaking mechanism of disk cutter in calcareous cemented sand pebble stratum, a 2D cemented sand pebble model was established using random pebble generation procedure according to the distribution characteristics of the calcareous cemented sand pebble stratum of Lanzhou Metro Line 1. The parameters of the cemented sand pebble model were calibrated using numerical Uniaxial compression and Brazilian tests. The rock-breaking mechanism at different penetration depths, cutter spacings and penetration speeds was analyzed using the coupled finite element and discrete element methods (FEM-DEM). The results showed that the cutter breaks the rock mainly through the crushing area to transfer the load between the pebbles by point to point in the stratum. When the transfer load is greater than the ultimate strength of the pebbles, then the pebbles are broken due to the shear–tension mixing damage. The pebble fragmentation area and breakage energy consumption both increased linearly with increasing penetration depth, but the specific energy increased first, then decreased and tended to be stable finally. As the cutter spacing increased, the pebble fragmentation area and rock breakage energy consumption were decreased and then increased while the specific energy increased first and then decreased, and the outer profile of crushing area was distributed in "n" type. However, as the penetration speed increased, the pebble fragmentation area and specific energy decreased and increased with different power functions, respectively.