ABSTRACT
Precast segments used in tunnels excavated by Tunnel Boring Machines, are often manufactured offsite in suitable facilities and subject to logistics and handling until they are finally assembled in the tunnel. Throughout this process of production, construction and during the service life of the tunnel, segments can have defects, or they can be damaged, and their assessment and repairs will be in many cases required. This paper presents a holistic approach to the needs for repairs. Before any repair, an agreement for traceability, survey and monitoring the lining’s damages are required and this is also explained. An appropriate repair strategy approach, which sometimes have a relevant impact in time and cost in the projects, is presented in the paper together with the classification of the different defect types, all based on the reliability of the structure. The paper highlights the causes of damages, common occurrences, and trends across different types of precast facilities and tunnels.
Damages need to be assessed to ensure that the structural reliability is restored to the original design intent performance. The factors of safety assumed in the design shall be maintained and the durability of the structure for the whole service life needs to be achieved following any repair activity. This paper discusses how the structural reliability can be ensured in line with the principles set out in BS EN 1990. Additionally, it is explained how products and systems for repair and their testing, as defined in BS EN 1504 or ACI 562, can be adopted to help to define a tunnel lining repair procedure, but in some cases, is required to go beyond the current repair standards because they are not enough to ensure the reliability for the manufacturing requirements, materials properties, high performance and design life, for which the concrete tunnel segments are designed.
