262 



HARBOUR CONSTRUCTION. 



Should the site be such as to admit of mass-concrete within 

 frames being used, this mode of construction may be resorted 

 to after the slopes have been benched assuming such to be 

 necessary and the more awkward holes and other inequalities 

 roughly levelled up ; but should the site be too exposed for this 

 class of work, a level bed, upon which to found block-work, may 

 be obtained either by means of bag- work (pp. 188 et seq.), or by 

 mass-concrete deposited and levelled off in the manner which 

 will be presently described (pp. 266 et seq.) 



2. Steeply inclined surfaces on the site of the breakwater, 

 running either parallel to it or crossing it obliquely, as indicated 

 in Fig. 81. 



CROSS SECTION OF BREAKWATER, 



FIG. 81. 



The only satisfactory way of dealing with such cases is to 

 bench the rock, either as represented in the above sketch, or by 

 a series of stepped benchings, as circumstances may determine. 

 This will be facilitated by the use of light charges of dynamite 

 or other suitable explosive. Heavy charges, although effecting 

 a saving in time and labour, are likety to do mischief by shaking 

 and breaking up the rock upon which it is intended to found 

 the work. 



3. Steeply inclined strata, intersected by gullies, which are 

 often partially filled by boulders, gravel, and sand. 



The danger to be guarded against here is the slipping of the 

 rock strata * upon each other when loaded with the breakwater. 

 This may be prevented either by filling the gully with 

 concrete (after the removal of the boulders, gravel, etc., from it), 

 by which means the ends of the strata will be supported, and 



1 The joints or beds of cleavage, in granite and other igneous rocks, are often 

 equally dangerous. 



