Wairarapa Tunnels Renewals (WMUP3)

Supporting one of KiwiRail and Greater Wellington Regional Council’s critical and high risk renewal projects in delivery and design.

Vitruvius supported KiwiRail’s Wellington Metro Upgrade Programme (WMUP) management team by delivering a range of critical roles across the WMUP III Wairarapa Tunnels Renewals Project. What commenced as drainage design, delivery support and MSQA services, led by Matt Stuart, evolved as the project progressed to include Engineer’s Representative services for the drainage contract, Project Director leadership provided by Neil Mason, and additional project engineering and project management support to enable successful delivery of the works within a complex operational environment.

The Remutaka Tunnel (renamed from Rimutaka in 2017), is an 8.8km single bore Railway tunnel constructed from 1951 to 1954 and opened in November 1955, replacing the Rimutaka Incline railway that had made its way over the Remutaka Hills since 1878 (now known as the Rail Trail to local hikers and bikers). The tunnel runs through New Zealand’s Remutaka Range and is the second longest railway tunnel in the country. The location of this tunnel and the regular use for freight and passenger services makes maintenance periods difficult to come by.

The majority of the components within this tunnel have not been replaced since the track was first constructed in the 1950s and the windows for renewals are particularly short given the amount of drainage and track that is to be renewed throughout, requiring an innovative and collaborative approach to construction. The hard deadlines for construction require designers, contractors, project managers, programmers, construction managers and commercial teams to work closely together to provide a proactive and safe plan of attack. The success of this project will come down to each stakeholder feeling a part of the team and buying into the project goals.

Drainage Design and Delivery

Designing a drainage system in a tunnel environment that is able to be safely removed, recycled at the next renewal and takes into account productivity/available track time is no easy feat. Vitruvius led the drainage design for both tunnels, responding to a number of complex principal requirements. A key consideration was designing a system capable of withstanding loads from track panel lifters used during track relay works through the tunnels. The solution also had to convey an unknown flow rate through the short circa 650m Maoribank and the significantly longer circa 8.8km Remutaka tunnel. Following initial site investigations, remote flow rate monitoring was installed to aid in the design of the drainage system and water samples were collected to test for the presence of contaminants and iron.

An initial concept design was produced for the internal tunnel drainage only with a number of recommendations to the client to ensure a whole system approach to upgrading the drainage had been considered. In order to progress to detailed design, Vitruvius requested further surveys be undertaken of the external tunnel drainage to identify the asset condition, location and outfalls. This meant a full system design could be provided to prevent downstream defects causing an overflow of the tunnel drainage.

The detailed design offered two solutions for differing scenarios within the tunnel, the more complex of the two for higher flow rates comprised of a Megaflo system throughout the tunnel with a layer of drainage metal, a filter layer of sand and geofabric working in unison to increase the design life of the solution and a walkway that provided adequate underfoot conditions for maintenance. For increased efficiency within the tunnel a second option for lower flow rates was also proposed that allowed for the removal of the Megaflo and sand from areas of the tunnel where the flow rate was considered lower than 0.2l per s.

The design underwent review, during which the construction team requested amendments to enable faster installation within the available work windows. Rapid turnaround of design reviews and approvals allowed these changes to be incorporated efficiently, resulting in a solution that was well‑suited to the tunnel environment and could be installed by the contractor within the permitted timeframes. The value of having a strong design manager and early contractor involvement, working collaboratively with the client, was clearly demonstrated in the lead‑up to site commencement.

Civil and Laydowns

On short notice, Vitruvius was engaged to act as Principal’s Project Manager and Engineer’s Representative for the newly awarded NZS 3915 contract to construct three laydown areas as part of the enabling works. With commencement deadlines looming and several critical risks unresolved, a proactive and collaborative approach was required to mitigate potential impacts to programme.

Through coordinated stakeholder engagement, legal and planning reviews, and the development of strong working relationships across multiple risk areas, these risks were effectively managed. This enabled the critical laydown works to commence and be completed without disruption to the project’s critical path drainage works. Vitruvius is proud to have supported the project team in navigating these challenges and delivering outcomes aligned to a shared project goal.

Project Director

Neil Mason, who was Managing Director of Vitruvius at the time, stepped in as Project Director for the Wairarapa Tunnels 1 and 2 delivery to support best practice long tunnel project delivery. Having worked on all of Aotearoa New Zealand’s long rail tunnels in some capacity, Neil brought a wealth of experience in the safe and practical delivery of complex tunnel projects. This depth of experience supported the WMUP team in delivering the programme of works within a highly complex safety and stakeholder environment – the kind of complexity Vitruvius thrives in.

Vitruvius initially began on the project in February 2023 with support and advisory requirements increasing over time. We were grateful to have joined our valued client on this project delivery journey and bring not just our rail knowledge, but our project delivery expertise as well in support of their project goals to safely deliver these critical works to programme. So far so good!

Vitruvius would like to acknowledge all of the fantastic people that are involved in delivering this project and their companies – Our Client and Partner KiwiRail, consultants Tonkin & Taylor, WSP and Aurecon, Track and Drainage construction – Titan Contracting Group, Civil and Laydowns – Mills Albert, Tunnel Ventilation – BEST Engineering, and the vast network of sub-contractors and suppliers that make a project of this scale a success.