Abstract

The construction of long distance water conveyance tunnels in western region of China is inevitably confronted with active faults, which is a unique geological structure with complicated formation mechanism and produces significant adverse impacts on engineering structures. Currently, there is no widely recognized countermeasures for tunnels crossing active faults. This paper makes extensive investigations on cases where active faults are involved in tunnel construction and summarizes the basic design parameters. The available countermeasures are then categorized and the most popular design approach to address active faults is identified to be the flexible joints that are installed on the lining structures at a regular interval. In order to evaluated the adaptability of countermeasures, a numerical procedure is proposed regarding constitutive model establishing, material damage variation approximation, and numerical realization. The proposed procedure is then applied to a water conveyance tunnel in western China. The whole process of mechanical response of lining structures subjected to active fault dislocation is obtained. The performance of lining structures is also evaluated based on the scale and distribution of concrete damage conditions. The results indicate the reliability of flexible joints, which are suggested as an effective countermeasure for tunnel design when active faults are present. The proposed numerical approach is also verified efficient as an evaluation tool for the performance of lining structures in tunnel operation period.

1.
Introduction

Recently, a number of water diversion projects are scheduled or under construction in the western region of China, so as to effectively solve the problem of regional water shortage. The water conveyance tunnels are usually adopted because the western region of China is mountainous. The water conveyance tunnels always extend such a long distance that many complicated geological units are encountered along the route. The active faults is a typical geological structure and also a difficult ground for tunnel construction. The tunnel design codes both from China and other major countries all recommend avoiding active faults as the primary strategy but provide very little knowledge on how to cross active faults for engineering structures. The long-term safety of tunnels across active faults remains an alive issue because active faults is unavoidable for long distance route projects.

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