METHODS OF CONSTRUCTING BREAKWATERS. 243 



the rock. Cast-steel shoes of the pattern shown in Fig. 63, and 

 weighing about a hundredweight each, are suitable in such 

 cases. 



When ground is too soft to admit of piles merely resting 

 upon its surface, they may either be driven or screwed into it 

 until the necessary amount of support has been obtained. 



Lateral support is given to staging by means of chains, which 

 are usually formed of wrought-iron rods, varying from, say, 

 1J" to If" diameter, with eyed ends coupled by side links and 

 bolts. These are attached to the pile-heads by means of eye- 

 bolts, and they are generally made fast either to screw moorings 

 or to anchors weighing about 20 cwt. each, or, where the 

 bottom is of rock, to lewises fixed into it. 



The stays are generally tightened up by means of union 

 screws. 



Although it is often, or indeed generally, necessary to have 

 recourse to stays, they arc objectionable, inasmuch as the waves 

 in a heavy sea take a great hold of them, and cause considerable 

 movement in the staging. For this reason, chains formed of 

 long rods of round iron, coupled together, are preferable to 

 ordinary short link chains. 



When it is necessary to build staging piles into the masonry 

 of a breakwater, as is sometimes the case, it is well to allow a 

 clearance of a few inches around them. This prevents the 

 vibration of the stage disturbing the new work, and allows of 

 the piles being protected from the ravages of sea-worms by 

 grouting them up, later on, with cement grout. If this be not 

 done, voids, which may afterwards give trouble, are likely to be 

 formed in the work. 



Mr. W. Smith, M.I.C.E., engineer to the Aberdeen Harbour 

 Commission, in describing some damage which had been done 

 to the Aberdeen south breakwater, said 



" The piles, where they passed through the superstructure, were 

 found to he eaten away by sea- worms, leaving spaces 2 feet in 

 diameter between the blocks. 



" The destructive influences bearing on the south breakwater 

 since its construction had been : 1st, the scour on the foundations of 

 the seaward face by the seas coming from the north-east, concentrated 

 by deflection along the side of the breakwater ; 2nd, the compression 

 of air in the open joints of the blocks, and in small cavities formed 

 accidentally by disintegration of the surface of the concrete, by the 



