Discovery

Another Boring Tunnel?

Frances Speer

Frances Speer, from Fiordland College, wins $150 courtesy of JADE in this year's School Science Journalism Competition. Frances and the highly commended entries also receive copies of David Burnie's Microlife, from Penguin Books.

Nature doesn't seem to change at Deep Cove. The immense rainfall of 5,290mm annually continues to pour down every other day, the lush rainforest remains in many places still untouched, and the thriving population of sandflies continues to multiply. All this remains, year in, year out. Yet it is almost the opposite at Deep Cove where technology is concerned. Although it is still the last place to look for everyday technology like television, it is a really good place to look for an advanced machine for boring tunnels, aptly named a Tunnel Boring Machine.

This Tunnel Boring Machine (TBM) is furiously at work in the hard rock of a mountain, excavating the Second Manapouri Tailrace Tunnel, or 2MTT. This tunnel, once completed, will carry some of the water that has been used to generate electricity at West Arm Power Station situated on the sunny shore of West Arm, Lake Manapouri.

As you may have guessed from the name of the tunnel, it is not the first to be built at that site. Back in the 1960s the original tunnel was constructed with a similar purpose to the current one -- that is to supply New Zealand's ever-increasing demand for power. Problems with the first tunnel resulted in making a second tunnel to make up for the loss in hydraulic head, which is, in this instance, the difference between the lake level and the water directly downstream of the turbines.

Since the 1960s, methods of constructing tunnels have changed considerably. The original tunnel was formed using drill and blast methods. This created a very rough and uneven tunnel surface that required a lot of concrete (almost 17,640m³) to smooth it out. This tunnel was actually built in two halves, one contractor starting from West Arm and the other from Deep Cove -- when they finally met in October 1968, the two tunnels were only two inches (50.8mm) out of alignment. Not bad, eh!

For the second tunnel, however, hardly any concrete will be needed as the TBM leaves a very smooth surface. The TBM excavates the tunnel by propelling itself forward with hydraulic grippers that it presses against the tunnel walls. It also provides a safe platform for workers to install rock stabilization in the form of rock bolts.

The TBM has also helped to shorten the estimated construction time of the second tunnel. Work on the first tunnel began in early 1964 and breakthrough occurred four years later, in late 1968. In April 1997, the long-awaited work began on the 2MTT and is estimated to only take 18 months, proving that the TBM provides a much quicker method of construction over drill and blast methods.

By using the TBM, they have also helped to improve the conditions the workers on the Second Tailrace tunnel experience. The conditions on the original tunnel were quite rough. Imagine working in the pouring rain, where the previously dry cliff face beside you becomes a river of mud and your clothes are saturated. As they were operating heavy machinery and using explosives in confined spaces, many accidents -- some fatal -- occurred. Lack of knowledge of the conditions in the area caused some accidents that might have been avoided.

The workers lived at Deep Cove at either the campsite or on the hostel ship Wanganella. Everything built on land was done with the intent that they would be demobilized after construction. As Deep Cove is very isolated and doesn't have a nightclub (yet!), the campsite had to provide adequate recreation. Although there was a gymnasium, library and cinema, the favourite recreation was beer drinking -- a massive 546 litres (almost 1,655 stubbies) was guzzled per day during the peak employment period where approximately 600 workers worked on site.

Conditions for the workers on the 2MTT are much better compared to those of the original workers. As the TBM makes less work than was needed for the first tunnel, there is less opportunity for danger, putting the workers at much less of a risk. I asked Ray Hamilton from ECNZ whether the conditions on the 2MTT were, in his view, safer.

"Mining is one of the most dangerous occupations, however I believe FDI -- the contractor for 2MTT -- has provided excellent working conditions for their workers...certainly better than those experienced on the original contract."

Overall the TBM technology has helped construction of the Second Manapouri Tailrace Tunnel in almost every aspect -- from construction to time-saving. Once this tunnel is complete it will add an extra 640 Gigawatthours (GWh) to the national grid, supplying the equivalent of an extra 64,000 New Zealand homes with electricity. So, from the clear, cool air and water of Lake Manapouri to the not-so-clear air of downtown Auckland, all I can say is...Electricity -- I believe in it!

RCD Lessons

Ben Andrew

The illegal introduction of RCD and its resulting outcomes have taught us many valuable lessons. But the future of RCD and biocontrol is still uncertain.

Current research into possible biocontrols such as breeding for resistance and weeding with fungus (for example, the fungus Callego, being used as a mycoherbicide) are future possibilities for biocontrol. Other possibilities are immunosterilisation, like that of flies in the kibbutzes in Israel, which prevents flies from laying eggs, and therefore maggots, on frui; genetically engineering for resistance; the use of pheromones to attract organisms for eradication; and the use of viral proteins to kill pests. Biological control may affect the whole ecology of an environment. The use of any biocontrol is a risk. But this risk may be minimised with proper epidemiology and research. Only the future will tell and teach us what effects RCD will have and hopefully this will be put to good use in future cases.

All for One and One for All

Rewi Stirrat

My oldest sister, Tui, was just an egg at the time when her egg and seven others were taken from Mum's ovaries and mixed with Dad's sperm. Four of the fertilized eggs were put back in Mum and the others had to be frozen because they didn't want Mum to have 8 babies at the same time! Later on they were thawed -- only two of them survived to be put into Mum's uterus and only one turned into a baby.

It took lots of scientists to go through that process. It took people who knew how to remove the eggs and put them back, people who knew how to freeze and thaw the eggs without killing them, people to take blood samples, and people who knew when to do these things.

Australian Kick Boxing Moa?

David Bui

Do not feed the cassowaries! Tourists and local people in Queensland have been warned about this dangerous flightless bird. It only takes one kick from a full-grown cassowary to maim or even kill. These inhabitants of both Papua New Guinea and northern Queensland are becoming increasingly reliant on people for food. And if there is no handouts coming forth, the birds, if forced to, may bash out with the deadly spike-like claws on their feet...

Ben Andrew is in the 7th form at Wakatipu High School in Queenstown.
David Bui is in Year 11 (Form 5) at St Andrews College, Christchurch.
Frances Speer (14) lives in Te Anau and attends Fiordland College, enjoying English, Social Studies and Art.
Rewi Stirrat is nine years old and is home schooled in Wellington.