Geomechanical Behavior of a Damaged Circular Tunnel in Anisotropic Rock Subjected to Fire Loads, Considering Excavation Damage Zone (EDZ)

Jake McCarey and Lucas Tara

Comparison of excavation induced damage between a tunnel constructed by drill and blast (DB) and a tunnel constructed using a Tunnel Boring Machine (TBM).

Comparison of excavation induced damage between a tunnel constructed by drill and blast (DB) and a tunnel constructed using a Tunnel Boring Machine (TBM)

Undergraduate Student Project

Introduction

In our fast paced life, we tend to take for granted the built infrastructure around us that makes our daily activities possible; Tunnels are no exception. When driving through a tunnel, we don't think anything of what lies beyond the concrete liner that makes passing through the tunnel possible. While motorists see a smooth concrete liner, the rock directly beyond the liner is fractured and damaged both naturally as well as due to the tunnel excavation process. My name is Jake McCarey. I'm a senior Civil Engineering major at the University at Buffalo. Myself and my colleague, Lucas Tara, conducted research on the geomechanical behavior of damaged tunnels under Dr. Kamelia Atefi-Monfared. Since this past fall, myself and Lucas worked on developing a finite difference based numerical model to determine the behavior of tunnels that have been damaged during the excavation process, and are now subjected to hazard scenarios such as tunnel fire. Our research seeks to understand - for the first time -response of a damaged tunnel in hard rock, subjected to different hazards in order to ensure long-term stability of the tunnel structure.

Abstract

This paper is aimed at understanding the interactions between tunnel and the excavated damage zone (EDZ) under multiple hazard scenarios. The evolution of EDZ caused by different tunneling methods has been previously widely researched through physical and numerical modeling. One main focus of previous studies has been on quantifying stresses and deformations in shallow tunnels in soft soils under various hazard loading scenarios. There is currently no comprehensive model that considers the geomechanical behavior of an already damaged tunnel under hazard loads. More specifically, the impact of key parameters including situ stress regime, transient unloading subsequent to excavation; and existence of anisotropic fracture networks and features such as faults/folds - typical in hard rocks - has not been assessed. The overarching goal of this study is to quantitatively determine the post-excavation response of a damaged lined tunnel in an anisotropic rock medium subjected to different hazards. A rigorous finite difference based numerical model is developed and validated in our study, to replicate a tunnel embedded in a wide range of geological condition - relatively intact, massive, and hard rock - subjected to high global initial in situ stresses. Various scenarios for fracture network is introduced surrounding the tunnel, representing damage. The simulated tunnel is then subjected to various  tunnel fire scenarios, to evaluate the geomechanical response and stability.

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