i8o 



HARBOUR CONSTRUCTION. 



the bottom course of blocks requires to be done with very great 

 care. This having been satisfactorily accomplished, the blocks 

 are lowered by the setting-machine, and placed in position by 

 the aid of divers. Those below low water are of necessity laid 

 " dry " that is to say, without cement or other adjusting medium 

 between them, such as a bed of mortar would afford and this, 

 unfortunately, constitutes a serious defect, seeing that, unless the 

 surfaces are perfectly true, and the blocks laid in precisely the 

 same plane (which can never be the case in practice), they bear 



PARAPET 

 (if required) 



Concrete Capping. (Mass Work.) 



1 i r 



Concrete Blockivork. 



i , i , L 



HIGH WATER 



LOW WATER 



ALTERNATIVE MODE OF FORMING 

 FOUNDATION WITH MASS-CONCRETE. 



(see page 266. ) 



FIG. 30. Type section of breakwater formed of concrete blocks laid 

 in horizontal courses. 



upon each other on points and edges only, which is apt to cause 

 breakage of the blocks and dislocation of the work (see p. 244). 



The difficulty is increased if unequal settlement should take 

 place, or if several courses have to be laid, in this manner, one 

 upon the other ; indeed, sometimes the unevenness is such that 

 the block surfaces have to be pick-dressed and levelled by mason- 

 divers as the work proceeds, an operation which entails much 

 expense and loss of time. 



