Stability Analysis of a Tunnel Nearby Folded Strata Using Numerical Modeling
Authors: Ali H. , Shahzaib M. , Emad M. Z. , Waqas M. , Ijaz W. 
Published: August 2024

ABSTRACT:
The stability of underground structures, like mines and tunnels, has always been a major concern in the field of underground space development works. Reliable prediction of tunnel stability is a key challenge for tunnel engineering, especially when drilling in folded rock masses. Folded strata are layers of rock that have been folded and deformed by tectonic forces. This can create complex geological structures that are difficult for tunnel engineers. This research aims to investigate the stability of tunnels through folded strata (anticline, syncline, and fracture zones). Failure Sequence of the tunnel is simulated using finite difference software. The results of the simulations are analyzed to identify potential failure mechanisms and assess their likelihood and consequences. Based on these simulations, innovative techniques (position and number of tunnels) are developed to enhance tunnel stability in the fold-rich region. The results suggest that FDM software can be used to identify potential areas of instability and to design appropriate mitigation measures. This could help to reduce the risk of tunnel collapse and improve the safety of tunnels in areas with folded strata.

1. INTRODUCTION
The stability of subterranean structures within folded rock formations is of paramount importance. As urban populations grow and the tunneling industry expands, the proliferation of new underground structures introduces novel challenges to their stability. Each project presents unique geological and geomechanical complexities, necessitating the development of reliable stability assessment methodologies and simulation techniques. This imperative has long been recognized, with ongoing research efforts aimed at comprehensively understanding the behavior of underlying strata when subjected to various structural interventions. Recent studies by scholars such as (Rama Sastry, 2023), (Li Li, 2023), and (Zhiming Li, 2023) have addressed tunnel stability issues arising from diverse geological features encountered during excavation worldwide. Utilizing laboratory testing and software-based modeling, these researchers have sought to identify and mitigate specific challenges associated with faults, joints, soft rock/sand layers, and other discontinuities. However, a notable research gap persists concerning the study of folded strata in tunnel construction.
Folded strata present a multitude of complications, including localized stress concentration, tunnel alignment deviations, support challenges, and water ingress, culminating in structural failures. Case studies conducted by (Kasser, 2007; Lüthi, 2016; Marti, 2010; McCullough, 2017; Overman, 2013) underscore the significance of folded strata-induced failures in tunnel projects worldwide. Despite efforts to diagnose the root causes of these failures, effective solutions remain elusive. Thus, this research endeavors to address this gap by developing a numerical model simulating hypothetical folded strata configurations along tunnel faces, thereby elucidating failure scenarios and potential remedies.