70 RAILWAY CONSTRUCTION. 



or other of the roads by means of the handle at A. A stout 

 iron pin, or iron clamping-plate, serves to retain the rails in 

 position during the passing of the waggons. In a similar 

 manner, a short rail working on a pin, or pivot, is made to 

 answer the purpose of an ordinary crossing. The rails are laid 

 complete and continuous for the one road, and for the second 

 road the outer rail is laid sufficiently high to cross over the rail 

 of the first road. A piece of rail is then secured by a centre pin, 

 or pivot, to the cross-sleeper, as shown on Fig. 61. This pivoted 

 rail is pulled over into the position shown by the dotted lines, 

 to allow the passage of waggons on the one road, or pulled 

 across to the end of rail at B, for waggons to pass on or off the 

 other road. In the latter case an iron pin or clamp serves to 

 keep the pivoted rail in position. As these service roads are 

 merely laid down on the soft loose material brought forward for 

 filling, they require constant packing and lifting to prevent 

 them working into depressions, which might cause the waggons 

 to leave the rails. 



To indicate the height of the embankment filling, strong 

 stakes or poles must be firmly set in the ground at each chain- 

 peg. On each of these poles two cross-bars must be fixed, the 

 lower one placed to the correct height of the embankment, and 

 the upper one to show the amount allowed for subsidence. The 

 excavated material, as brought from the cuttings, is in a soft, 

 loose condition, and an allowance must be made for its settle- 

 ment, or subsidence, as the embankment becomes consolidated. 

 This allowance will, of course, depend on the height of the 

 embankment and the quality of the material, but for ordinary 

 earth and clay it is customary to allow about one inch to the 

 foot of height, which is equal to about 8 per cent. 



When forming embankments over very side-lying ground, it is 

 necessary to cut steps in the sloping surface on which the filling 

 material has to be placed, as shown in Fig. 62. These steps give 

 a hold to the new earthwork, and check the tendency to slide 

 down the hillside. 



Embankments have frequently to be carried over ground 

 which is low, soft, and wet, but not boggy. If the culverts and 

 drains are sufficiently large, and properly arranged, these places 

 are not likely to cause much future trouble. 



For a thoroughly soft deep bog, however, it is most diffi- 

 cult to make any accurate calculation as to 'the amount of 



