ABSTRACT
Watercare’s Central Interceptor Project is the largest wastewater project in New Zealand, a 16.2 km underground wastewater tunnel from Māngere Wastewater Treatment Plant to Point Erin in central Auckland. The 4.5m inner diameter main tunnel is being constructed using an Earth Pressure Balance (EPB) Tunnel Boring Machine, called Hiwa-i-te-Rangi, at depths between 15m and 110m below ground level, through a variety of Auckland’s geological and hydrogeological conditions. Tunnel excavation environment in geological formations with varying engineering properties pose a significant risk to EPB tunneling. The effect of EPB pressure and interdependencies between performance parameters in EPB tunneling is starting to gain attention of tunnel engineers for technical optimization. This paper provides a case study with insights on the effect of geotechnical properties on EPB performance – specifically for Auckland geology – thus providing technical context to tunneling feasibility in Auckland and potential to influence designing more efficient EPB-TBMs. The study summarizes the effect of EPB pressure and operational constraints on TBM performance i.e., on thrust force, torque, penetration, advance rate and settlement, using actual operational data from the mixed ground conditions on the Central Interceptor project in Auckland.
