Southern Relief Wastewater Replacement

Scope

• Installation of 90m Franks PCS PE 1.4m dia. pipe
• Installation of 136m 3.5m deep 150mm PVC gravity pipe
• Dewatering using a combination of wells and well-pointing
• Installation of pre-cast manhole, built in-situ

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Project Description

This complex project involved the replacement of a significantly damaged section of the Southern Relief wastewater trunk main. The Southern Relief is one of the main wastewater conduits which services Christchurch, and this section was located in the residential portion of Worcester Street in close proximity to houses.

We replaced the old concrete culvert with plastic pipe, at a depth of 5.5 metres, but excessive groundwater posed a significant challenge and comprehensive dewatering was required. Given the demanding project environment it was also necessary to grout around pipes to create a ‘dam effect’; and to install both internal and external seals in the existing conduit to stop water tracking, in and around the pipe.

A highlight of our delivery was the innovative methodology we used to construct the new manhole. This was precast, on site, above the ground, before being lowered into position on a concrete slab constructed in the trench. Rails constructed as part of the slab structure enabled the pre-cast manhole to easily slide into place, be tied-in to the pipeline and grouted.

The manhole is an excellent example of our ability to effectively value engineer solutions. We shortened the build programme by one month, saving considerable time and cost; and minimising the period of disruption for local residents.

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