Tracking device

Kiwi ingenuity finds a way to minimise the wear and tear caused by many thousands of feet to a famous scenic walkway.   BY GAVIN RILEY

While large numbers of overseas visitors are important to the well-being of New Zealand’s economy, they can also present a problem.

In recent times, for instance, up to 1000 people a day and around 75,000 a year, many of them tourists, have been walking the famed Tongariro alpine crossing.

This presented the guardian of New Zealand’s great outdoors, the Department of Conservation, with three concerns.

First, the physical wear and tear the walkers were causing to the track. Second, how to maintain a track which could be walked by people of varying athletic ability. Third, how to maintain a walking track in a very harsh alpine environment where the ground structure was largely volcanic rock/ash and mostly devoid of vegetation.

DoC staff had to strike a balance between maintaining the track cost-effectively and within the department’s budget, and taking action which would be compatible with the environment in which the track had to operate.

Even with DoC’s experience, it was a challenge. 

DoC thought it had found the solution in a “Geocell” plastic mat imported from Europe and began to devise laying techniques around the product.

However, in early 2007 an Auckland supplier of injection-moulded plastic products, Jakaar Industries (company slogan, “reinventing plastics”), told DoC it believed it could design a better mat.

In several ways Jakaar was a highly compatible partner for the conservation department: it operated an ISO 9001 quality system combined with a TIMS integrated manufacturing system, had modern European equipment that reduced use of electricity, water and oil, and manufactured many of its products from materials recycled in-house.

The result of Jakaar’s efforts was JakMat Enviro, a 585 x 400 x 43mm ground-stabilisation mat for track and utility area construction. 

Together DoC and Gisborne contractor Logic Forest Solutions developed a system of track reconstruction using the mat, and between December 2007 and mid-February 2008 Logic laid the mat on a 2.5 kilometre section of the Tongariro alpine crossing’s northern circuit.

“Base camp” was at 1400 metres (4600 feet) but the work was carried out up to a height of 1650 metres (5400 feet) – high altitude for a construction job even in summer.

Logic FSL assembled the camp buildings from prefabricated parts helicoptered in and the camp was the eight-strong team’s home for the next 10 weeks. According to Logic FSL director Richard Smith, the accommodation was “pretty comfortable”.

Much less comfortable was the weather. “It was pretty variable in the first stint before Christmas – a lot of rain, wind, sleet, and even snow – but we kept on working,” Smith says.

“We had pretty good weather after that. In fact it was a bit of a killer – full-on heat, no wind, no shade and up to 35 degrees. But we carried on working.”

It was decided that the JakMat could be laid directly onto the existing ground structure, often with minimal preparation. The ground needed to be levelled, though a degree of variation was possible due to the mat’s flexibility.

Once in place the mat was anchored with 10mm x 300mm reinforcing steel pins and they were grouted into the cell they were driven through. The grout used was readily available plasterer’s mortar. There were two pins per two linked mats because of the Tangariro crossing’s extreme conditions.

The JakMat was then filled with aggregate, a GAP20 with high binder clay or similar locally available material, and this was compacted. A further 50mm compacted layer was placed on top of the mat.

It was found preferable to aim for a 2-degree (3-4 percent) slant from the mid-point of the track to the sides to create a positive slope for water run-off.  Timber edging of the track could be used where high water shedding was possible, such as areas where there was sloping ground above the track. In these situations a drain was dug behind the timber, lined with geotextile and filled with rocks.

DoC and Logic FSL acknowledged that this construction method was an evolving process and future variations would be possible, depending on terrain, load requirements and time-span between maintenance. It was recognised there would be cases where laying directly onto existing ground would not be advisable, such as wet areas where a geotextile mat might be needed to reduce fines migration but allow water passage.

In late January this year Logic FSL carried out another contract for DoC using the JakMat, this time on the contractor’s home territory.

Gray’s Bush is a scenic reserve less than 10 kilometres from Gisborne and features an important remnant of the kahikatea (podocarp) forest which once covered the area.  A number of bush tracks can be accessed from the car park and they take 40-60 minutes to walk at a leisurely pace.

Logic FSL had to upgrade 300 metres of a loop track to allow access for wheelchairs and mobility scooters, a task that took six days.

Logic’s Richard Smith says it was decided to use JakMat because it was advantageous to the root system of the predominant kahikatea species.

“We were able to establish a good solid foundation over the roots, which are very old, without any detriment to them. JakMat provides flexibility when the roots grow and expand, as opposed to where there is rigid concrete or an asphalt surface.”

Logic FSL’s construction methods at the flat Gray’s Bush reserve differed from those employed in the rugged alpine territory at Tongariro. After the existing root systems were covered with bidim cloth, the geotextile was overlaid with 20mm of salt-free sand, and the JakMat laid to a width 1600mm and secured with 10mm reinforcing steel pegs.

A cheap but effective aggregate,  a local rotten rock called matokitoki, was used to fill the JakMat cells and a limestone product was then placed as a 20mm top course, with some cement mixed in to create a hard and durable face.

Logic Forest Solutions was formed in 1999 primarily for the provision of harvest planning and road-engineering services to the East Coast forest industry. It diversified into providing civil-contract services for the upgrade and construction of walking tracks for DoC about four years ago.

The company employs six permanent staff during its    September-April construction season and just two staff during winter to provide its forest-engineering services.

Richard Smith, who is from a farming background and has a diploma in agriculture and a certificate in forestry, agrees that DoC and Logic FSL may still be on a learning curve in the use of JakMats in track upgrades. However, DoC appears pleased with the results so far.

DoC’s Turangi/Taupo contracts supervisor, John Wilton, says that although the Tongariro upgrade involved an advanced technical design compared with previous types of track constructed within the national park, the work was completed in very quick time.

And DoC’s Gisborne area programme manager, Jamie Quick, says Logic FSL has displayed a very thorough safety process and an exceptionally good standard of workmanship in successfully completing a number of projects in the area.

Smith says Logic FSL is hoping for more DoC contracts involving JakMats and adds: “We’re based in Gisborne but it doesn’t matter where we travel. We’ve done track upgrades for DoC at Waikaremoana and at Masterton, where we lived in a woolshed and did the Gentle Annie to Rocky Hill track upgrade, using the mat in the construction of box steps.

“There’s nothing similar coming up at the moment, though we’re putting in for quite a few jobs, in Northland, Auckland and Turangi. All DoC work is logistically fairly demanding – dealing with helicopters [bringing in materials], camping out on site, and working in remote areas.

“We’re always looking for new challenges.”