By Meg Davis, Industry Marketing Director, Road and Bridge, Bentley Systems

Takitimu North Link Project uses a model‑based digital approach for design and construction to reduce carbon emissions and improve construction efficiency.

Takitimu North Link is a new road being constructed to connect the North Island communities of Tauranga and Ōmokoroa by providing a four-lane corridor between State Highway 29/Takitimu Drive Toll Road and State Highway 2/Ōmokoroa Road intersection. Tauranga is one of New Zealand’s fastest-growing cities – it has experienced an 18 per cent increase in population growth over the past few years, which has strained the road network. The existing route is a two-lane highway carrying 20,000 vehicles across the Wairoa River, and will not be able to accommodate the expected growth of over 30,000 vehicles in the area. 

The new expressway will significantly improve safety and ease congestion, as well as offer people more varied travel options, including a new shared active mode path for walking and cycling, and provision for managed lanes. The project, part of the government’s New Zealand Upgrade Programme, is also important, as it will support economic development and population growth in the Western Bay of Plenty.

The Takitimu North Link project is being constructed in two stages by Waka Kotahi NZ Transport Agency. Stage one is a design and construction project for a 6.8-kilometre expressway, including 10 bridges and a separated shared path. It is being built by a Fulton Hogan and HEB joint venture (FH/HEB JV) in a challenging natural environment constrained by existing infrastructure and developments. The area is largely volcanic in origin, but the subsurface materials vary considerably and range from fill, alluvial clays, silts and sands, to weathered volcanic ashes. In addition, the groundwater levels are shallow in low-lying flood plains and deep in areas of higher elevation.

The project team needed to find solutions to rapidly create a road design in these challenging conditions, meet the needs of Waka Kotahi and the community, and communicate and collaborate with the construction partners while also minimising risk. With Beca as the lead design consultant, the team wanted an integrated, model-based digital delivery approach to address the site complexities and coordinate the large, multidisciplinary project team.

The team used the Bentley iTwin platform for their model-based approach on the project. An iTwin is a 3D visualisation tool that designers, constructors, Waka Kotahi, and their stakeholders can use to understand and influence the solution. It means that all the different disciplines involved in building a road – such as designers, and geotechnical, structural and environmental engineers – can share their designs and information in one place.

The enhanced integration with other disciplines using 3D modelling software created project improvements for design and construction delivery. 

‘Waka Kotahi had a requirement for step change, and one of the initiatives proposed by the FH/HEB JV was to implement digital modelling on this project. We were fortunate because many members of the team were already using Bentley’s 3D design tools for road, bridge and subsurface design,’ says Ross Brown, Beca’s Technical Director. 

Beca created 3D models of the ground conditions to inform road and drainage design, earthworks, and structural design, as well as to optimise and model volumes for the mass haul of fill to meet the needs of the design.

Option selection during the tender phase required quick, realistic visualisations so that the design team, constructors, and the client could understand the evolving plan. Additionally, if required, it would help them make adjustments in real time. The design team leveraged OpenRoads ConceptStation to explore these options. 

Every five weeks during the tender phase, interactive meetings were held with the tender evaluation team from Waka Kotahi. The team created a visualisation model using LumenRT, giving them a visual representation of the immersive corridor modelling capabilities and multidisciplinary coordination. It also created 3D line styles in OpenRoads Designer to speed up the export process.

With the roads team already using OpenRoads, the geotechnical team began modelling the subsurface strata in Leapfrog. Leapfrog data was then imported by the road designers and used in their design profiles. With poor ground conditions recognised as a delivery risk, a 3D geological model was developed in Leapfrog using the geotechnical investigation data. The team then used this model within OpenRoads Designer to maintain cuts within the usable volcanic ash layer wherever possible, as this was the stronger soil material and can be cut to a steeper slope. The model was then used to inform geotechnical design and earthworks modelling for the assessment of volumes of the various materials for the project mass haul diagram.

By using an OpenBridge Modeler design that was linked to the road alignment model during the project design phase, the bridge modelling team could easily cope with alignment changes without adversely affecting their bridge design work. As the project progressed, the team frequently included additional data, requiring changes to the model. The use of the Bentley solutions allowed designers to adapt to these changes easily.

To deliver this project on time during the COVID-19 pandemic, with lockdowns happening during the tender and detailed design delivery phase, it was essential to have a connected data environment. ProjectWise was the tool of choice, as it allowed seamless collaboration across the disciplines to accelerate modelling time, and ensure accurate and real-time data sharing when most of the designers on the project were working from home.

A focal point in designing and delivering the Takitimu North Link was including sustainability as part of the New Zealand Upgrade Programme. In addition to improved environmental outcomes, the digital twin enabled a host of benefits throughout the design stage, which will continue through the construction phase. Using the iTwin Platform helped reduce carbon emissions for the project’s construction by at least 10 per cent. The platform helped optimise the design to enable earth cuts to be used as fill or deposited on site. The project did not require any imported fill, and no material has to be carted off site due to the optimisation process with the constructors. The local road network has been freed of a potential 22,000 truck movements, and 900,000 kilometres of journeys, which is estimated to be around a 560-tonne reduction in carbon emissions.

Leveraging Bentley’s open modelling applications, the design and construct team established a connected data environment and digital twin that will simplify construction in the constrained location. Through collaborative digital modeling and 3D visualisation, they reduced modelling time by an estimated 15 per cent and improved design efficiencies by 20 per cent, while achieving higher-quality deliverables compared to previous design methods. The digital twin enables data integration for construction activities and for possible future management and maintenance of roadway operations, which is under development by the project team.

To find out more about the project, visit www.nzta.govt.nz/takitimunorth.