Abstract

Despite plenty of research studies in design of segmental tunnel lining, there have still been serious concerns in damage mechanism of segmental lining in weak rock masses. With significant increasing of mechanized tunnelling practically in all kind of ground, including highly weathered rocks, severely jointed rocks, shear, and fault zones, squeezing, and swelling prone conditions, the need to investigate the mechanical behaviour and the damage mechanism of segmental tunnel lining is unavoidable. Any misjudging of those adverse geo-conditions may often cause an irreversible economical loss in the tunnelling project. This paper deals with the significant design aspects of segmental lining for such difficult rock mass conditions which can cause lining deformation and failure in segment in terms of either compression or tension as well as in the segment joints. Further, some critical design aspects extracted from the tunnel T26 of Ankara – Eskisehir high speed railway are presented and analysed.

Introduction

With increasing mechanized tunnelling in wide range of ground qualities from soft soils to poor rocks, medium to highly jointed rock masses, the geological and geotechnical uncertainties are being amplified due to the lack of sufficient ground investigation which in most cases is unavoidable for many economic reasons and technical limits. Unfortunately, it might be too late when one of the involving parties in project such as owner, contractor, and designer recognizes a remarkable unforeseeable condition and inconsistency because both machine and lining have already been suited for the project.

Therefore, identifying and quantifying the main sources of risk in terms of geo-hazards is crucial to minimize the possible impact on machine drive and segmental tunnel lining.

In this paper, an effort is made to study the modes of segment damage due to overstressing as a consequence of prevailing adverse geo-hazards, focusing on some significant design aspects. Broadly speaking, the tunnel segments shall support appropriately all type of acting loads while crossing the difficult ground, achieving Ultimate Limit State (ULS) verification and guarantying both short and long-term stability of the tunnel. Any types of segment overloading bring about the failure and the damage in concrete segment. Some typical damages in segmental tunnel lining, resulting from geo-risks in difficult rock conditions are represented in Figure 1.

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