Engineer Says Concrete Not Kaimai Safety Issue

Press, Volume CIX, Issue 32313, 3 June 1970, Page 30

Engineer Says Concrete Not Kaimai Safety Issue

INew Zealand Press Association)

HAMILTON, June 2. A concrete shell would not have created a haven of safety for workmen in the Kaimai Tunnel, a tunnelling consultant told the Commission of Inquiry yesterday.

Mr G. J. Hallewell, consultant engineer to the Ministry of Works on the project, said this in evidence before the three-man commission sitting in the Maori Land Court in Hamilton.

Mr Hallewell said a concrete shell would have had no effect on the men’s safety because the flow of material had run through the tunnel.

Early last week, the tunnel overseer, Mr B. A. Neely, told the commission hd believed a concrete shell would have saved the Lives of the men killed in the collapse on February 24. The commission inquiring into the disaster comprises Messrs A. W. Yortt (chairman), K. E. Andrews and J. F. Handcock. Mr J. D. Bathgate is appearing for the Public Service Association, Mr J. Rabone for the Ministry of Works, Mr N. E. Smith for the New Zealand Workers’ Union, and Mr V. R. Jamieson for the Mines Department

Cross-examining Mr Hallewell, Mr Smith said that if there had been a chance that bringing the concreting right up behind the workers might provide safety, then it should have been done. Gone Too Far Mr Hallewell said that in most soft-ground tunnels a concrete lining was kept close behind the face. “It is usually a normal requirement, but is not in steelsupported tunnels,” he said. Looking back now he felt the tunnellers had gone too far and too quickly, failing to make the timber good behind them. “It would have been a lot safer if they had gone more slowly, securing everything,” he said.

Mr Hallewell, replying to Mr Smith, said that looking at the section of tunnel being done now everyone would be happier with concrete close behind them. Mr Smith: And safer? Mr Hallewell: Maybe. Mr Hallewell said in a statement that the section of the tunnel which collapsed in November, 1969, was being advanced without adequate support He had come to this

conclusion after further investigation and by listening to the evidence of the inquiry. Mr Hallewell said he considered that the spiles, described as long needles, pushed ahead of the tunnel to provide overhead protection, had been pushed ahead without adequate support. In earlier evidence he said that the original system of tunnelling proposed for the deviation could have been persisted with, and if so would have provided better protection than the eventual timber sets were able to provide.

Mr Hallewell said his initial plan for the tunnelling was one where steel ribs would provide the final support for the surrounding country. “The original idea was to construct a single bottom

heading and later enlarge it,” he said. This would be accompanied by spiles being driven in ahead, providing a fairly complete roof. Giving his reasons for the failure of the plan, Mr Halle-

well said the system had been designed with very little tolerance. “This was done deliberately," he said. “The loads on the tunnel were such

that everything had to go together correctly.” He thought that one of the segments of the tunnel had been taken too far forward without any support. Early in 1969 it had been decided to proceed with a bottom heading, replacing the two side headings previously agreed on, but at that time the conception was not terribly firm.

Difficulty had been experienced in obtaining steel ribbings and the beginning of tunnel enlargements had been delayed several months until October, 1969.

Early in December he had received a call from Mr Bennion, the resident engineer on the project, who said they had been having difficulties in advancing the spiles. He had visited the site, found conditions very difficult and had advised tunnelling to be made secure for the Christmas shut-down rather than advance further. About December 19 he had proposed a method, based on an Austrian process, of propping tunnel timbers from a concrete invert, and in January this method had been commenced. Not Finn The method involved driving five headings and using more spiles. > On January 20, his next visit, the top heading had gone well ahead of the difficult area and things were looking much better. On his last visit before the cave-in the tunnel between 90 feet and 120 feet had opened 'out and it was proposed to drive in either direction. He said he had no reason to believe his spile system would not have worked if conditions had been more favourable at the start of tunnelling. Certainly it could have been persisted with, and if so would have provided better protection than the eventual timber sets were able to provide. ‘•But practical men said this would not be so and I cannot contradict them as the vital phases occurred when I was absent,” he said. “The timber system evolved on the Austrian idea, so far as 1 can judge, worked perfectly so far as it was taken but unfortunately it was not completed sufficiently close to the face, and the heading was pushed too far ahead of the : steel. “A more cautious approach :here would probably have I avoided the fall, or at least minimised it considerably.” ! Under cross-examination by

