ABSTRACT

The stability of a tunnel must be achieved and firmly maintained during each stage of excavation for worker safety, to prevent any partial or large scale collapse, and to allow for the installation of any required final lining. Tunnel stability assessments should be performed at each stage of tunnel design and regularly updated as new information becomes available particularly after the completion of a site investigation and for any changes to tunnel geometry. Tunnel stability assessments are required for a thorough understanding of the behaviour of the rock conditions during excavation and for the design of safe and practical rock support and linings. The main challenge for these assessments is the evaluation and selection of representative rock parameters required for input into these software programs. Representative geotechnical parameters for stability analyses should be selected based on a thorough review and evaluation of the characterization information as well as from consideration of information from similar projects located in similar geological conditions.