EXAMPLES OF WALL SECTIONS. 



'45 



At flood tide, when the water had risen sufficiently, the barge 

 was placed over the block (Fig. 124), the four T-headed suspend- 

 ing bars were then lowered into the vertical holes in the block, 

 turned at right angles, and the 



. . ,.,, i A ,1 ,! r- 1 H W.O.S.T. 



chains tightened. As the tide rose, 

 the barge was immersed until the 

 displacement equalled the weight of 

 the block, which in sea- water would 

 be about 55 tons, the barge then 

 drawing about 3 feet with the block 

 just clear of the bottom. 



The barge, with the block at- 

 tached, was then towed to the posi- 

 tion the latter was intended to 

 occupy in the work, and, when the FlG 124. 



tide had fallen sufficiently, it was 



carefully lowered into its place. It was found, after a little 

 practice, that the blocks could be laid with great precision in 

 two courses, one over the other (Fig. 124). 



The system adopted at Brest possesses many advantages to 

 recommend it, where the conditions generally are favourable. 

 The submerging of the block not only reduces the weight to 

 be lifted, but its position during transit increases the normal 

 stability of the barge, enabling it to bear with safety the dis- 

 turbing influence of the waves. 



The block being suspended from the centre of the barge 

 instead of from the end, the necessity of a counterpoise weight 

 is obviated and the displacement reduced by one-half, and the 

 dimensions of the barge decreased in proportion. These may 

 be considerations of great moment when the work is to be 

 carried out in a confined or crowded river or harbour. 



An essential condition in all cases where heavy blocks have 

 to be floated into position is fine weather. That method, there- 

 fore, will be the most applicable which, under all the conditions 

 obtaining, admits of every advantage being taken of favourable 

 weather, so as to ensure the manipulation of the greatest number 

 of blocks in the shortest time. 



Fiume. A modification of the same method was adopted in 

 the construction of a deep-water quay wall at Fiume, on the 

 north-east shore of the Adriatic, where the rise of tide is but 

 slightly over 3 feet. 



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