CURVED CONCRETE WALLS FOR STORAGE RESERVOIRS. LI. 



the purpose well ; and a similar arrangement is about to be carried 

 out in a dam across the Cataract River for the Wollongong 

 Water Supply. 



Theoretically it would seem of little importance how the thicken- 

 ing of the dam was arranged ; whether both sides should have a 

 batter, thus keeping the centre of gravity of all sections in a 

 vertical line in the centre of the dam, or whether the batter should 

 be on the inner or water face, thus obtaining some help from the 

 downward thrust of water on the batter which some engineers 

 have contended to be of service, or to keep the inner or water face 

 vertical and outer side battered. As a matter of fact we have 

 examples of each form in the State. The Parkes Dam having a 

 double batter, and the Tamworth Dam being battered on the inner 

 face, but the standard practice now adopted, and one found in 

 many respects most convenient in construction, is to keep the 

 inner face vertical and the outer face battered. This arrangement 

 suits the outlet works more conveniently, as the swivel offtake 

 pipe can be brought close up to the face of the dam for cleaning 

 without falling back too much. 



Principles upon which the carved dams have been designed. — A 

 curved dam with solid rock abutments being subject to the same 

 stresses as a hollow empty vertical cylinder of the same radius, 

 and surrounded on the outside by water of the same depth as that 

 impounded by the dam, the formula for resistance of cylinders to 

 a crushing pressure, viz. : P = -^~ or ~ has been used for calcu- 

 lating the thickness of the seven curved concrete dams or weirs 

 constructed in connection with the Country Towns Water Works 

 to date with radii varying from 100 feet to, 300 feet. 



The value of s (safe crushing strength of material per square 

 foot) for a dam with granite or basalt abutments, the same stone 

 being used for the concrete, has been taken at 20 tons, and for 

 dams having sandstone abutments, as at Lithgow and Picton, at 

 10 tons to 12 tons per square foot according to local conditions. 



T= Thickness at any point in feet. 



