Herrenknecht TBM Breaks Through in New Zealand
The Waterview Connection in Auckland, New Zealand, is being constructed by the Well Connected Alliance (NZ Transport Agency, Fletcher Construction, McConnell Dowell Constructors, Parsons Brinkerhoff, Beca Infrastructure, Tonkin &Taylor and Obayashi Corp.), on behalf of the New Zealand Government to deliver a direct motorway link between the Central Business District and the International Airport. The completed project will allow more reliable and reduced traveling times, improve regional transport links, and ease congestion on the main motorway route through central Auckland.
The project comprises two bored tunnels with an approximate length of 2.4 km (1.5 miles) and an inner diameter of 13.1 m (43 ft) accommodating three lanes of traffic each. New Zealand’s then Transport Minister Gerry Brownlee said during the celebration of the start of tunneling on Oct, 31, 2013: “This section of new motorway will link the southwestern and northwestern motorways, completing the long awaited Western Ring Route. It represents a significant investment by the Government in providing the strategic motorway system Auckland needs to support its population and economic growth.”
The Well Connected Alliance (WCA) opted for an earth pressure balance (EPB) shield with a shield diameter of 14.41 m (47.25 ft) to drive the two tunnels. Herrenknecht designed and delivered an EPB shield customized with respect to the project’s geological and logistic demands, including a customized back-up system for the installation of service culverts and associated backfill independent from the excavation process. The TBM was designed by Herrenknecht in Germany and built at the company’s factory in Guangzhou, China. The key components such as main drive, erector and hydraulic station were supplied from Germany. It was delivered to the jobsite on time after a design and manufacturing process of 14 months.
A school pupil from South Auckland gave the Herrenknecht EPB shield its name: Alice. The inspiration was the main character from the children’s book “Alice in Wonderland.”
Apart from the large-diameter profile, the excavation process had to deal with cover above the tunnel crown of a minimum of 10 m (33 ft) at the portals and a maximum cover of up to 40 m (131 ft). Additionaly, tunneling under Auckland’s suburbs included the demand of controlling settlement with maximum water pressures at the tunnel invert of approximately 6 bar. The tunnels’ geology was characterized as varying between extremely weak locked sands, siltstone, alternating siltstone and sandstone, very weak to moderately and well-cemented sandstone as well as volcanoclastic grit/sandstone. The typical material strengths were estimated to be below 5 MPa (725 psi) with a defined but small risk that the tunnels might intersect layers of cemented sandstone with unconfined compressive strengths of up to 120 MPa (17,500 psi). The machine was designed according to the predicted geology, specifically the cutting wheel.
Cutting Wheel Design
The EPB shield has an overall length of 87 m (285 ft) including backup gantries. The cutting wheel with a 14.46 m (47.5 ft) diameter is of star type design with eight main plus eight auxiliary spokes and with an arrangement of disc cutters, scrapers and buckets for bi-directional use. The cutting tools can be changed from the rear area. About half of the disc cutters were replaced by rippers during the first drive in response to the encountered geological conditions, with the option to easily change back to disc cutters if needed.
The opening ratio of 45% had to be a compromise between the need for sufficient opening size – to permit an unrestricted flow of excavated muck in order to prevent clogging – and the need to secure the excavation in case of facing layers with strengths of up to 120 MPa. In consideration of the expected abrasive nature of the prevailing ground conditions, the cutting wheel was designed with wear protection in the face and gauge area and on the back of the cutting wheel, as well as with a hydraulic wear detection system on the cutting wheel comprising two pins in the gauge area, five pins in the face area and one strip steel structure.
The first TBM drive toward the North portal showed that the expected clogging issue was not encountered. This was due to an appropriate cutting wheel design in combination with efficient conditioning management, e.g. the adding of water in quantities of up to 200 m3/h (880 gpm) into the working chamber. The optimized management of conditioning and the well adapted tool management led to the fact that the wear of the cutting tools was significantly reduced during both drives.
The machine was designed with a nominal thrust force of 199,504 kN (22,500 tons) and a maximum torque of 82,546 kNm (60,882,805 ft-lbs). The machine was powered by 24 electric motors of each 350 kW generating a total power of 8,400 kW. The machine was designed for an operating pressure of 6 bar with maximum expected face pressures of 5.3 bar. All seals, such as main drive and tailskin seals, were designed to cope with maximum pressures of 6 bar.
