Waterview Connection Project Cross Passage Tunnels: Safety in Design and Construction

This article was first presented at the World Tunnel Conference (WTC) 2018 in Dubai, United Arab Emirates.

The Waterview Connection is the final 5km link to complete the NZ Transport Agency’s Western Ring Route motorway around Auckland. The Waterview Connection is the largest and most complex road infrastructure project ever undertaken in New Zealand. A 14.4m outside diameter Earth Pressure Balanced (EPB) Tunnel Boring Machine (TBM) was used to complete the twin 2.4km long tunnels, located at the heart of the scheme. 

The Well-Connected Alliance delivering the project recognized the importance of identifying and mitigating hazards throughout all phases of the project. As a result, a rigorous safety-in-design procedure was mandated for all design packages so that safety risks were designed out wherever possible. The risk mitigation measures were implemented in construction works, with multiple verification mechanisms in place.

This paper describes key design and construction safety-in-design features that were developed for the 16 cross passages linking the two mainline tunnels. Such measures included a clear and robust safe man entry procedure for working under green shotcrete; excavation and lining geometry optimized for risk mitigation; extensive shotcrete trials designed for requisite early strength gain and all anticipated conditions; canopy tube ground support; and targeted grouting in high permeability zones. Safe benched excavation sequencing was adopted to address the confined nature of the relatively small, short cross passage tunnels. Critical construction activities were monitored with instrumentation to ensure safety of personnel at all times. This case study provides learnings from the project’s safety-in-design and construction initiatives, which set a benchmark for the industry practice. The Waterview Connection cross passage tunnels were all successfully completed on time without any accidents or lost time injury.