ABSTRACT
Most of railway and motorway tunnels were built more than 50 years ago and consequently are approaching or have already reached their design working lifetime. The lining of these tunnels have been subjected to ageing and degradation with impact on their functionality and user’s safety. For these tunnels, it is necessary not only to provide the periodical inspection and ordinary maintenance of the tunnel lining, as local repair and rehabilitation, but also to carry out a complete check-up of the whole tunnel structure to evaluate how to extend the service state of tunnel structure. The experience pointed out the main faults for these tunnels stay in the concrete used for the definite lining, regarding both the quality and durability and the modes of put-on place. The main faults registered by in situ inspections (cores and GPR) are poor quality of the concrete with very low UCS, unbundling of ready mixed concrete, minor thickness in respect to the designed one and presence of voids behind the lining. The geological/geotechnical conditions of the surroundings soil/rock mass and the stress and strain conditions around the periphery and into the tunnel lining rarely play significant role. In order to achieve maintenance full revamping, it is essential to acquire all the information through direct inspection, geophysical investigation and in situ monitoring and to set up an evaluation method of tunnel health by back analyses of static condition, and, if relevant damages rise up, to identify the actual causes of the problem for defining the repair works. An integrated approach for the assessment of the tunnel structure conditions based on the RES (Rock Engineering Systems) interaction matrix is useful taking into consideration geological, hydrogeological and geotechnical conditions along the tunnel, structural performance, tunnel surveillance and inspection results, service condition and guideline for the maintenance, repair and rehabilitation works.
