VARIOUS TYPES OF BREAKWATERS. 179 



Obviously, the roadway of such a breakwater as this should 

 be made exceptionally strong, because during a storm it may 

 be regarded as the key to the whole position. 



On the other hand, if it be made air-tight, and the joints on 

 the seaward face of the breakwater be left open, as they too 

 often are, it may be blown up by the stroke of the waves upon the 

 face of the work ; or it may even conduce to the injury of other 

 portions of the work, by preventing the free escape of pent-up 

 air and water. 



There can be little doubt that loose rubble hearting is a thing 

 to be avoided, excepting under very favourable conditions. 



Advantages of using Large Concrete Blocks in Breakwater 

 Construction. 



The employment of large blocks of concrete in constructing 

 breakwaters possesses many advantages over the old system of 

 building with rubble or blocked stone in place. Each in- 

 dividual block is, by virtue of its weight, far better able to 

 resist heavy seas than newly built masonry composed of smaller 

 materials ; and, seeing that the setting of a large block occu- 

 pies very little more time than is required for the setting of a 

 smaller one, the work can be rapidly brought up when once 

 the bottom course has been properly laid, it being thus possible 

 to utilize fine weather to the fullest extent. 



The making of blocks may also be proceeded with concur- 

 rently with the building of the breakwater, as well as during 

 rough weather, when building in the sea is impossible. The 

 workmen, when not engaged on the breakwater, may thus be 

 profitably employed in the workyard, making blocks ready for 

 setting when the weather will permit. 



In building blocks in the block-yard, unharassed by tides 

 and waves, the work can be done in a more perfect and solid 

 manner than is possible in a tideway ; and, seeing that they are, 

 or should be, allowed ample time to harden before being put into 

 the sea, the risks inseparable from newly built work in the sea 

 are much reduced. 



3. Breakwaters formed of Concrete Blocks laid in Horizontal 



Courses. 



In this class of breakwater illustrated in Fig. 30 the pre- 

 paration, and especially the levelling, of the foundation to receive 



