Repairs to an old mine shaft hole on State Highway 25 at the north end of Thames township are nearing completion. However, the New Zealand Transport Agency (NZTA) advises that existing traffic detours will remain in place for the next week or so to allow the final stages of the repairs to the hole to be carried out.
Acting NZ Transport Agency State Highway Manager, Michelle Te Wharau, says the NZTA apologises for any inconvenience to motorists, particularly holiday traffic as work crews had been hoping to have the repairs completed before Queens Birthday Weekend.
"Unfortunately the repair work has been particularly challenging around this issue and despite our best efforts, the work could not be completed in time for this long weekend."
"We are doing everything to ensure the historic nature of the shaft is preserved as much as possible but as it is situated in the middle of a state highway, the road has to be reinstated to an appropriate and safe standard," says Mrs Te Wharau.
Mrs Te Wharau says that various options were considered for the repairs, however poor ground conditions around the shaft dictated the type of repair required. "The work has included strengthening the existing stone blockwork on the walls and bridging over the hole with a concrete cover. This has been discussed with both the Historic Places Trust and local mine historians who support these solutions."
Existing detours on adjacent local roads are clearly signposted and will remain in place until the road is re-opened in just over a week's time. "We thank local residents in particular for their tolerance while these detours have been in operation as we are very aware that this has created a temporary increase in traffic volumes past the properties of people living in the area."
With the holiday weekend about to begin, Mrs Te Wharau also says it's important to remember recent NZTA messages around safe driving during the break and as winter sets in properly. "Check that your vehicle and its electrics and tyres are in good condition and working properly before you leave. Always drive to the conditions. Stay alert during the journey - and take a rest break if you're feeling tired."
Mrs Te Wharau says it's also a good idea to plan your journey ahead so you know where delays might occur along the route. The latest travel information is available online at www.highwayinfo.govt.nz(external link) or by phoning the freephone on 0800 4 HIGHWAYS (0800 44 44 49).
Background and further information
The NZTA's attention was first brought to the mine shaft hole after road subsidence was reported on this section of the highway earlier this year. The NZTA's initial investigations in January indicated that the shaft had been back filled and at that time, it seemed some settlement in that fill was the reason why that section of the road had sunk and repairs were put in place accordingly.
However another subsidence incident occurred in April. which prompted the NZTA to excavate much further, revealing the full extent of the old pump shaft. Given that the shaft is an historic underground structure, it was also inspected by archaeologists and mine historians at that time, prior to the second phase of repair works going ahead.
Their investigations suggested that the shaft was part of the first big pump which was used to drain the mines on the Thames Goldfield constructed in 1872, and it is believed to be close to 200m deep. The road became a State highway in the 1960s.
Survey measurements have been taken and other information gathered about the shaft for historic records.
The top of the mine shaft itself is about 6m by 4m and it is lined toward the surface with quarried stone blocks creating a wall around the shaft up to 3m thick.