i8 4 



HARBOUR CONSTRUCTION. 



in situ, so that all the advantages which such masses afford, in 

 stability and otherwise, are secured without its being necessary 

 to provide costly plant for dealing with such loads. Indeed, 

 monolithic blocks are often made of such weight that no lifting 

 appliances, in reason, could cope with them. 



The system is not, however, without serious drawbacks. It 

 is essentially a fine-weather method of constructing work, and 

 those who adopt it must be prepared for interruptions and 

 losses, arising alike from injury to the frames and to the soft 

 concrete deposited within them, the frames being specially liable 

 to derangement before the concrete is put into them. 



PARAPET 

 (if required) 



Concrete Capping. (Mass-work.) 



Concrete Blocks. 



Mass Concrete, 

 deposited within temporary frames. 



HIGH WATER 



LOW WATER 



FIG. 32. Type section of breakwater formed of concrete blocks on base of mass-work. 



When depositing concrete under water, very great care is 

 necessary to prevent loss of cement. 



The method usually adopted in constructing this class of 

 work is to erect a framing of wood or iron, consisting of up- 

 rights, the ends of which rest either in shoes, or, if the sea-bed 

 is of rock, in holes drilled therein, to which horizontal bars or 

 wales are attached. To these are fixed planks, usually from 

 3 to 4 inches thick, which form the sides of the frame. The 

 lower ends of these rest upon the sea-bed, or other base, and 

 conform to any irregularities which may exist. 



In cases where the foundation is very irregular, it may be 

 necessary to cut the bottoms of the planks to fit it ; but, should 



