Cases will arise where it will be necessary to make a shallow cutting through boggy peaty ground. If the boggy material be very soft, and its thickness from the formation level to the solid ground below be not great, it may be advisable to remove this extra thickness down to the hard lower bed, and fill in up to formation level with strong material. If, however, the bog or peat be too thick to justify its entire removal, it should be excavated say down to two feet below formation level, and a thick layer of branches of trees and strong brushwood closely laid and packed the full width of the road-bed. On this preparatory foundation must be placed good clean ballast to carry the permanent way. Two or three extra sleepers should be allowed to the rail length, and in some instances it will be necessary to introduce two, or even four, rows of strong longitudinal timbers—half balks—under the transverse sleepers. The object of all this extra timber is to obtain a large increase of bearing area on the soft yielding surface of the boggy material. Notwithstanding these special precautions, the trackway will sink down a little during the passage of an engine or train, but will generally return to its former level. Good side drains or water-tables should be formed at each side of the cutting to take away all rain and surface water.
In all cuttings it is desirable to have the line of formation on a slight gradient, sufficient to carry away all rain water or spring
water which may be collected in the water-tables; but more particularly so is this necessary in a rock cutting, where the material, being non-absorbent as compared with earth or gravel, requires that all drainage must be carried away to the mouth of the cutting.
In carrying out railway embankments and road approaches, it is usual to form the sides to a slope of 1½ to 1, as shown on [Fig. 56]. Occasionally the cuttings produce material which might stand at a rather steeper slope, but considering the effects which might afterwards be produced by heavy rains falling on the sides, it is more prudent to adopt the flatter slope of 1½ to 1. Some descriptions of clay will not stand at the above slope, but require a slope of 2 to 1, or even 3 to 1.
When proceeding with the earthworks, it is customary to first remove and lay aside a layer, say 9 inches in depth, of soil and earth from the seat of the embankments and top widths of the cuttings, to be used afterwards in soiling the trimmed and finished slopes of the cuttings and embankments. This soil being removed, the actual work of the excavation can be commenced. The working longitudinal section will give all the necessary particulars as to position of the mouths of the cuttings and the depths at the various chain-pegs, and the top widths of the cuttings can be ascertained by calculation, if on even ground, or from the cross-sections if on side-lying ground, according as the material may be earth, clay, or rock.
For facility of carrying on the works, reliable bench marks, or reduced level stations, must be established at convenient distances along the route of the line, and from these and the fixed chain-pegs the correct line of formation level can be checked from time to time as the work proceeds.
For ordinary earth or clay cuttings, the usual tools are picks and iron crow-bars for loosening, or getting the material, and shovels for filling into barrows, carts, or waggons. For heavy earthworks, steam excavators are now largely employed. Great improvements have been made in this class of machinery, in the way of perfecting the method of excavating lifting, and filling the material into the earth-waggons.
In nearly all rock cuttings the greater portion of the material has to be taken out, or loosened, by blasting with gunpowder, dynamite, or other explosive. The number and extent of the charges will depend upon the nature of the rock and its
stratification, and also on its position as regards proximity to buildings or residential property.
Where the rock is loose, or disintegrated, the pieces can generally be readily separated by picks and bars without having to resort to any great extent of blasting.