The Challenge:
Recent earthquakes in Christchurch had highlighted the need for earthquake strengthening across the board and Cargills Monument was identified as being at high risk and accordingly given priority for stabilisation work. The limited space around the monument meant that a small highly mobile rig was required at the site. In addition there was very little room for locating the drill at the desired micropile anchor location in the cornerstones next to the vertically rising monument. Large equipment that caused excessive vibration was therefore not suitable.
The Solution:
Self drilling anchor micropiles were chosen as the only practical and cost effective solution to anchor the monument to the existing substrata. The small size of the Pacific Fox drilling attachment allowed it to be mounted on a small 5.5 tonne digger with the drill mast able to be easily manoeuvred around the monument for micropile installation exactly where required. The rotary percussive drill head produced minimum vibration while advancing the self drilling anchor micropile and this posed no threat to monument integrity.
Corner stones were first removed and the flat topped corner blocks then cored to allow the installed anchors to be hidden completely within the structure. Four Minova Weldgrip galvanised R38 Self Drilling Anchor Micropiles each six metres long were installed using Pacific Fox Cub 250 drilling attachment. The angled top corner stones were then repositioned.
The simplicity of the self drilling anchor micropile system meant that it was a much more cost effective implementation than traditional cased hole anchoring. The solution was implemented smoothly and on time and the whole project came in on budget. Spiire were pleased with the final result.
