FOUNDATIONS. 259 



CONCRETE FOUNDATION. 

 System B. 



\Vrought-iron pins or bars, provided with eyes for the 

 reception of bolts or coach screws, are let into the rock at 

 intervals of about 5 or 6 feet, as shown in Fig. 80, and to 

 these are attached temporary planks, roughly cut to fit the 

 inequalities of the rock surface. The upper edges of these 

 planks are set to the required level, and the concrete is then 

 deposited between them. Should the planking be more than 



FIG. 80. 



from 15 to 18 inches in height, stays will be required to enable 

 it to withstand the thrust of the soft concrete, and the action of 

 the waves. Cement-bags filled with sand, laid against the 

 boarding, will often be found to give the amount of support 

 required. 



In order to prevent undermining, any spaces which may 

 exist between the bottom of the planks and the rock surface 

 should be stopped with Medina or Roman cement. If this be 

 not done, jute canvas should be nailed along the lower edge of 

 the planks, on the inner side, and it should have sufficient width 

 to underlie the concrete for a distance of 12 or 15 inches. Should 

 several tiers of planks be used, the joints must be made water- 

 tight, or they must be covered with canvas so as to protect the 

 concrete until it has set. 



The surface of the concrete should be finished off in the 

 manner described for system A. 



Instead of a topping of flat stones, pointed with Medina or 

 other quick-setting cement, the surface of the concrete is some- 

 times covered with jute sacking, weighted down by pieces of 

 iron rails, or in some other way. 



When the weather happens to be favourable, and the chafing 

 action of the waves is not great, this system answers well ; but 

 should the rails be displaced as is too often the case and the 

 sacking become loose, the chafing to which the newly deposited 



