The Challenge:

Heavy rain destabilised a steep clay bank that slipped onto the southern end of the Esplanade at St Clair in Dunedin. The potential for further slips was high and the slip proximity posed an immediate threat to the adjacent house. The proximity to the neighbouring property also made access challenging, ruling out an anchored wall as an option for the lower section.

The Solution:

HGM constructed a 2.5-3 m high anchored timber pole retaining wall and a 2.5m Steel UC retaining wall with a Cirtex T-Recs and Promat matted slope secured with 60 Platipus earth anchors.

Minova Weldgrip self drilling anchors were used to tie back the new timber and pile retaining wall. A sacrificial test anchor was installed to provide onsite load values to allow the design to be optimised. The pull test results greatly exceeded expectations due to installation using the simultaneous drill and grout method. This allowed the proposed anchor lengths to be reduced from 12 metres long to 8 metres and provided a saving in both materials and job time. 

On the lower section, a Cirtex T-Recs and Promat matted slope secured with 60 Platipus earth anchors was installed over the exposed clay face finished with soil and hydro seed. The anchors were attached to the tantalised piles with stainless steel end plate and grease filled end caps to prevent corrosion in the coastal conditions.

The simplicity of the self drilling anchor system meant that it was a much more cost effective installment process than traditional cased hole anchoring. The solution was implemented smoothly without problems and the project was delivered on time and budget.