108 CONSTRUCTION 



moulded before driving and those that are moulded after- 

 ward. Those of the first class must be reinforced. The 

 Chenoweth and the Cummings and the Hennebique are 

 pre-moulded piles, and there are also many unpatented 

 types of the same class. Those of the second class are of 

 various forms, as the Simplex, the Raymond and the 

 Pedestal. 



Concrete piles are much to be preferred when acting 

 as columns, resting on a hard substratum. They are more 

 durable than wooden piles in ground which will subsequently 

 be dried out through the absorptive action of adjacent 

 brick sewers and are thus especially suited for use in cer- 

 tain park lands. They are used to support arch abutments 

 and masonry retaining walls. 



MASONRY WALLS AND STEPS 



Retaining Walls. One of the most important of the 

 practical matters to be attended to is the excavation for 

 the foundation. It is not necessary that the foundation 

 should extend down to the bottom of frost. The heaving 

 effect of frost can be entirely eliminated by digging down 

 2| feet below the finished grade. 



The foundation pit should be excavated true with ample 

 room on the front side for the construction of a good square 

 toe. Skimping on the front side of the foundation has 

 resulted in the failure of many retaining walls. 



Walls for shore protection should be founded on good 

 soil. The use of spud piles is not in general to be recom- 

 mended. It is better to excavate to a hard foundation. 

 The reason for this lies in the fact that excavation in front 

 of a shore wall or sea wall permits fine sands, " liver " 

 and quick-sands to flow away from under the foundation, 

 thus endangering its stability. 



