RAILWAY CONSTRUCTION. 61 



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 1 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 1^ 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 

 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 , or to 1, 

 but when wet and mixed with flints it will be necessary to in- 

 crease the slope to not less than f to 1. Where the rock is loose 

 and disintegrated, a slope of not less than \ or | to 1 will be 



