Projects

Harker has been working to complete Timaru District Council's MTSR Stage III sewer main renewal between Washdyke Lagoon and Smithfield. The break-through from each end of the first of three 400LM long tunnels occurred on Friday 14th November 2008 at 5am.

One crew was digging from the southern end with a tunnel boring machine, while the second crew was using traditional manual labour with explosives to break down the rock face from the northern end. The two tunnel halves were well-aligned when they met, enabling the tunnel boring machine to be removed from the northern shaft, dismantled and removed.

As part of the preparations for this contract, our EX50 backhoe TBM was heavily upgraded. Adjustments included a modified shield, segment erecting trailing can, and improved hydraulics and electrical systems. The project is unique and highly innovative because the tunnel is being formed using a "ring beam and lagging" system of erecting circular steel rings with timbers between. This has significantly reduced costs and eliminated the need for a large carrier pipe or segments. On completion of each of the three tunnels, two new PE sewer main pipes (600mm & 1200mm) will be run through the tunnels and the void backfilled with "FoamCrete", which is a foamed, lightweight concrete supplied by our wholly owned subsidiary company FoamCrete Ltd.

The difficult ground conditions, which vary between soft squeezing clay to good quality Timaru basalt rock, are being overcome by the combination of traditional tunnelling and the ring beam and lagging system. The two systems together mean that the client's flat grades of up to 1:1800 can be achieved. The mix of basalt, clay and rock has made it slow work at times but the crews have been working 24 hours a day to keep on schedule.

To date, good progress has been achieved and the project is expected to be completed on time in August 2009. Harker are already working on the second tunnel, directly under Westcott and Richmond streets, and the tunnel boring machine will be used again on the third tunnel, from Ashbury Park through to Virtue Avenue early in 2009.

The three tunnels are two and a half metres in diameter, bored at depths of between four metres and 19 metres and are each about 400 metres long.

Project Name:

Main trunk sewer renewal stage 3 - Contract 1753

Client:

Timaru District Council

Pipeline Details:

2.5m diameter, sewer trunk upgrade

Completed:

August 2009