Moore Construction was engaged by Grey District Council (GDC) to undertake geotechnical investigations and construct a new gabion retaining wall to stabilise a slip site and restore the road corridor. Initial site investigations revealed that competent bearing rock was located 6–8m below the western road edge, rendering tall gabion structures unsafe. In response, Moore Construction proposed and implemented a revised foundation design involving 6m deep drilled and grouted RB20 bars in 100mm diameter holes, overlaid with a 2m thick reinforced concrete raft to provide a stable base.
The project included the construction of a 13m long, 4m high gabion wall in four 1m lifts, using hand-placed durable cobble-sized rock to minimise voids. Traffic was managed under a single-lane closure throughout construction. The works also involved installation of a new 1200mm diameter concrete culvert with a WW1350 precast wing wall and thrust blocks, alongside excavation, drainage works, and reconstruction of the road platform.
A dilapidation survey identified damage to an existing 1.2m diameter culvert, which was rectified by installing a 600mm Farmboss pipe inside the damaged culvert, with the annulus grouted to create a cost-effective repair. Other key activities included stabilisation of the downstream slip area with compacted AP65 aggregate, construction of the western concrete foundation pad (6m x 4m x 2.5m) anchored 6m into bedrock, placement of lightly compacted chip aggregate behind the gabion wall, and final surfacing with a 100mm thick emulsion-treated basecourse to reinstate the sealed road surface.
