Project: Alice - New Zealand's Tunnel Boring Machine

By: Jenny Pretorius and Well-Connected Alliance, Photography by: courtesy of NZ Transport Agency

Date: 10.12.2013

At 87m long, Alice is the largest machine of her kind ever used in Australasia and the tenth largest of her kind in the world. The largest machine (currently at work in Seattle) has a diameter of 17.5m. Alice

Alice will drill two holes, each big enough for a three-lane motorway, over a period of two years. The art work Te Haerenga Hou, meaning New Journey, was designed especially for the project by artist Graham Tipene. Alice

Alice being built. The structure is made from special steel to handle extreme pressure. The wiring and motor cables are all made of copper and weigh 10 tonnes. There’s gold wiring on the computer systems and programmable controllers. Alice

Beautiful Alice, New Zealand’s tunnel boring machine (TBM), is just about assembled and expected to start slicing up the concrete slab covering the entrance to her 2.4km northbound journey to Waterview in early November.

Project: Alice - New Zealand's Tunnel Boring Machine

Inch by inch into our heart and soil

More than 20,000 admirers wished Alice the TBM an enthusiastic bon voyage at the 13 October open day hosted by Well-Connected Alliance, the tunnel's builders, at the southern entrance to the Waterview tunnel.

Spokesperson for the alliance, Gez Johns, says the day was a resounding success. "The meeting between Alice and her public went well. The project is not simply about roads, but about connections, connecting people. It is not just a tunnel, but a complete urban development project focused on improving outcomes for all, for the communities involved as well as for the whole of New Zealand."

Although all eyes are on the sleek and elegant 3600t TBM, Johns says the work on both sides of the tunnels-in-waiting that back up her megastar performance is just as inspiring in scope. He updated DOW with information about the project's progress at the southern tunnel entrance so far.

Alice is fully built, but like the rest of us, her 16-strong team plus pilot need a WOF before she can hit the road. Her electronic systems are being tested in preparation for the anticipated first cut into the Allan Wood Reserve face in early November.

As Alice tunnels underground, spoil will be offloaded onto a conveyor system built progressively in her wake. The conveyor system will exit through the entrance of the tunnel and continue 750 metres through the site to the spoil-handling building. Both the site conveyor system and spoil-handling building are now ready for work.

When working at its maximum capacity, the 1.2m-wide strengthened rubber conveyor belt can ship 3500 tonnes of spoil per hour and runs at 3.6 metres per second. The conveyor structure will elevate from about 4.8 metres in the tunnel portal to 14 metres high at the spoil-handling building entrance over a distance of 700m. Eventually, the conveyor system will be 5km long.

For every two metres that Alice progresses, or the width of one tunnel ring, 330 cubic metres of spoil is produced. Approximately 2.5 million tonnes of spoil — 800,000 cubic metres of ground, enough to fill 320 Olympic-size pools — will be removed from the tunnels by the project's end.

Comments Johns: "It is a huge structure, but it reduces the impact on our neighbours significantly. The belt runs in a soundproof casing that contains all noise and allows round-the-clock operation. The conveyor system and the location of our spoil-handling facility, adjacent to where SH20 currently ends, allow us to remove 50,000 truck movements from the local road network."

The 170m-long spoil-handing building contains eight individual bins with a total capacity of 9000 cubic metres. The building is acoustically lined to allow round-the-clock loading out. The spoil will remain there for 24 hours to dewater and will then be trucked to a quarry in Wiri, South Auckland.

A purpose-built facility in East Tamaki makes the 2m-wide, 450mm-thick segments by casting concrete in a reusable mould. The concrete is then cured in the best conditions, so it achieves the required strength and hardness. The yard, where the concrete tunnel segments will be held ready for Alice's work, is complete and ready to go. It holds 320 segments, or 32 complete rings, at any time. This equates to about two and a half days of TBM production. Segments arrive from East Tamaki in threes via truck and trailer and are then moved to the TBM one at a time by custom-built transporters.

Areas of Oakley Creek, also called Te Auanga, have now been designed to replicate the flow of a more naturalised stream than the excavated drainage channel it has been for a long time. The new stream will better accommodate flood flows. The design of the creek includes gentle battered slopes leading down to the stream, providing access to bird, fish and insect life in their new environment.

The green areas next to the creek have been planted exclusively with native plants suited to the environment. The area will be open to the public as a new reserve when the Waterview Connection is completed in early 2017, and will include footpaths, shared-use cycleways and footbridges crossing the creek and the motorway.

