February 2019

Pike River Mine drift re-entry on track

  • By Lee Harris, Pike River Recovery Agency

After eight months of intensive planning and risk assessment, the New Zealand Government Minister Responsible for Pike River Re-entry, the Hon Andrew Little, approved a plan in October 2018 to re-enter the Pike River Mine drift

The Pike River Mine explosion on 19 November 2010 claimed the lives of 29 men and the subsequent explosions resulted in the mine being sealed.

There are two distinct areas of the mine: the mine drift and the mine workings. The drift is a
2.3 km access tunnel from the portal to the workings. The mine workings, where coal was being extracted, contain approximately 4.3 km of tunnels. The workings are the last estimated location of the 29 workers, and are blocked by a large roof fall at the very end of the drift.

Established as a New Zealand government agency on 31 January 2018, Te Kāhui Whakamana Rua Tekau mā Iwa/Pike River Recovery Agency took advice from leading mining, ventilation and geotechnical experts in New Zealand and around the world before submitting their recommendation that re-entry be carried out using the existing drift as a single entry, with suitable best practice controls and a standard ventilation plan.

Figure 1. The 2.3 km access tunnel.

Three options were developed, considered and assessed before the final recommendation was made:

Option A: a 2 m x 2 m short tunnel driven from the surface to intercept with the pit bottom in stone area, or the top end of the drift

Option B: a single-entry through the 30m seal after re-establishing the 170 m seal and systematic recovery of the drift

Option C: a single-entry recovery of the drift, with a 600 mm diameter escape borehole.

A mining team walks the tube bundle system line in the Paparoa Ranges to check the best path for the nitrogen pipelines.

Key elements of all three options included:

  • safe re-entry by personnel in fresh air
  • nitrogen inertisation of mine workings and drift (up to 4 km away from plant location, nitrogen lines to be run through the bush)
  • new boreholes to facilitate inertisation, ventilation, forensic examination, geotechnical assessment and other duties
  • demonstration of control of mine/drift environment prior to personnel re-entering the mine – with a nitrogen plant established on site in October 2018.
  • The following tasks are also consistent in all three options:
  • breach the 30 m seal and re-establish 170 m barrier
  • forensic examination
  • remove existing dewatering infrastructure between
  • 30 m seal and 170 m (where a previous seal was set up – currently has an open door to allow water flow) recovery to within 300m of the rock fall will be in fresh air
  • vehicle access in the tunnel will be required to allow specialist equipment
  • sealing
  • rehabilitation.

All three options for re-entry were technically feasible and all risks for each option were considered. The agency concluded that using single-entry alone (option B) was the least complex and least risky option overall, and the one most likely to achieve the desired outcomes.

In announcing that re-entry would proceed, Minister Little said that he had considered advice from the agency along with independent advice from Rob Fyfe who (as the former chief executive of Air New Zealand) has been a corporate leader in a safety sensitive industry and has his own engineering experience.

The advice from the agency and from Rob Fyfe to the Minister is available on the agency website at www.pikeriverrecovery.govt.nz.

Pike River Recovery Agency mine site-based roles

The Agency is looking for two new people for mine site-based roles. More information can be found here: https://www.pikeriverrecovery.govt.nz/news/health-and-safety-coordinator-and-recordsinformation-coordinator-sought/ 

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