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track which carries any material coming down the hillside safely over the road. The bents arespaced from 4 to 6 feet apart, according to circumstances. The design shows the structure anchoredto the rock in the side cut with a number of 2-inch rods. Where this is not feasible, appropriatebracing has to be introduced.
The clear space for the track is 15 ft. 9 in. wide and 18 ft. high above top of rails. The prin-cipal timbers used are as follows: main posts, 12 in. X14 in.; side posts, 12 in. X 12 in.; caps, 12 in. X 14in. over main span, and all others 12 in. X 12 in.;braces, 8 in. X 12 in.; roof-plank, 5 in.; side planks,2 in.
Protection-shedfor Mountain-slides, Oregon 6° Cali-fornia Railroad. —A mountain-slide of large pro-portions and under unusual conditions occurred inMarch, 1890, at the north end of tunnel No. 9 on theOregon & California Railroad, connected with theSouthern Pacific Railway system. The methods em-ployed for removing the materials and the construc-tion of a protection-shed to divert earth or rocks,that might come down on the track, were describedand illustrated in a paper prepared by Mr. W. G.Curtis and read before the American Society of Civil Engineers , which paper was published in the Trans-actions of the Society for 1890. In Pig. 112, repro-duced from the publication mentioned, a section isshown of the protection-shed adopted and built afterthe slide had been removed. This died has provedto be sufficiently strong to divert earth and rockswhich have fallen down from the mountain sincethe construction of the shed. The length of the slidemeasured 200 ft. along the track, the height of rockslope is about 100 ft., and the vertical height fromthe grade to the top of the slide about 300 ft. This structure illustrates clearly the application thatis made in practice of the general principles governing the construction of snowsheds on side hills tostructures intended to protect a railroad from mountain-slides or boulders liable to fall down on thetrack.
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Fig. 112.—Cross-section.