To run to spoil is the term applied to such of the material from a cutting which, not being required or utilized in the formation of the line embankments, is removed and tipped into mounds, or spoil-banks, in some one or more convenient sites near the mouth of the cutting. Sometimes the surplus material is disposed of by increasing the width of the embankments.
Material excavated in a tunnel, and hoisted through the shafts to the upper surface, has to be deposited in spoil-banks along the centre line of the tunnel.
To borrow material to form an embankment is the term used when the earthwork filling is not obtained from the cuttings on the line. This borrowing is generally done by excavating a trench on each side of the line, of such width and depth as will supply sufficient material to form the embankment. [Fig. 47] gives an example of an embankment thus made from side cutting. In some cases a piece of high ground adjacent to the embankment can be utilized for obtaining a portion, or even the whole of the filling.
Increased material is sometimes obtained by widening the cutting, or flattening the slopes, or both.
The degree of slope of a railway cutting must be regulated by the nature of the material excavated. A slope of 1½ to 1, which gives for every foot of vertical height a width of one foot 6 inches of horizontal base, as in [Fig. 48], is usually adopted for cuttings in ordinary earth, good clay, sand, or gravel. There are some descriptions of strong clay and marl which will stand at a steeper slope, even at 1 to 1; but, on the other hand, there are some kinds of clay which must ultimately be taken out to 2 to 1, and even 3 to 1.
It frequently occurs that the slopes of a clay cutting, taken out to 1½ to 1, appear to stand well for a time, but after exposure to the frost and rain of one or two seasons, the material becomes loosened, and forms into slipping masses, which slide down on to the line, stopping all traffic, and have to be cleared away before train operations can be resumed.
Cuttings through solid rock may be taken out to a slope of ¼ to 1, as shown in [Fig. 49], provided the material is compact, and there is not too great a dip in the strata or rock-beds. Where the rock-beds lie at a considerable angle, the slope on the high side will have to be made flatter than the slope required on the low side, as shown in [Fig. 50], and great care must be taken to remove from the high side all loose or disconnected pieces of rock which might come away and slide down on to the line.
Strong dry chalk will generally stand at a slope of ⅓, or ½ to 1, but when wet and mixed with flints it will be necessary to increase the slope to not less than ¾ to 1. Where the rock is loose and disintegrated, a slope of not less than ½ or ¾ to 1 will be