Retaining Walls in Petone

Petone ground is the softest in the valley

Soft sediments more than 10 metres thick underlie much of Petone and central Lower Hutt. That is a very different founding condition to the dense Waiwhetu gravels further up the valley, and it changes footing design on anything structural.

The southwest end of the valley, from Petone through to Seaview, has also been assessed as having high liquefaction potential. That does not stop you building a wall. It does mean a flexible wall type is often the smarter choice, and that anything engineered needs a design written for this ground rather than lifted off a standard detail.

Narrow villa sections decide the wall type

Petone was the first European settlement site in the Wellington region, back in 1840, and the street grid around Jackson Street still reflects that age. Sections are long and narrow, houses sit close to the boundary, and there is often barely a metre between the villa wall and the fence line.

A 200mm timber pole plus rails plus 300mm of drainage metal eats most of that. Steel post and concrete sleeper walls solve it, because the post is around 100mm wide and the panels are thin. On the tightest jobs down here it is the deciding factor.

Salt air and where the water goes

The beach is a few streets from most of Petone. On gabion work we specify PVC coated mesh rather than bare galvanised, and we use hot dip galvanised or stainless fixings throughout, because salt air works on cheap fixings quickly.

Drainage discharge takes real planning here. The land is flat, the water table is close to the surface, and there is almost no fall to work with. We sort the outlet before anything gets dug, and often that means connecting to stormwater rather than discharging to daylight.