Atawhai Drive Road Crossing

This pipeline across State Highway 6 North of Nelson was designed to carry all the runoff from a large development on the hill above, during a 1:100-year rain event.

The pipe chosen was 1350mmm concrete line, with a large concrete outfall structure in the Atawhai Estuary. This outfall structure had a poured insitu headwall and a spill basin below the hightide water level, to disperse the expected large flows during the rain events.

There was a multitude of services to cross, including the main 900mm Sewer out of Nelson, which required auguring in piles to support the pipe and concrete walls underneath to provide trench support for the staff installing the Stormwater line.

A 375mm Asbestos Trunk watermain was also crossed under, which required the cutting in of two new tees, valves and installing a bypass line.

Other services included the main fiber optic cable line for nelson, several 11kv cables, a sewer main and smaller water main. An early 1900s concrete sea wall was also discovered on the road crossing.

All of these services were found within a 24m corridor which meant installing shoring for the Stormwater line was extremely difficult.

The pipeline itself ranged in depth from 3-4m to invert, with a lot of the line encased in concrete to provide support for the services above. A 4m deep manhole was constructed with the inlet pipe at a 99% grade to enable installation up the bank alongside the highway. An elaborate cut was performed on the manhole and pipe with a steel support made in house to hold everything in place during the large-scale concrete pours.

All in all, there was approx. 110m3 of concrete poured on this short section of pipeline. A very challenging project was completed with some minor delays but all services intact and no lost time incidents being a testament to the skilled team involved.