Stockton Mine Coal Handling And Processing Plant

Mother Nature throws up plenty of issues on this project. Article supplied coutesy of Jenny Bain. Rooflink

Stockton Mine in Buller, New Zealand’s largest opencast coal mining operation, has been a site of coal extraction since the late 1870s. Located high on a plateau north of Westport, 800m above sea level, the mine is operated by Stockton Alliance for Solid Energy New Zealand Ltd, delivering high-quality steelmaking coal for export.

Solid Energy has recently built a new coal handling and processing plant to handle the substantial amount of coal mined that could not be sold owing to being mixed with rock or other materials. The new plant means Stockton can add at least 500,000 tonnes a year to the mine’s output over the next 20 years.

RANZ member Wayman Roofing Services Ltd (WRS), Christchurch installed the roofing and cladding on the $124 million plant, construction of which involved more than 250,000 hours of work over 500 days employing more than 750 people over this period with no lost-time injuries. Paul Wayman will attest to the effectiveness of the extremely robust health and safety environment adopted and its success on this contract.


The new plant was designed by Downer Engineering and built by Nelson firm Brightwater Engineering (BWE). WRS has enjoyed a working relationship with BWE over many years, having worked on projects in the Nelson area particularly at Nelson Pine Industries. The company has also been involved on several mining projects including the processing plants at Spring Creek Mine, north of Greymouth, (another Solid Energy project) and the Globe Hill Mine for Oceana Gold near Reefton.

Early in 2008 BWE approached WRS about being named as their preferred roofing and cladding contractor in their bid to Solid Energy for the new processing plant at Stockton Mine. There were a number of design and construction issues on this site including those from mother nature: high rainfall (up to 600mm per month), low temperatures (between 0 degrees and 15 degrees C dropping to minus 5 degrees C in winter), fog (which often obscures visibility to the point where earthmoving operations at the mine are suspended to ensure operator safety) and the area is also prone to earthquakes and very high wind speeds.


WRS’s budget pricing began in August 2008 and before construction drawings were finalised, BWE talked to Dimond about the most appropriate products for this harsh environment. The structural steel specification required the material to be designed for a permissible service temperature of minus 10 degrees C to ensure suppression of brittle fracture. Earthquake loading was the critical design load for the coal processing plant and was approximately three times greater than that for a similar structure in Australia.

Dimond recommended double sided ZRX V Rib profiled cladding and Durolite 3600gm Webglass for the roofing and cladding. High altitude, steep topography and proximity to the coast and very severe climate meant designing for wind speeds in excess of 230km/h.

Prior to any work commencing BWE built 17 conveyor and plough units in their Richmond (Nelson) yard and Nelson Marlborough Roofing Ltd clad these prior to delivery. Once delivered to the Stockton site they
were assembled in units of three by WRS and then lifted into place on trestles with all flashings and junctions completed once they were in place by WRS.

Says Paul Wayman: “Because the construction site was in the middle of a working mine and at an altitude of 3000 feet we had our own issues to deal with in terms of rigid health and safety requirements and the extremes in climatic conditions.

“We also had to deal with how to manage and safely install both the roofing and the wall cladding as the height to the ridge from the ground was approximately 25m”.

Wall cladding

Clean water is at a premium on the construction site and every effort is made to collect rain water. Therefore the wall cladding was started at the top with a lap in the sheets on the outside of the top sheets facing upwards in order to catch the water shed off the walls which was diverted to the inside for collection. At the base of the walls and all the way round the perimeter WRS installed large catch flashings to divert the rest of the water -shed from below the tap line.

The longest wall sheets were around 13m and we had to devise an approved lifting system to crane the sheets into place, said Paul. This consisted of a profiled cradle into which the V rib was clamped end on and a pair of lifting strops and yoke was attached to that. This system enabled the sheets to be lifted individually to a vertical position by crane and then installed with the use of the crane and large boom lifts.

There was a WRS crew of up to five on the job at any one time – this was the total required due to the limited work faces made available because of the complex nature of the construction but it also meant less exposure to periods of unproductive downtime due to the weather.

Health and safety

Anyone with doubts that a more prescriptive health and safety environment is unwarranted and unnecessary would have those myths dispelled had they witnessed
how successful it was on the mine project, says Paul. The success included the fact that.

  • Everyone was subject to it – no excuses.
  • Resources were in place to ensure compliance.
  • No expense was spared in providing scaffolding, access equipment and even safety nets where and when required.
  • Brightwater Engineering, Solid Energy and Downer EDI (Solid Energy’s partner in Stockton Alliance, the mine operator) all take health and safety seriously and they ‘walk the talk’.
  • Outlining some of the H & S processes WRS was subject to Paul said a JSA (Job Safety Analysis – a system to identify risks and hazards in a particular task and either mitigate or eliminate them)) was produced for EVERY task on site which all workers had to sign. The JSA had to be modified for any alteration on the work method, or to account for any change that may occur during that work process such as the weather. In addition.
  • A daily Permit for Work was issued after that JSA had been approved, taking into account that no other conflicting work or trade would impinge on the safety of any work being carried out in close proximity. If it did then a permit would not be issued to the other party until that work area was clear.
  • The JSA was attached to the work area in a clear envelope to ensure it could be seen by everyone in the area. Jobs were subject to random inspection by the HSE Officer to make sure that all processes and safety measures were being adhered to.
  • WRS work was shut down if the weather deteriorated or wind speeds increased to the point where it was considered unsafe to continue work (in the case of installing the wall cladding this could be if ANY wind developed).
  • There were also daily pre-start meetings where all trades on site discussed their work processes for that day accompanied by prestart checks on all plant and equipment (including personal transport vans, etc).
  • Every Monday there was also a weekly pre-start meeting for pre-planning for the week and the identification of hazards.

Says Paul Wayman: “Initially It all seemed quite onerous and over- the- top but the boys soon became used to it and the satisfying thing for us was that EVERYONE was exposed to it and HAD to comply. I am an advocate of a more prescriptive system such as we were exposed to at Stockton as it removes any doubt around “all practicable steps”. Solid Energy New Zealand and Brightwater Engineering are prepared to “walk-the-talk” in terms of both enforcement and the associated costs – which is something that we find is seriously lacking in the wider construction industry.

“Overall, taking into account the locality of the site and all that entailed, the logistics surrounding the supply and the installation of the cladding, we are pretty happy with the outcome. There could have been a lot go wrong on a job of this nature.

“It is a testament to our staff, ably supervised by Matt Friedwald and the co-operation of the whole BWE project team on site”.

The ‘zero harm’ target

Says Bryn Somerville, Communications Manager, Solid Energy New Zealand: “At Solid Energy New Zealand we start from a “zero harm” target: no harm to anyone, ever”. That means the risks you’re prepared to accept will be much lower than an employer who might say “well, yes, I’m prepared to take the risk one of my guys might get hurt if we carry on. I think the risk is pretty low so we’ll carry on.” For us, even that small risk might be too much if there’s nothing we can do to mitigate it.