. Railroad construction. Theory and practice . V\G. 99.—Standard Timber Box Culvert. C, M. & St. P. Ry. (Feb. 1889.) 189. Stone box culverts. In localities where a good qualityof stone is cheap, stone box culverts are the cheapest form ofpermanent construction for culverts of medium capacity, buttheir use is decreasing owing to the frequent difficulty in obtain-ing really suitable stone within a reasonable distance of theculvert. The clear span of the cover-stones varies from 2 to 4feet. The required thickness of the cover-stones is sometimes § 189. CULVERTS AND MINOR BRIDGES. 207 calculated b
. Railroad construction. Theory and practice . V\G. 99.—Standard Timber Box Culvert. C, M. & St. P. Ry. (Feb. 1889.) 189. Stone box culverts. In localities where a good qualityof stone is cheap, stone box culverts are the cheapest form ofpermanent construction for culverts of medium capacity, buttheir use is decreasing owing to the frequent difficulty in obtain-ing really suitable stone within a reasonable distance of theculvert. The clear span of the cover-stones varies from 2 to 4feet. The required thickness of the cover-stones is sometimes § 189. CULVERTS AND MINOR BRIDGES. 207 calculated by the theory of transverse strains on the basis ofcertain assumptions of loading—as a function of the height ofthe embankment and the unit strength of the stone used. Sucha method is simply another illustration of a class of calculationswhich look very precise and beautiful, but which are worse thanuseless (because misleading) on account of the hopeless uncer-.
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