Gladstone Road Subsidence Report Published

Posted by on 25/02/2014


The report on the subsidence that occurred to five properties in Gladstone Road at the end of 2013 has been published on the Hauraki District Council website.

A Technical Working Group made up of representatives from the Hauraki District Council (HDC), Newmont Waihi Gold (NWG), GNS Science and the Ministry of Business Innovation and Employment (MBIE) and Waikato Regional Council (WRC) was established to provide recommendations that would avoid similar situations to the Gladstone Road subsidence in the future.

Their report is to be presented to the HDC at a Council meeting tomorrow (February 26) with a recommendation that the two Councils (HDC and WRC) accept the findings of the TWG.

The summary of the findings of the report indicate that the ‘Newmont Waihi Gold supervised exploration borehole known as CGD008 had not been adequately grouted and allowed the groundwater from the upper level system to drain into the relatively permeable lower quartz andesite material and ultimately into the Martha Pit dewatering facility. This dewatering started at the time the borehole was completed in March 2012.

The dewatering was immediately reflected in the drop of the peizometric levels in the adjacent peizometers (P90 and P92). Unfortunately, the significance of this was not initially realised as there had been no reported settlement associated with the dewatering.’

The summary also suggests that consideration should be given to ascertaining whether there are any enhancements that could be made to permitted activity rule of the Waikato Regional Plan.

The borehole was constructed without resource consent and relied on permitted activity rule of the Waikato Regional Plan instead.

‘The TWG has found that if the conditions attached to this rule had been met, this incident would not have occurred.’

The report summary implies that as a result of lessons learned specific conditions to prevent or minimise the re-occurrence of differential settlement due to dewatering were included in the Correnso consent.

Follow the link to view the full report.