Study on the excavation disturbed zone during tunneling in sandy cobble stratum considering the material meso-structure

Abstract The excavation disturbed zone plays an important role in the evaluation of tunnel stability. The identification of the excavation disturbed zone is perceived as a main concern. Taking the material meso-structure into account, this paper investigates the construction mechanical behavior in heterogeneous sand cobble stratum and aims to precisely predict the excavation disturbed zone. Firstly, the meso-scale numerical models were used to simulate tunnel excavation in sandy cobble strata, in which the large-sized rock blocks and fine-grained soil matrix were treated as separate constituents. Then, the stress redistribution and deformation performance in the ground during tunneling were explored in detail. Subsequently, combined with the deformation performance characteristics, a method for identifying the excavation disturbed zone was proposed. The boundary of the excavation disturbed zone can be identified by the displacement mutation point of the monitoring paths. Finally, a parametric study was performed to understand the influence of key factors on the excavation disturbed zone, including the rock meso-structure parameters, the soil matrix properties, and the tunnel geometry characteristics. The simulation results indicate that both the rock content and rock size have a significant impact on the excavation disturbed zone, the strength parameters and lateral pressure coefficient have a marked effect, and the tunnel radius and tunnel burial depth have a negligible influence on the excavation disturbed zone under the given conditions when normalized.