Work

Mechanical behavior of tunnel excavation at great depth in coarse-grained soil-rock backfills: Insights from FDM-DEM simulations

Year: 2025

Type: article

Abstract: Tunneling through deep backfills composed of coarse-grained soil-rock mixture (SRM) poses critical engineering challenges due to their loose structure, high porosity, and large block inclusions. These deep, fractured, and highly heterogeneous fill materials exhibit complex mechanical responses, making traditional design and predictive methods insufficient. This study employs a coupled finite difference method-discrete element method (FDM-DEM) framework to investigate excavation-induced deformation and stability in deep SRM backfills. Parametric simulations quantify the effects of excavation method, burial depth, tunnel diameter, and rock block content on ground response. The study also examined the role of pipe roof support parameters, including diameter, spacing, and installation angle, in mitigating deformation and fracture propagation. Results demonstrate that the reserved core soil method (RCSM) provides enhanced stability, reducing the ultimate crown collapse by up to 0.28 m compared with the full-face method and promoting a more uniform redistribution of stress. Increasing burial depth leads to larger displacements and a transition in failure mode from basal shear to crown-dominated collapse. Higher rock block content enhances interlocking and overall stiffness while shifting deformation toward the sidewalls. Systematic optimization of the pipe roof support shows that a configuration with a 127 mm diameter, 400 mm spacing, and a 5° installation angle provides the best overall performance, reducing surface settlement by up to 41.5%, limiting grout-body cracking, and improving control of shear concentration at the vault-shoulder interface. These findings provide a quantitative and mechanism-based framework for tunnel support optimization in coarse-grained SRM deep backfills. The coupled FDM-DEM approach not only captures the multi-scale mechanical response of SRM but also bridges the gap between advanced numerical methods and empirical engineering design, thereby enhancing stability and reducing construction risks.

Source: Rock Mechanics Bulletin

DOI: 10.1016/j.rockmb.2025.100281

Authors: Yuhao Gao, Zhongping Yang, Shiqi Li, Xinrong Liu, Gonggu Xiang, Wenjie Xu

Institutions: Chongqing University, State Key Laboratory of Coal Mine Disaster Dynamics and Control, Kunming University of Science and Technology, Tsinghua University

Language: English

Topic: Geotechnical Engineering and Analysis

Subfield: Safety, Risk, Reliability and Quality

Field: Engineering

Domain: Physical Sciences

SDG: Industry, innovation and infrastructure

Open Access status: diamond

Funders: Ministry of Science and Technology of the People's Republic of China, National Key Research and Development Program of China