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Retaining wall strengthening under SH1 with pre-fabricated double corrosion protection ground anchors

Project Overview


Because of the 2016 7.8 magnitude Kaikoura Earthquake, many sections of SH1 to the north of Kaikoura were realigned, protected from geohazards, or for structures like the Blue Duck retaining wall, needed remedial strengthening. This section of road curves tightly around the coast with steep cliffs on the other side leaving the only option to construct a piled retaining wall with anchors to strengthen and underpin the road sitting over fractured rock and fill.

During the planning and construction numerous program critical, commercial, and engineering risks were identified or encountered by the delivery team. Geovert added value at this point by driving
practicable solutions and with proactive plans in place to mitigate potential delays from the key challenges to the project.

Geovert Solution


The free and bonded length in rock were determined at the completion of the drilling with the anchors then fabricated onsite and allowed to cure before moving in cradles due to the length. Due to the substantial grout loss initially encountered, we moved from temporary to permanent 180mm casing systems to 10.5m deep, with some bores still requiring extensive pre-grouting and re-drilling to pass water tests before installing and grouting the anchors.


Concrete trucks were used to supply flow-able fill and a bentonite slurry was also used for larger voids. The fabrication of the anchors was on a scaffold frame to enable pre-grouting of the 18.5m long B40 Freyssinet bar anchors. Installation was completed using specially manufactured cradles suspended from a crane over the edge of the road to prevent cracking. Each of the anchors were tested to 913kN before being locked off for the capping beams to be poured and the SH1 to be reopened to two lanes.

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