Assessment of Discontinuities-Induced Overbreak by Tunnel Advancement using Discrete Fracture Network (Case study: Alborz Tunnel, Iran)

HajiMohammadi, Mohammad Amin; Bahaaddini, Mojtaba; Khosravi, Mohammad Hossein; Vandyoosefi, Hassan

doi:10.22044/jme.2025.15465.2966

Document Type : Original Research Paper

Authors

¹ School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran

² School of Mining Engineering, College of Engineering, University of Tehran

³ Department of Mining Engineering, Faculty of Engineering, University of Birjand, Birjand, Iran

⁴ Geotechnical Engineering Department, General Mechanics Co., Tehran, Iran

10.22044/jme.2025.15465.2966

Abstract

Discontinuities are known as a primary factor in instability of tunnels and underground excavations. To prevent potential damage and overbreak by underground advancement, it is essential to provide a model, which considers both the geometrical and mechanical characteristics of discontinuities. Discrete Fracture Network (DFN) is a conceptual model to represent and analyse the complex system of discontinuities within the rock mass. Combined DFN with analytical or numerical methods can be employed as a scientific tool to analyse generated rock blocks, and their stabilities under different loading conditions. This paper aims to investigate the created overbreak by tunnel advancement in the Alborz tunnel located in the Tehran-North freeway in Iran. First, the geometrical characteristics of discontinuities were surveyed by tunnel advancement in 200 meters. Four major joint sets and a bedding plane were identified and their statistical characteristics were measured. The DFN model was generated and its validity was investigated through a comparison against field data. The average volume of generated blocks in the studied area was measured 0.22 m³. The stability of generated blocks around the opening was kinematically evaluated. The volume of formed blocks around tunnel in the DFN model prone to instability due to static or dynamic loads was estimated 2605 m³ while the measured overbreak in field was 2735 m³. The depth of overbreak in DFN model showed a good agreement with field measurements. The results show that DFN model combined with kinematic stability analysis can provide a scientific tool to investigate geological overbreak in underground excavations.

Keywords

Main Subjects

Rock Mechanics

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Assessment of Discontinuities-Induced Overbreak by Tunnel Advancement using Discrete Fracture Network (Case study: Alborz Tunnel, Iran)

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Volume 17, Issue 1January and February 2026Pages 373-389

Volume 17, Issue 1
January and February 2026
Pages 373-389