. Canadian engineer. e January 27, igi6. THE CANADIAN ENGINEER 177 borings showing a layer of wet sand. Most of the con-tractors who placed a tender for this work calculated onhaving to install a compressed air plant to facilitate in theexcavation work. This was the reason for vast differencesin prices submitted, the successful bidder being nearly$20,000 less than the second one. The work in the tunnel was carried on from fourshafts, which were situated at locations for hoists were used to operate elevators, whichbrought the excavation from the tunnel to the surface incars, wher
. Canadian engineer. e January 27, igi6. THE CANADIAN ENGINEER 177 borings showing a layer of wet sand. Most of the con-tractors who placed a tender for this work calculated onhaving to install a compressed air plant to facilitate in theexcavation work. This was the reason for vast differencesin prices submitted, the successful bidder being nearly$20,000 less than the second one. The work in the tunnel was carried on from fourshafts, which were situated at locations for hoists were used to operate elevators, whichbrought the excavation from the tunnel to the surface incars, where it was dumped into wagons, taken to BickfordRavine and used for filling-in purposes. The method of excavating was rather unique, havmgnever been tried in Canada before. Contrary to the usualcustom, which is to excavate the full size of bore at once,only the upper half was removed, the lower half or benchbeing left in place until all the excavating and concretingof the arch had been completed in that heading. Tracks. Fig. 8.—Junction Liiaiuher at Lappin Avenue, Section 2. were laid on this bench and the excavated material carriedto the shaft in cars. This bench was also useful as a foun-dation for the concrete forms (Fig. 4). Lengths of 12 to15 ft. were excavated at a time, and after each had beenconcreted another length was taken out, and so on untilthe entire drift was finished in the arch. Then the exca-vating of the invert commenced, this being taken out in•ilternate lengths of 12 to 15 ft. Trestlework was placedunder the tracks as the excavation was removed. Formswere then set and filled to within 1 ft. of the arch con-crete, this space being underpinned with brickwork afterthe concrete had set for at least 48 hours to allow forany shrinkage. When ihese alternate lengths werefinished throughout the drift the intervening portions weretreated in the same way. By this method of placing theinvert the arch was never without support for any greaterlength than 15 ft., for wh
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