Abstract
Deep strata of coarse-grained Soil-Rock Mixture (SRM) are widely distributed in southwestern China, posing a serious threat to construction and operational safety due to their loose structure, high porosity, and abundant rock blocks. Tunnel excavation in such deep-buried, fractured, and highly heterogeneous backfill materials often exhibits complex mechanical responses, rendering conventional design and prediction methods inadequate. In view of this, this study employs a coupled Finite Difference Method and Discrete Element Method (FDM-DEM) framework to systematically investigate the mechanical responses induced by tunnel excavation in SRM. The analysis focuses on the influence of excavation methods (full-face method, bench cut method, and central core method), burial depth, tunnel diameter, and rock content on surrounding rock stability. Additionally, the study evaluates the role of pipe roof support parameters (pipe diameter, spacing, and installation angle) in suppressing deformation and fracture propagation. Results demonstrate that the central core method exerts more significant control over surrounding rock deformation and stress concentration under greater burial depth conditions. Increased burial depth induces a crown-dominated failure mode and significantly increases displacement. Increased rock content can alter the load transfer path, enhancing overall structural stability through strengthened interlocking between particles while simultaneously causing migration of failure locations. Larger tunnel diameter intensifies excavation disturbance, necessitating stronger support measures to ensure crown stability. Furthermore, pipe roof support with large pipe diameter and small spacing helps significantly reduce grout body fracture and improves deformation control capability. Installation angle exhibits a nonlinear influence on support effectiveness: support performance is optimal at moderate inclination angles, while excessive inclination angles tend to induce stress concentration at the junction between crown and side walls. The research findings can provide theoretical support and engineering guidance for optimizing tunnel construction and support design in deep-buried coarse-grained SRM backfill, contributing to improved structural stability and reduced construction risks.
Full Text
Preamble
Title: Mechanical effects of tunnel excavation in deep soil-rock mixed backfills based on a discrete-continuum coupled approach
Authors: GAO Yuhao¹, YANG Zhongping¹,²,³*, XIANG Gonggu¹
Affiliations:
¹School of Civil Engineering, Chongqing University, Chongqing 400045, China
²Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, China
³National Joint Engineering Research Center of Geohazards Prevention in The Reservoir Areas (Chongqing), Chongqing 400045, China
Abstract: Deep soil-rock mixture (SRM) strata composed of coarse particles are widely distributed in southwestern China. Characterized by loose structure, high porosity, and abundant rock blocks, these formations pose significant threats to engineering construction and operational safety. Tunnel excavation within such deep-buried, fractured, and highly heterogeneous backfill materials often exhibits complex mechanical responses that conventional design and prediction methods cannot effectively address.
In light of these challenges, this study employs a coupled finite difference method and discrete element method (FDM-DEM) framework to systematically investigate the mechanical responses induced by tunnel excavation in SRM. The analysis focuses on the influence of excavation methods (full-face method, bench cut method, and core soil retention method), burial depth, tunnel diameter, and rock content on surrounding rock stability. Additionally, the role of pipe roof support parameters (pipe diameter, spacing, and installation angle) in suppressing deformation and fracture propagation is evaluated.
The results demonstrate that the core soil retention excavation method provides superior control over surrounding rock deformation and stress concentration under greater burial depths. Increased burial depth induces a crown-dominated failure mode and substantially increases displacement. Higher rock content alters load transfer paths and enhances overall structural stability through improved interlocking between particles, while simultaneously causing failure locations to migrate. Larger tunnel diameters intensify excavation disturbance, necessitating stronger support measures to ensure crown stability. Furthermore, pipe roof support with larger pipe diameters and smaller spacing significantly reduces grout body fracture and improves deformation control capability. The installation angle exhibits a nonlinear influence on support effectiveness: moderate inclination angles yield optimal support performance, whereas excessive angles tend to induce stress concentration at the crown-side wall junction.
These research findings provide theoretical support and engineering guidance for optimizing tunnel construction and support design in deep-buried coarse-grained SRM backfills, contributing to improved structural stability and reduced construction risks.
Keywords: soil-rock mixture; loose strata; numerical simulation; tunnel excavation; pipe roof support
Corresponding Author: yang-zhp@163.com