242 



HARBOUR CONSTRUCTION. 



FIG. 



Oregon or Dantzic masts are very suitable for stage piles. 

 They are usually placed with the small ends downwards, and are 

 secured in various ways. 



In the Portland staging they were, during the first period 

 of the work, shod with Mitchell's screws, and screwed into the 

 sea-bed. Afterwards it was found that attaching a large flat 

 stone to the end of the pile, and merely allowing it to rest on 

 the surface, as was done at Alderney, answered equally well and 

 effected a saving in expense. 



Sometimes cast-iron shoes, or sole-plates, are used, varying in 

 size according to the nature of the ground, but 

 generally having an area of from 12 to 16 

 square feet. 



In the Holyhead staging, many of the sup- 

 ports were formed of double baulks, securely 

 bolted together and "fished," half timbers 

 being spiked upon them, as in Fig. 62, so as 

 to split and throw off passing waves. 



Each pile was weighted by means of a box, which was built 

 round the lower part of it and filled with rubble stone. The 

 bases of the piles, instead of being provided with flat stones, 

 as at Alderney and Portland, had wooden 

 cleats bolted to them. They merely rested 

 on the bed of the sea, and, as in the other 

 cases named, were surrounded by rubble as 

 soon as possible after they had been placed 

 in position (see Fig. 60, p. 238). 



Where the sea-bed is of rock, the lower 

 end of the pile is generally hooped with 

 iron, and provided with an iron or steel pin 

 about 1J or 2 inches in diameter, and pro- 

 jecting 12 or 14 inches beyond the bottom of 

 the pile. This pin is inserted into a hole, 

 which must be drilled in the rock to receive 

 it. It acts the part of a dowel, and so holds 

 the pile in position. 



When the surface of the rock is uneven 

 or sloping, a level bed should be dressed for 

 the pile to rest upon ; or, should the rock be 

 of a nature to render this difficult or undesirable, the piles may 

 be furnished with shoes fitting into holes formed for them in 



FIG. 63. 



