FAULTY TUNNELS

New Zealand Herald, Volume 81, Issue 24970, 12 August 1944, Page 9

FAULTY TUNNELS

INQUIRY INTO CAUSES

design and work COMMISSION'S FINDINGS ( P v ) WELLINGTON, Friday Cracks and defects in the Fordell and Turnkina tunnels, which the Minister 0 f Works. Mr Seniple. stated Inst March ! would cost about U150,000 to remedy, j were investigated by a Commission of Inquiry, which has reported its findings to the House of Representatives. Causes of failure are found to bo twofold : —(I) Strength provided by the (jpsign, us interpreted from the drawjn,rS, was inadequate; (2) workmanship was in some major respects faulty, and greatly reduced the strength which would otherwise have boon available. There were no records of preliminary investigations as to the class of country likely to be found. Hard rock was apparently anticipated. Among first plant stiptilied was full equipment of rock drills- "It is difficult to determine how such nu assumption was justified—why no real preliminary investigation was carried out." states the commission. No Specifications Discussing design, the report ■ finds that American practice was followed in both tunnels—vertical sidownlls, rather than arched, a departure front New Zealand standard practice. There was nothing inherently unsafe, provided wall thickness was adequate. It was easier to timber and offered better facilities for mechanisation of work. The design had been used previously in hard-rock tunnels on the Waikokopu-Gisborne line. There sidewalls wore lined with pumped 1 concrete, generally 19in thick, against solid ground. Under these conditions the design was entirely successful. Initial instructions from head office to district engineers wore largely verbal —given during visits of an inspecting engineer, "no record on the files of the official number of the plan to bo used, jior of any specification having been sent." A significant statement by the commission is: "Kxcept that the only plan available was that prepared for the Gislwrne tunnels, it is really only surmise that this was the one adopted." Plans were, however, provided with full particulars of the types of timbering, and of steel profiling for concrete work. Apparently from these the tunnels were built, "but without any directing or explanatory specification." Wall Thickness Insufficient The report suggests that when considerable pressure was indicated in the Fordell tunnel that should have made it plain that the intended wall thickness was insufficient, especially realising the vibration inevitable during the passage of a heavy locomotive followed by B long train. Another factor which should have drawn attention to this matter was that shortly after the commencement of tunnelling the ground was found to be so loose that anchors could not be provided for the mechanical scrapers, which were therefore abandoned, and all spoil handshove I led. The work, states the report, was done by co-operative contractors, four parties being always at work, each having a head man " in charge of operations. These head men and a sufficient number of each party were tunnellers with considerable experience in the construction of tunnels of the old standard design. None of them, however, had been engaged on tunnels built to the design adopted. The Public Works overseers and supervising foremen were experienced miners, and, except for one foreman, had had considerable experience | in constructing tunnels to the old standi ard design. "Disgraceful Conditions"

Neither workmen nor supervisors tvere, therefore, by experience, familiar with any pitfalls attaching to_ the new type of" work. At the same time, continues the report, their experience was quite adequate to teach them what had to be done to ensure a good sound job. The absence of any specification and of any written instructions unfortunately made it impossible to know whether they did all that was asked, and, indeed, whether the supervisors themselves knew definitely what to demand.

"fn spite, however, of all Wiese facts and happenings," adds the report, "it is held that the presumable general expert knowledge of essential requirements on the part of engineering and supervisory staff should have prevented some of the disgraceful conditions found, even although among those assumed to know there appears to have been much difference of opinion as to correct, practice, and the absence of a specification is, therefore, all the more regrettable." Defects in Workmanship

Discussing the workmanship in the tunnel, the report says that work done with the concrete gun was, at least ailing the arch, much superior to where handwork was adopted, and it was unfortunate that for no apparently good reason the concrete gun method was not followed throughout. The main delects in workmanship were in the failure to fill the arch so as to catch the country. Had the arch work been properly executed the structure must have stood much better and some of the cracking might not have resulted, or might not Lave become evident so soon. All those directly concerned with the construction of the tunnels appeared from the evidence obtained, and the frankness with which it was given, to have been keen both to push the work along and also to ensure its being a good job within the limits of their instructions and knowledge, although in some respects, stales the commission, results have shown they failed to do some of the things which were essential. "At the same time it cannot be properly said that, any evidence has been shown of deliberate neglect on the part of the Public Works construction staff, most of whom were grossly overworked."

Inadequate Supervision The commission goes into details concerning the system obtaining in the department, lack of records ol diseussions and decisions, responsibility tor final decisions, delegation ol authority, tli> share of responsibility 'Mtried by the inspecting engineer, and the nature of th country. "The surprising factor was, although quite early in construction it was obvious to all concerned that the country was quite different from that stated to be expected, no one considered it necessary to make any Provision for additional strength." The commissi in found that the work *'as not adequately supervised. Instances are given. For six mouths there was no overseer on the Turakinn tunnel, "part of his duties, in theory. being carried out by an engineer's assistant who had no tunnelling experience. 'I he effect of lack of engineering assistance Was that the assistant engineer in charge had too much detail to do, with the result that lie was unable to give detailed supervision to the actual tunnel work. Things happened of which he was unaware. Although the main responsibility must, be allocated to the district engineer, the bead office cannot escape its share for seeing that the supervisory staff was adequate." Degree of Culpability The degree of personal culpability attaching to officers ol the department 15 then assessed by the commission. Bad workmanship on the part of the workers was disclosed in the placing of concrete in the crown of the arch in portions ol jhe job. In some places concrete was less than half the required thickness. However, difficulties attaching to the class of timbering ordered should not be overlooked. There was no evidence of deliberate slumming, but indications "that the tunnellers merely carried out what was required of them, although ill Settle instances this was against their experienced judgment. This course was lot justifiable." ,Ihe Prime Minister, Mr said in the House that he wotdd be wi 11- , J&K to make a special opportunity for ' tocussion.