Auckland City Rail Link – Cavidrain Invert

The Auckland City Rail Link (CRL) is New Zealand’s largest ever transport infrastructure project. The $5.5 billion development features a 3.45 km underground twin-tunnel network, designed to double the the city’s rail capacity and significantly reduce commute times. The CRL project significantly improves network connectivity and reliability to help meet Auckland’s growing public transport demand.

CHALLENGE

Tunnel waterproofing and drainage systems play a critical function in preventing corrosive damage to reinforced concrete floors and to stop uplift pressures damaging the structure. Traditionally, a thick crushed rock drainage blanket with perforated pipes is installed. However, this method is prone to localised calcareous blockages, involves additional excavation and requires the delivery and placement of expensive granular drainage stone along the length of the tunnel.

SOLUTION

An advanced, cost-effective geocomposite drainage alternative was specified to achieve a much faster installation across large, flat areas of the tunnel slab and efficiently transport groundwater away. ABG Cavidrain 40 and Cavidrain 60 drainage products were installed to provide high drainage capacity and long-term performance, used as both an invert drainage solution beneath the base slab and for the tunnel walls between the primary structural tunnel lining and the secondary internal concrete finish.

For the tunnel floor construction, the ABG Cavidrain Invert HDPE drainage layer was installed over the prepared formation before the concrete slab was cast directly into it. This provides a continuous drainage void below the slab, ensuring any infiltration water moves freely without ponding or exerting uplift pressure. The Cavidrain Invert maintains high in-plane flow capacity and provides resistance to mineral calcification.

Cavidrain was particularly useful on the CRL underground project in central Auckland in situation where the tunnels and station boxes are beneath the groundwater table.

The Link Alliance integrated consortium was the design and build partnership for the Auckland City Rail Link (CRL) tunnels and stations and consisted of the following companies: VINCI Construction Grands Projets (lead contractor), Downer NZ, Soletanche Bachy International NZ, WSP New Zealand, AECOM New Zealand, Tonkin + Taylor, City Rail Link Ltd (CRL Ltd – client)