International Correspondence Schools · Scranton, Pa. : The Colliery engineer co. · leaf 594
on, which can easily be renewed. 1744. Sub-sills, or mud-sills, are blocks of timberplaced under the main sills to raise them above the groundand so prevent decay. Some recommend planks o or 4 inchesin thickness, but 12-inch by 12-inch timber is far better,and the additional cost is trifling… … Fig. 564. driven as shown at a, a, in Fig. 504, will serve for afastening. 1745. A grillage of timber may be employed as afoundation when the trestle crosses a marsh extending to agreat depth, but covered by a layer of earth possessing con-siderable supporting power. vSuch marshes are frequentin…
Railroad engineering
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