DEM Investigations on the Mechanism of Earth Pressure Balanced Shielding Through Nonuniform Soils

The increasing scarcity of urban spatial resources has led to the growing development of urban subways. The earth pressure balanced (EPB) shield machine has become one of the main tunnel boring machines in metro tunnel construction due to its economic efficiency and versatility. In this study, the spatial heterogeneity of soil properties in the shield tunnel stratum is considered, and the three‐dimensional (3D) random discrete element method (RDEM) is applied to investigate the mechanisms of tunnel face instability and ground deformation for EPB shield tunneling in spatially heterogeneous stratum at both macro and microscopic levels. Numerical triaxial tests with a flexible boundary are carried out to establish the relationship between key macro‐microscopic parameters. Based on the RDEM, a shield tunnel model with spatially heterogeneous stratum and EPB shield machine is built and validated. Then, 16 sets of shield tunnel excavation simulations are conducted, including one set with homogeneous stratum and 15 sets with spatially heterogeneous strata. To consider the influence of excavation disturbance, the EPB shield machine keeps moving and the cutterhead keeps rotating in all simulation processes. Results reveal that overlooking spatial heterogeneity in soil properties may underestimate the risks of shield tunnel face instability and ground deformation.