Soaring costs of new Clyde-Cromwell road

Press, 10 May 1984, Page 21

Soaring costs of new Clyde-Cromwell road

By

BRUCE THOMPSON,

, for the

Ministry of Works and Development

It was an easy job putting a road between Clyde and Cromwell 100 years ago. Replacing that road today is proving a far more difficult, and expensive, undertaking. The original road winds up the floor of the valley. The new road is being carved halfway up the hillside.

The road which served the area for so long, from horse and buggy through to heavy truck and semitrailer, and through numerous gold rushes, will disappear under Lake Dunstan when the Clyde dam is completed in 1987. The task set the Ministry of Works and Development in Alexandra is to ensure the new road is pushed through the notorious Central Otago schist hillside and completed before that date. The project construction manager, Norm McGeorge, is confident the job will be done within the time limit, but he admits the work is extremely difficult. The most demanding pressure on the engineers is the unstable land that must be dealt with to build the road. Another major pressure is time; investigation work and construction started at virtually the same time.

These problems are reflected in the costs. The 1981 committal estimate for the 51 kilometres of road was $29.3 million. In 1983, the estimate (in 1981 dollar terms) was $46.6 million. In other words, with no account taken for inflation, the estimate for the job has risen 59 per cent. The latest estimate, which does not take inflation into account, is $63 million. Therefore, since the committal estimate in 1981, the cost of the road has risen by $17.3 million because of technical difficulties associated with the geology of the area and by $16.4 million

through inflation. Mr McGeorge believes any further alterations to the reading costs will largely be attributable to inflation rather than problems with the terrain.

The design team has been able to carry out more investigation of the areas where we have yet to start work. That means there will not be so many unknowns.” Unknowns — in this case large silt deposits — pushed the cost of one section of road from a tender price of $6.3 million to a final contract payment expected to be about $11.6 million. The difference was made up by the need to dispose of unsuitable river deposited silts discovered in the construction area, and to replace them with more stable material. This is being achieved by borrowing material adjacent to the site.

“The area where the silt deposits were found should have been a very straightforward piece of road construction. We knew some of these silts were there, but not to the extent found when work actually began,” says Mr McGeorge. “In normal circumstances the silt would not have proved much of a problem. However, we have to take into account the fact that much of the formation will be submerged once the lake is filled. “The silts would have been saturated by the lake which would have caused the road to collapse. Therefore they had to be removed. “We would have known more about the geological structure of the area if time had permitted more investigation, but that was

not the way it was to be. In some cases the silts just did not show up on test drills.” On the section at the south end of the gorge recently opened to traffic the unescalated costs rose from $2.2 million to $6.7 million. This increased cost was due to the need to redesign both cut-and-fill batters as more up-to-date geological data showed the unstable nature of the country, the possible adverse affects of inundation, and wave action. The road work is divided into 18 construction sections. Twenty-two kilometres of road are presently under construction, 10 kilometres are already in use, and 18 kilometres have yet to be touched. By December, a further 15.6 kilometres of road will be in use. To date, three bridges and 14 major culverts have been completed or are under construction. This includes the $2.4 million bridge over the Clutha at Deadman’s Point.

The investigations and practical experience in the area have dictated how to deal with the schist throughout the gorge. “What we are basically doing is a cut-to-fill operation. That means we cut the ridges and fill the hollows. Where the country is unstable we use the road formation to support the existing country,” says Mr McGeorge. The gorge would probably rank as the most difficult reading project in the country. The road is not being cut through solid and stable hillsides. Instead, the sides of the hills are thickly covered with

material that has slipped or moved in the past, and colluvium — rubble and debris deposited by slips.

When the bulldozers start to cut into material like that it can slip both above and below the area being worked. To form the road, and ensure it stays where it is supposed to, more than 10 million cubic metres of rock and overburden will have to be removed and relocated in the gorge.

Mr McGeorge, who worked on the Haast Pass road for 10 years, first for a contractor and then for the Ministry, admits he finds the costs of reading construction today staggering. “We used to talk about two to three hundred thousand dollar jobs as big ones; now we are talking millions.” But the dollars have to be spent. The road through the gorge is a vital link between the lakes district and Cromwell and Alexandra and coastal Otago. The fact that it is such a major route poses just one more difficulty to the new road builders. It also poses a problem for the public. Motorists heading through the gorge must be prepared for stops at least two places for up to 20 minutes a time. “It would be far easier for the Ministry and the contractors if we didn’t have to keep the road open. It would also be cheaper. We wouldn’t have to worry about the road underneath where we are working and could use bigger shots (explosives) and more economic techniques to shift the material.” But Mr McGeorge acknowledges there is no way around that problem. The old road must be kept open and the new road must be built — and it must be built before they finish the Clyde dam and start to fill the lake.