Ara Tuhono - Puhoi to Wellsford - GHD

Ara Tūhono - Pūhoi to Wellsford - Road of National Significance

Project Summary

The purpose of this project is to improve State Highway 1 between Pūhoi and Wellsford in the northern Auckland region.

Route Selection to Scheme Assessment for the ~40km extension of the Auckland Motorway network, from the north of the Johnston Hill Tunnels at Pūhoi, to Wellsford.
The study area covered over 550km² of rugged hill forest and farm land, with over 1,000km of route design produced and documented using 12d Model software. The ‘Preferred Route’ for the section from Pūhoi to Warkworth was later announced following public consultation.

The Challenge

GIS was required to identify potential routes, based on weighted constraints e.g. Social, Economic, Environmental, and topography.
Some 30+ long listed routes were to have alignments created and earthworks produced for comparative and multi-criteria analysis to be carried out.
Within the study area, 14 geological terrain systems were identified, with highly varied characteristics and irregular boundaries. The design of any earthworks in 12d Model needed to take into account the high variability of the geology along the route, as well as with depth of cut/fill.
The process needed to be robust, flexible and consistent across all routes identified, and fast, given the length of each route and quantity to be assessed over a short project time frame.

The Solution

Decisional Templates were the obvious/traditional tool to use to cater for the varied batter profiles given the depth of the alignment from the existing ground.
These were then taken one step further and given a form of spatial awareness so batter profiles could be suited to the varied geological terrain systems encountered along the alignment, taking away the need for designer intervention at terrain system boundaries.
This drastically sped up the initial creation of alignments, and resultant fine tuning to meet desired cut/fill ratios.
The process of adding spatial awareness to the decisional template was largely straightforward, albeit slightly abstract; the various terrain systems were assigned elevations and triangulated to create a tin with various plateaus. This was the basis of the spatial decision making, with all batter scenarios contained within the one template and covering the entire route (excluding overrides for structures where required).
The completed routes (including e.g. interchanges, tunnels, viaducts and MSE embankments) were documented straight out of 12d Model to DWG format for compliance with company QA, and to PDF for detailed engineering assessment where required. Volumes were sent to Excel and into GIS using shape files for back analysis of social/ environmental effects and potential land requirement.

The Result

Benefits of the project include reducing congestion during peak periods, as well as improving economic development and tourism opportunities in Northland.