Problems Encountered during a Railway Tunnel Excavation in Squeezing and Swelling Materials and Possible Engineering Measures: A Case Study from Turkey

Ebu Bekir Aygar,Candan Gokceoglu

doi:10.3390/su12031166

Abstract

The T3 railway tunnel—under construction within the scope of the Bursa-Yenişehir high-speed train project—is located in northwestern Turkey and has a length of 1250 m. The tunnel is being constructed entirely in silty clay/clayey silt, sand, and clay units, and it is designed in accordance with the principles of weak ground tunneling described by the new Austrian tunneling method (NATM). When the tunnel excavations began in 2013, during and after portal excavations, a failure occurred at the entrance of the tunnel; thus, a revision of the support systems became mandatory. While the excavation works proceeded after the revision phase, a collapse occurred again at the tunnel face where the overburden thickness was low. This study presents the mechanisms of the collapse that took place at the portal location and in the middle of the tunnel. The proposed tunnel support systems and their numerical analyses are also discussed, because the case is interesting for the tunnel community and will inform future tunnel construction work. For this reason, the relationship between portal excavation and tunnel excavation stability is described. Consequently, tunnels excavated through weak ground conditions are considered, and the importance of considering the face stability of tunnels in tunneling studies is underlined.

Highlights

Burgeoning population growth requires the construction of more infrastructure, such as buildings, roads, airports, ports, and dams, which, in turn, increases the demand for finding suitable sites or routes to meet these needs [1]
If the tunnels with a low overburden are excavated beneath residential areas, possible deformations and failures during excavation works directly affect the infrastructure and buildings located in the close vicinity
The tunnel ceiling is secured by the umbrella method and the tunnel face is stabilized by shotcrete and fiber rock bolts

Summary

Introduction

Burgeoning population growth requires the construction of more infrastructure, such as buildings, roads, airports, ports, and dams, which, in turn, increases the demand for finding suitable sites or routes to meet these needs [1]. The tunnel ceiling is secured by the umbrella method and the tunnel face is stabilized by shotcrete and fiber rock bolts In such ground conditions, the very short self-standing time of the opening requires the tunnel support systems to be stabilized immediately. When instability problems in weak soils are examined, many factors are found to be influential Some of these are the groundwater conditions, excavation method, the tunnel support systems, and the mechanical properties of the soil units [4]. The main purpose of the present study is to describe the mechanisms of the failures that took place at the portal location and in the middle of the tunnel excavated in weak ground conditions. The tunnel case presented in the study is interesting for the tunnel community, provides serious experience for future tunnel works, and has scientific merit

Background

Project Description

Problems Encountered During Excavations and Support Systems