The Permit to Tunnel process adopted on Australian infrastructure projects.

This paper discusses the Permit to Tunnel (PTT) process adopted on recent major Australian infrastructure projects such as Cross River Rail (Brisbane), Westconnex (Sydney), Melbourne Metro and Sydney Metro. Following two incidents on tunnelling projects in Sydney, the PTT was introduced in 2009 for the construction of Brisbane's Airport Link. The PTT is the most significant process implemented by the tunnelling industry to improve ground-related construction safety and quality. The PTT process was developed to review and document encountered ground conditions, available monitoring data and observed ground behaviour and, as a result, to assign ground support over a defined period and extent. It assists the tunnelling contractor and the client in verifying that construction is being undertaken in accordance with the certified design. This includes determining whether the encountered ground conditions fall within the applicable limits of the designed ground support selection criteria, and checking that excavation-induced ground movements and other key performance indicators are within allowable bounds. This paper describes the intent of the PTT, its inputs and outputs, roles and responsibilities, benefits and potential opportunities for improvement from a contractor's and designer's point of view. Recommendations for the effective setup of a PTT process, along with examples from recent Australian projects are provided. In addition, the paper deals with the associated Monitoring Action Team (MAT) and design change processes. [ABSTRACT FROM AUTHOR]