Customer: Fletcher Acciona Joint Venture Contract: Construct only Location: Warkworth, Auckland

McConnell Dowell (MCD) was awarded the construction of the E530 Culvert as part of the Ara Tūhono – Pūhoi to Warkworth project in May 2021.

The E530 Culvert is being constructed as part of the widening of State Highway 1 (SH1) between Hudson Road and Pukerito (Northern Connection). This is a new 2.4m diameter reinforced concrete pipeline to replace an existing, smaller culvert. The new culvert will divert and connect two existing watercourses, approximately 110m apart, via an inlet and outlet structure with low flow channels.

The scope of works includes the construction and installation of:

• 4m dia. IWJ / RCRRJ pipe approximately 40m by pipe jacking and 70m by open cut methods
• A temporary launch shaft for the pipe jack
• A temporary receiving pit for the pipe jack
• Permanent headwall and wingwall structures with associated aprons at the inlet and outlet
• Backfill over the installed pipeline and around inlet/outlet structures
• A continuous handrail safety barrier to headwall and wingwall structures
• Fish passage baffles in the completed culvert

The challenge

The culvert crosses underneath SH1, parallel to the proposed intersection of Matakana Link Road which is now under construction. The area has significant construction activity due to the current roading projects and has extremely high traffic volumes.

The solution

Instead of digging up the road in two halves, building the culvert and then burying it again, it is being hydraulically pushed under SH1 using advanced Pipe Jacking technology.

Excavation will be carried out primarily using a hydraulic backhoe mounted inside the first pipe, with spoil removed by portable conveyors at the face and rail-mounted muck skips to manually haul the spoil out of the tunnel and be lifted out by crane. The precast jacking pipes will be installed on a cradle at the bottom of the jacking pit at the end of each advance. The entire pipeline and shield are pushed into the ground by means of a jacking frame fixed onto the back wall of the shaft. Tunnel services including lighting, power, communications, compressed air and ventilation are extended as required as the excavation progresses.

Pipe Jacking is a Tunnelling Operation in accordance with the Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations 2016. The legislation and rules are the same as for any other major underground infrastructure project.

Key to success

The culvert is installed by means of a semi-mechanised open-face form of tunnelling using a shield, mechanical and hand excavation to deal with a wide variety of ground conditions and obstacles which may be encountered.

Because this is classed as a mining operation, the tunnelling industry carries a long-standing tradition of placing a small statue/shrine to Saint Barbara at the tunnel portal to provide protection to all those who work on the project.

Construction started in November 2021 and works were completed in March 2022.