Transpower contracted Geovert to drill and install the mini piles for the foundation pads which were designed to withstand significant seismic acceleration to protect the newly upgraded transformers.
Drilling was required to be completed to ensure no impact of vibration or dust in the substation with monitoring in place as a further preventive control.
The 178mm diameter mini piles varied in depths from 8m to 19m across the site and required the drilling and installation of permanent steel cased piles which were hammered down through fractured rock, voids, boulders and founded into solid basalt. Large amounts of block fill and flowable grout was pumped into the boreholes & voids for pre-grouting of piles to ensure they remained grout tight in the variable Auckland basalt with some voids up to 5m in height.
Re-drilling of the piles and water tests were completed to ensure the integrity of the piles prior to installing and testing of the double corrosion protected high tensile bar piles. All works were completed to meet the requirements of Transpower with live transformers without impacting the operating substation.