Secondary Tunnel Installation System
A main feature of the project and a mayor contributor to its success was the secondary tunnel installation system, designed and built by Herrenknecht specifically for the Waterview Connection project. Its task was the installation of the precast invert concrete segments (culverts) that make up the service tunnel within the tunnel profile containing all electrical power and communication cables. It has a total length of 96 m (315 ft), is 12 m in height (39 ft) and has a weight of 400 t (440 US tons). This system consists of four components and is designed with a sliding platform, a steel ramp section, a culvert placing gantry with a culvert handling crane and an auxiliary culvert protection. The system runs on bogies behind the TBM.
The so-called culvert gantry followed the TBM and worked independently from the excavation process. The independence pushed the efficiency of both, the tunnelling as well as the installation of the invert segments. Also, the design of the secondary tunnel installation system allowed for a shorter TBM which was an important benefit when turning the machine around after the first tunnel (see below).
Tunneling Excavation of the first, the northbound tunnel, started following the launch ceremony on Oct. 31, 2013. Only 11 months later the successfull breakthrough was achieved on Sept. 29, 2014. As early as Dec. 15, 2014 the EPB Shield started excavating the second tunnel after the challenging turnaround procedure had been completed. Final breakthrough was celebrated on Oct. 19, 2015. Tunneling rates of up to 127 m (416 ft) per week had been achieved. New Zealand’s Transport Minister Simon Bridges commented on the occasion of the breakthrough: “The government couldn’t have asked for more from the $1.4 billion project which has so far come in on time and on budget.”
Turnaround of the TBM in the Northern Portal Trench
A TBM design aspect was focused on the completion of the first tunnel section. After the breakthrough on Sept. 29, 2014, the machine had to be turned around and pushed sidewise to excavate in the opposite direction toward the south portal. Due to limited space available in the northern portal trench with dimensions of 40 x 40 m (130 x 130 ft), the TBM design was adapted to ease the turnaround of the shield and tunneling system. The shield and the backup gantries were designed as short as possible. The shield has a length of 12.4 m (40 ft) with a short trailer of three gantries, with an overall length of 87 m (285 ft). The first backup gantry directly behind the TBM carries most of the relevant TBM installations.
After breakthrough of the TBM the shield was moved on the TBM cradle. Then both, the shield and the cradle were moved on steel plates that were placed on the trench floor and greased to facilitate the cradle movement. The shield, including the cradle, was then turned by 180 degrees. For the turnaround of the backup, a similar process was implemented. On Dec. 15, 2014, the TBM started excavating the second parallel tunnel toward the south with backup gantry 1 and gantry 2.1 (temporary gantry).
All tunneling-related processes were monitored with a system comprising two major components of the IRIS program family, IRIS.tunnel and IRIS.geomonitoring, by VMT GmbH, a Herrenknecht Group company. IRIS.tunnel provides comprehensive monitoring of machine and navigation data to the tunnel team and other project partners.
In combination with the geomonitoring component, this monitoring solution became much more powerful. It allowed for correlation of TBM data with results of continuous surface monitoring conducted along the tunnel alignment. Another extension of functionality has been provided to WCA by integrating data from VMT’s Segment Documentation System (SDS) directly and automatically into IRIS. For the machine’s navigation Auckland’s tunnelers relied on VMT’s TUnIS, a laser-based high-precision navigation system.
The Waterview Connection is New Zealand’s largest and most ambitious road infrastructure project. Its key element, two 2.4km-long dual-lane road tunnels were excavated and lined by a Herrenknecht EPB Shield. The tunnelling success was based on one hand on the project specific machine design. This included a newly developed secondary tunnel installation system. On the other hand, the machine crossed the finish line on time and on budget because of a constructive and fair partnership between the competent client’s jobsite team and the machine supplier.
Physical works on the Waterview Connection project are due to be completed this December and the New Zealand Transport Agency plans to open the project – the twin tunnels and the adjoining interchange linking Auckland’s Northwestern and Southwestern motorways – in early 2017.
Dr. Karin Bäppler is Head of Geotechnics & Consulting for Traffic Tunneling at Herrenknecht.