MT. VICTORIA TUNNEL

Dominion, Volume 23, Issue 7, 3 October 1929, Page 12

MT. VICTORIA TUNNEL

TO BE FINISHED BY JUNE, 1931]

USE OF MODERN METHODS

As the big earthworks develop on both sides of Mount Victoria interest quickens in the great project that is going to bring the eastern suburbs closer to Wellington city by road. As there is a keen desire to see this work prosecuted, there is a noticeable speeding up of activities on the approaches which are being made under the superintendence of the city engineer and at the expense of the city corporation. Both approaches are pretty extensive works, necessitating the shifting of many thousands of tons of virgin country, in this case mostly an admixture of “rotten rock” and clay, with a bit of hard rock here and there. Explosives are being used at both ends, but on the city side only light charges are permissable z owing to the proximity of the houses in Patterson Street. Eighteen Months Time Limit. It will interest many to learn that the time limit fixed by the contract between the city corporation and the Hansford and Mills Construction Company is eighteen months from the time the actual tunnelling work is commenced. That date will not come until early in December, as the gangs on both the eastern and western approaches have enough work ahead of them to keep them going until then. This means that, should the contract be fulfilled to the letter, the tunnel will be finished by June, 1931. Mr. A. F. Downer has been appointed engineer for the big job. Mr. Downer is an expert in tunnel work, having been engineer-in-charge on the Wellington-Tawa Flat tunnel work up till quite recently, and he was instrumental in introducing the very latest tunneling appliances adaptible for such country as exists round about Wellington. Though the company's men will not put a pick into the ground until December, Mr. Downer is now employed all day and every day in making preparation for the work, so that once started it will be continued without a, break until one can see daylight through the hill.

Unusual Method of Piercing.

This will be the first time in New Zealand that so wide a tunnel has been constructed for such a length.. The tunnel is to be 29ft. in breadth, which is quite a fair width for a street in some towns, and this is space enough for two tramway tracks, roadways, and a high-level footpath for pedestrians, below which the space will be reserved for water and electrical mains. With such a width to deal with, methods of tunnelling other than employed on the usual railway tunnel ean be used with , advantage and economy. Block-cutting Method. Mr. Downer has decided to use the blockcutting method in the case of this tunnel. This method entails far less risk than the ordinary open face, gives a permanent dry platform of solid earth for the concrete men to work with their boxing and filling overhead, and finally, when the concrete work is all finished, the block can be removed with greater expedition than it could if worked from a front face. The block of earth to be left in the centre of the tunnel will be 14 feet in breadth and about 10 feet in height, and will be left continuous throughout the tunnel; Then, when the tunnel is concreted in long lines of trucks can be berthed alongside the block, and any number of men can be employed in its removal, whilst if the earth were removed from the faces in the ordinary way the work would be long and tedious, as only a few men could be employed at the one time. This method also provides a safeguard in case of accidents. Accidents occur at times in tunnels, though every care be exercised, but should a fall of earth occur at any point through some misadventure such as an earthquake or a sudden movement of the earth (apart from seismological action), all that can happen is a fall from the roof to the top of the block. True, it might fill in the seven-foot passages on either side, but the chances are that the block would take the main fall and hold it There will be a steel truckway service down the floor level passages on each side of the block, whilst the space between the top of the block and the ceiling of the tunnel will afford plenty of room for the concrete hands to work. Engineers will be greatly interested in the job, as it will' be the first of its kind tackled in this manner in New Zealand.