Why does New Zealand's TBM have a female name? This is a tradition with a long history. It arose from people who believed a religious figure, Santa Barbara, is the patron saint for artillerymen, armourers, military engineers, gunsmiths, miners, and anyone else who works with cannons and explosives. Tunnellers, being underground workers, consequently look to Saint Barbara for protection. As a result, machines that work underground are always given female names.

Who the heck is Alice?

Fifty-five-million dollar Alice is an earth pressure balance machine (EPBM). The primary purpose of an EPBM is to maintain the pressure in the shield's cutting head to that of the surrounding area. As material is being removed at the tunnel face, Alice maintains the same pressure as the ground around her in her shield. This stops the ground from caving in as the same pressure is being maintained as the earth around it.

Herrenknecht, a leading manufacturer of this type of machine, built her in its plant in Guangzhou, China. She was transported in pieces and arrived home in July. It took three months to put her together again. A 600-tonne crane, Terex-Demag CC2800-1, was brought to site to lift the TBM components into the trench. Despite being only a temporary structure, the platform required deeper and longer piles than any of the permanent structures on the entire project.

Alice is made up of a shield and three cars, or gantries, that sit behind the shield. The cutting head at the front of the shield is made of thick steel and can be likened to a giant round grater that will grate away the earth.

There are two main parts to the shield: the tunnelling phase and the ring-building phase — the latter during which prefabricated concrete panels will be put in place to form the walls of the tunnel.

In the tunnelling phase, hydraulic thrust cylinders apply pressure of up to 22,800 tonnes to push the cutting wheel against the tunnel face. The cutting wheel rotates at speeds of up to 1.9 revolutions a minute. Twenty-four electric motors, with 8400kW of usable power generating 82,546kNm of torque, power the cutting wheel via the main drive.

The high pressure and torque enable the high-strength cutter to remove the soil at the tunnel face.

During the cutting process, soil is conditioned using a polymer injected along with water and compressed air into the cutting area through pipes in the rotary cutting head. These pipes are connected to injection nozzles at the front of the head, which spray the conditioning mixture on to the cutting face. Soil is conditioned so it does not clump and stick to the steel on the inside of the cutting head. It then takes on a toothpaste-like consistency and is easily removed from the cutting chamber.

With its rotating cutting wheel or shield at the cutting face, spoil — soil that has been injected with conditioners to make it more pliable — is removed at the tunnel face (1). The spoil enters the excavation chamber (3) through openings in the cutting wheel (2). It then mixes with soil mush that has already been removed. The thrust cylinder force is transferred to the soil mush via the pressure bulkhead (4), balancing the earth pressure. Excavated spoil is removed for disposal via a screw conveyor (6). As the screw conveyor removes the spoil from behind the shield, hydraulic cylinders continually drive the cutting head forward.

Ten concrete lining segments make up a tunnel ring in the tunnel-building phase of the shield. Each segment is two metres long and is installed by an erector. The erector picks up the segments that enter the TBM by way of a gantry and installs them one at a time.

Eventually 24,040 of these prefabricated tunnel-lining concrete segments will completely line the Waterview tunnels.

As Alice moves forward, she leaves a lined tunnel in her wake. Her propulsion system (5), which consists of cylinders around the circumference in the shield, pushes against this concrete lining to project the machine forward.

The tunnel-lining rings are positioned under atmospheric pressure by the erector in the shield behind the pressure bulkhead and then bolted in place. Grouting is continuously forced into the remaining gap between the segments' outer side and the soil through injection openings in the tailskin. The injection of the grout ensures there are no gaps between the excavated earth and the tunnel-lining rings installed, ensuring stability.

Behind the shield sits the back-up cars or gantries that house all the equipment needed to run Alice.

Interesting statistics

Depths Alice will work at: 15 to 45m below ground
Weight of Alice: 3600t, or about the same weight as 750 elephants
Cut diameter: 14.46m
Shield diameter: 14.41m
Cutting head: 19.2hp
Number of electric motors installed: 24 pieces
Motor power: 350kW
Total installed power: 8400kW
Maximum torque: 82,546kNm
Maximum rotation speed: 1.9rpm
Cooling system: 2600L/min 25˚C
Propulsion: 9.5rpm
No of cylinders: 56
Propulsion stroke: 3000mm
Max rate of cylinder extension: 80mm/min
Total thrust force: 228,000kN
Length of tunnelling machine: 12m
Maximum length of back-up car or gantry: 28m
Top speed: 8cm/min
How long Alice would take to drill to the centre of the earth: 2655 years