Posted by NZTA on 04/05/2012
State Highway 25 at the north end of Thames will remain closed for about four weeks while repairs are completed to cover an old pump shaft.
The NZ Transport Agency reports that the recent subsidence of the road was caused by the roof of an old pump shaft collapsing. Extensive excavation has revealed the full extent of this historic underground structure, which has been inspected by archaeologists and mine historians.
The shaft was part of the first big pump which was used to drain the mines on the Thames goldfield constructed in 1872, and is believed to be close to 200m deep. Survey measurements have been taken and other information gathered about the shaft for historic records. The hole which needs to be repaired is about 6m by 4m, and is lined with quarried stone blocks creating a wall around the shaft up to 3m thick.
NZ Transport Agency Waikato State Highway Manager Kaye Clark says it is thought that the hole was covered by timber and the road built over it by the local Council at that time. The road became a State highway in the 1960s.
“Over time the timber in the shaft has decayed. The repair has been a challenge to our engineers who needed to design a method to span the hole without putting too much load on the walls. To repair the hole we will brace the inside walls of the shaft and build a reinforced concrete cover to bridge the hole and then rebuild the road,” she says.
The works to reinstate the highway are expected to take about 4 weeks to complete. Traffic will continue to be diverted away from this section of highway through adjacent local roads until the road is back in operation.
“We recognise that this has caused some concern to local residents and in particular Moanataiari School. We apologise for the inconvenience and will do what we can to make the detour route as safe as possible,” Mrs Clark says. Mrs Clark notes with concern that traffic has occasionally been misdirected to other roads in the area rather than the correct detour, because signage has been tampered with creating confusion to motorists. "This is a safety concern and we would ask that people respect the NZTA's warning and directional signs at any worksite. Interfering with them creates a safety risk and it is an offence to tamper with this signage. We are working with Police to ensure the worksite remains safe and a security guard has also been employed to keep watch on the site and the detour routes. This extra step will support general road safety measures in the area and also help protect local residents so they are inconvenienced by this unwelcome behaviour. "
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