Mr Rabone, Mr Hallewell said he regarded the tunnel as a “throwback to the 19205, in the nature of the country, the tunnel size, and the methods we had to use.” He said the bottom heading

approach had been a common method in the 1920s —“quite the most common way of doing it” From his observations on

visits to the site the bottom heading had been standing up well. “The only weight was in the portal section,” he said. "Elsewhere there was very little. There was no cause anywhere for alarm." Mr Smith: When you referred to a throwback to the 20s did you mean your methods were somewhat archaic? Mr Hallewell: Not at all.

A tunnel of this nature and in this type of material has not been attempted in New Zealand in the last 30 to 40 years. Modern-day methods don’t suit this sort of coun-

try. He denied an accusation by Mr Smith that the Ministry of Works did not have engineers experienced enough to tackle the tunnel project. “I have tunnelled in worse ground,” Mr Hallewell said. “One tunnel is not exactly the same as the next. 1 consider the project within my experience.” He told Mr Smith he considered the methods used were as up to date as anyone could use in the circumstances. Mr Smith: In other words, with equipment of the 1970 s

you were using methods of the 19205? Mr Hallewell: Yes. No Other Way He said that in the last few years the way to deal with this type of ground was to dodge it Generally it was possible to avoid country like this.

“It would have been a good thing if we could have avoided these hills,” be said. “There was, however, no other way.” Mr Smith: Don’t you consider it would have been prudent to have inquired overseas about this type of tunnelling in this type of ground?

Mr Hallewell: No. Not if it has not been done overseas recently.

Mr Hallewell, questioned on the availability and experience of Ministry of Works engineers on tunnelling, said he supposed he bad been consulted. “In tunnelling you lean heavily on experience,” he* said. “It is definitely poor coun try- It is soft-ground tunnelling and this is almost a lost art round the world.”

Mr Hallewell said he did not agree with evidence from Messrs Bennion and Newman (engineers on the project) that his construction methods had caused the initial subsi dence.

“All 1 can say is that at the time of the subsidence my system wasn’t being properly carried out,” he said. He did not think there would have been any defects in his scheme if it had been properly implemented. “The roof would have been completed and it would have been okay,” he said. The first notice he had received of his scheme being abandoned was from Mr Bennion early in December. Mr Hallewell agreed with Mr Smith that the change from steel ribs to timber sets was rather drastic. “I was told the decision to change was made by the resident engineer (Mr Bennion).” he said. “I consider it within his rights but 1 think he should have conferred and had agreement before he went ahead.” Main Worry His main worry after his scheme had been abandoned, wat, that a total collapse might follow over the Christmas period when the project work stopped. Referring to an earlier statement made by Mr Bennion, that he had misjudged the country, Mr Hallewell said he had seen the worst conditions of the area. “I don’t think there was any misjudgment,” he said. “I consider my scheme O.K. 1 have not heard anything to change my mind.” He thought the major collapse on February 24 had been a two-stage thing. Material coming through an opening above the first cap had started the initial slide which had blocked the entrance to the tunnel. “This possibly gave an area into which another slide would come,” he said. “It came through the same opening, swept away support legs and, being silty and very wet, it liquified and ran up the tunnel, pushing over supports and steel sets.” Mr Hallewell attributed the collapse to a combination of poling-back and working too large a face in the quality of material in the cave-in area.

Chathams Convoy.— A three-ship convoy left Lyttelton for crayfishing in the Chathams on Sunday. It comprised the Marilyn H., Stella Maria and Mystery Girl. A six-ship convoy is to leave Lyttelton for the Chathams next week-end.