Fig. 129.—Device for Placing Concrete Back Filling for Roof Arch, Capitol Hill Tunnel.
The latter structure was pivoted near the forward end so that it could swing right and left on a circular track under its rear end. It carried a 30-cu. ft. hopper on its forward end, from under which a belt conveyor ascended an incline toward the rear and was carried back into the space behind the roof arch on a cantilever arm. In operating the back-filling machine the material bucket was lifted from the car below, carried back on the trolley beam until over the hopper and then dumped by hand into the hopper. From the hopper the material dropped onto the conveyor belt and was carried back over the arch and dumped in place ready for tamping. The trolley beam of the hoist was so arranged that the hoisting movement was vertical until the bucket hit the trolley and was then up and backward until the stop at the end of the trolley beam was reached. This point was directly over the hopper. Hoisting was done by a Lambert engine, driven by a 15 H.P. electric motor. The conveyor belt was 20 ins. wide and was operated at a speed of 180 ft. per minute by a 7½ H.P. electric motor. The machine required two men to operate and was considered to save the labor of twelve shovelers.
METHOD OF CONSTRUCTING SIDE WALLS IN RELINING THE MULLAN TUNNEL.—The Mullan Tunnel, 3,850 ft. long, on the Northern Pacific Ry., about 20 miles west of Helena, Mont., had its original timber lining replaced in 1894 with a lining consisting of concrete side walls and a brick roof arch. The construction of the old and new linings is shown by Fig. 130. The method of constructing the side walls was as follows:
The original timbering consisted of sets of 12×12-in. posts carrying five segment arches of 12×12-in. timbers joined by ½-in. dowels. For a portion of the lining the posts carried plates on which the arches set; elsewhere the arches rested directly on the post tops. The arches and posts carried 4-in. lagging filled behind with cordwood. The timber lining was removed to make place for the new work in the manner shown by Fig. 130. When there were no plates a 7-ft. section AB was first prepared by removing one post and supporting the undermined arch ribs by struts SS. The timbering in this section was cut out and excavation made for the wall footing. Two temporary posts FF were then set up, fastened by hook bolts L and lagged behind to make the wall form. Several of these 7-ft. sections were cut out at once, each two being separated by a 5-ft. section of timbering. The mortar car shown in Fig. 130 was then run alongside the sections in order and enough 1-3 mortar was run by chute into each to make an 8-in. layer. As the car moved ahead to succeeding sections enough broken stone was shoveled into the last preceding section to take up the mortar. The walls were thus built in 8-in. layers and became hard enough to support the arches in from 10 to 14 days. The arches were then allowed to take footing on the wall, and the posts of the remaining 5-ft. sections were removed and the concrete wall built up as for the 7-ft. sections. Where the posts carried wall plates the struts SS were not needed, the wall plate supporting the undermined post as a beam. English Portland cement was used and the concrete mixture was about 4 parts mortar to 5 parts broken stone—a very rich mixture. The average progress was about 30 ft., or 45 cu. yds. of side wall per working day; the average cost of the walls, including everything, was $8 per cu. yd. of concrete. The brick arch cost $17 per cu. yd. Mr. H. C. Relf is authority for these figures.
Fig. 130.—Sketches Showing Method of Lining Mullan Tunnel.
METHOD AND COST OF LINING A SHORT TUNNEL, PEEKSKILL, N. Y.—The following methods and costs of lining a double track railway tunnel 275 ft. long near Peekskill, N.Y., are given by Mr. Geo. W. Lee. In presenting these data it is important to note that while some of the methods described are applicable to so short a tunnel they could not be used on a long tunnel. Figure 131 is a cross-section of the tunnel showing the lining. The tunnel was through rock, which stood up without timbering, and the rock section was excavated from 6 ins. to 3 ft. outside the lining. A 1-2-4 concrete using crusher run stone below 1 in. in size was used for the lining and portal head wall coping and a 1-3-6 concrete for the portal head walls proper. The cost of the portal head walls is included in the costs given further on.
