VARIOUS TYPES OF BREAKWATERS. 181 



At the low-water course bedding the blocks in cement is 

 commonly commenced ; and it is here where delay so often takes 

 place, while waiting for the coincidence of spring tides and fine 

 weather to enable the work to be proceeded with. 



This trouble is the same whether the base for the low- water 

 course is of blocks or of mass-concrete, and it is largely owing to 

 the difficulties which are experienced at this stage of the work 

 that the construction of breakwaters of this and similar types 

 in exposed situations often proves so tedious and costly. 



When the upper courses have been satisfactorily set in 

 cement and grouted, they are practically monolithic. 



The blocks of the top course may with advantage be moulded 

 with sinkages, similar to the " frogs " in bricks. This gives the 

 capping an additional hold, and also ties the blocks together. 



The capping is commonly formed of mass-concrete deposited 

 in place ; and, with the view of preventing unsightly cracks, it 

 should be moulded in short lengths, each length covering not 

 more than two, or at the most three, rows of blocks. 



A breakwater constructed in the manner just described should 

 have an unexceptionable foundation, otherwise unequal settle- 

 ment is almost sure to occur, resulting in manifold evils. The 

 "Titan," or setting-machine (assuming such to be used), as it 

 advances upon each succeeding length of the new work, is often 

 responsible for a good deal of trouble in this respect. 1 Further- 

 more, should local settlement take place, the dry-set blocks are 

 liable to fall away from the top monolithic work, and when thus 

 relieved of weight they are easily drawn out by the waves, thus 

 causing serious damage to the work as experience has often 

 shown (see Fig. 31, p. 182). 



In these respects, as in others, the sloping-block system, 

 which will be shortly described, possesses many advantages, one 

 point especially in its favour being that during construction the 

 work is to a great extent independent of the tides. 



All bags of concrete used in levelling up foundations should, 

 where practicable, be laid athwart the breakwater, and the 

 interstices should be filled and carefully levelled by means of 

 smaller bags containing specially soft, rich concrete, or with 

 similar concrete deposited in mass (see pp. 266 et seq.). 



1 The "Titan" at Colombo, which in working order weighed 180 tons, caused 

 a settlement of from 3 to 5 inches in passing over new work (Min. Proc. List. C.K, 

 Yol. Ixxxvii. p. 82). 



