Earthwork Slips and Subsidences upon Public Works / Their Causes, Prevention, and Reparation

by John Newman

6. Construct the embankments from side cutting, instead of cutting, so that the trenches may catch the snow before it reaches the railway.

7. Make the slope much flatter than its angle of repose.

8. Increase the width of the formation so as to lessen the depth of a drift, and to enable a snow-plough to more readily discharge its excavation.

With regard to the preventive measures enumerated.

No. 1.—As a rule this can only be practised to a limited extent consequent upon traffic requirements and the configuration of the country.

No. 2.—Shelter-galleries are found to be generally effectual, but obviously are expensive; they may, however, be the only means to adopt, as any obstruction to a snow-slip is avoided. The slope of the top of a covered or shelter-gallery should not be steeper than that of the hill, so as to offer no impediment to the free passage of the snow.

No. 3.—Experience has proved that permanent screens are to be preferred to portable shields, and that ultimately they are the more economical. The excavated material, either from a cutting, drains or fence-ditches, is generally used for the earth mounds so as to save expense; their height, which is often from 7 to 10 feet, of course is governed by the greatest depth of the snowfall, degree of exposure and usual direction of storms, wind, and drift. Should these vary much, in an open air line it may be impracticable to entirely shut out or prevent drifts, but the protective works will lessen drifting and may reduce it to manageable proportions.

A simple earth dam is seldom sufficient, owing to the impelling power of the wind upon the snow-flakes and the considerable height at which it acts; therefore, fencing has been fixed in the top of the mound, or trees and shrubs planted, also old sleepers have been successful when simply closely driven into the surface of the original ground. A screen, consisting of one or more rows of trees or shrubs placed at a little distance from the top of the slope of a cutting, is that most generally preferred. It is made either double or single, as may be thought necessary. In Germany, hedges of fir trees similar to Christmas trees have been found to afford excellent protection. In France, pine trees planted upon the cess have effectually prevented serious snowdrifts.

In sloping ground, mounds or dams, screens, plantations of trees and hedges in very exposed places have been insufficient to prevent some drifting and accumulation of snow in a cutting, and a mound or fence has consequently been erected upon the plateau at the top of the hill a sufficiently safe distance from its face that snow-slips, which might be increased into avalanches, were prevented from reaching the slopes or formation. A drain should be cut upon the higher side of such a hill-dam or fence so as to carry away the snow-water upon a thaw, and prevent the earth becoming in an unstable condition.

No. 4.—This system is generally used when an earth mound is also adopted and it has to be deposited from side cutting. The trench, of course, should be on the side of the mound farthest from the main cutting. As a snow-catcher it is successful, especially in shallow embankments, for it not only retains snow that would otherwise heap, but drains an embankment.