Top Retaining Walls Lower Hutt builds gabion retaining walls across Lower Hutt. A gabion is a wire basket packed tight with rock, and a row of them works as a gravity wall. The face is permeable, so water runs through instead of banking up behind it, and that single property removes the most common cause of wall failure in this valley.
Every other wall type fights water. You build a drainage layer, run a coil, wrap it in geotextile and hope nobody blocks the outlet in fifteen years. A gabion wall has no solid back face for water to push against. Rain arrives at the rock, moves through the voids and comes out the front.
We still lay geotextile behind a gabion, because we do not want fine soil washing into the rock over the years. The wall itself is not depending on that system the way a timber or block wall does.
| Baskets | Galvanised or PVC coated welded mesh |
|---|---|
| Rock | Angular greywacke, commonly 100mm to 200mm |
| Source | Wellington region quarries, short cartage to the valley |
| Facing | Visible faces hand packed, centres machine filled |
| Drainage | Permeable by design, plus geotextile behind to stop silt |
| Movement | Flexes rather than cracks, suits soft and fault line ground |
| Harbour sites | PVC coated mesh recommended near Petone and the bays |
Gabion rock has to be angular and hard so the pieces lock against each other. The Wellington region is founded on greywacke, a hard grey sandstone from the Torlesse rocks, and the hills on both sides of the Hutt Valley are made of it. Quarried greywacke is angular, it breaks with flat faces and it is a short cartage run to any site in the city.
We hand pack the visible faces so the rock sits flat and tight with no gaps showing, then machine fill the middle. A hand faced gabion looks completely different to one that was tipped full, and the difference is labour rather than materials.
A gabion wall is flexible. If the ground settles a little the baskets deform slightly and carry on holding. A rigid wall in the same spot cracks. The Wellington Fault runs along the western edge of this valley, and the ground from Petone through to Seaview has been rated as having high liquefaction potential, so tolerance for movement is not a theoretical benefit here.
The wire decides the life of the wall. We use galvanised or PVC coated mesh, and anywhere near the harbour, which means Petone, Seaview, Point Howard, Days Bay and Eastbourne, the PVC coating is worth the extra because salt air attacks bare galvanising.
Moss and small plants colonise the face, especially on the shaded southern side. Most owners like it and it suits a bush edge boundary. If you would rather it stayed clean, keep the face in sun and clear it occasionally.
You can also plant into the top course or run a soil filled cell along the front. Gabions take that well because they drain so freely.
Every wall we build gets drainage. At least 300mm of clean free draining metal, a perforated coil at the base running to a real outlet, and geotextile over the top so silt cannot block it. It is not an optional line on our quotes.
The wall drains through the face, so water pressure is not the problem it is with other walls. We still lay geotextile behind to stop fine soil washing into the rock over time.
The rock lasts indefinitely. The wire is the limiting factor, so mesh coating decides the life. PVC coated outlasts bare galvanised, particularly in salt air along the harbour.
Around New Zealand they usually land in a similar band per lineal metre. Hand packing the faces is the main cost, so a long straight wall prices better per metre than a short fiddly one.
Our old wall was rotten right through and leaning into the neighbour's place. They pulled the lot out, put proper drainage behind the new one and had it finished in three days. Swept the site clean every afternoon before they left too. Tidiest crew we have ever had here by a long way.
They sorted the consent, which was the bit I was dreading. Dealt with the council so I never had to, and kept me in the loop the whole way through. The driveway sits right above it and has not shifted a millimetre.
Steep section, shocking access, and they still made it look easy. They suggested two smaller walls instead of one big one, which saved us thousands in engineering fees. The terrace in between is now my favourite part of the whole garden.
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