STORAGE AND REGULATION OF AVATER. LI. 



or else fissures may occur in the latter ; and as it is here 

 that tension seems to exist, it is evident that any lifting 

 force must increase the shearing strains in the vertical 

 sections near the toe. 



It will be remembered that a diversity of opinion took 

 place as to the necessity or otherwise for cutting a gullet 

 along the foundations of the Cataract dam, which, when 

 filled with a tongue of concrete, would stop any possible 

 percolation, and it may be of interest to point out what 

 has been clone in this respect in the case of two recent 

 American dams. The Boonton dam at Jersey City is 114 

 feet high, with foundations of shale and sandstone, trenched 

 to sound rock, in which was excavated a gullet 8 feet wide 

 and 15 feet deep, afterwards filled with concrete. 



At Wachusset Dam, Boston, there was 30 feet of exca- 

 vation to schist and granite, which was further excavated 

 for the body of the dam to a further depth of 13 feet, below 

 which was cut a trench 20 feet wide and 14 feet deep to 

 receive the concrete tongue. It would seem therefore, 

 that although in the Cataract dam such a cut off trench 

 might possibly be unnecessary, yet in view of the enormous 

 interests involved, not the slightest risk should be taken. 



When concrete is used in the construction of storage 

 dams, it should not be rammed in the ordinary way, with 

 heavy broad faced rammers, as such ramming will only 

 consolidate the top surface to the depth of a few inches. 

 To ensure solid work the mortar should be puddled round 

 each stone by means of blunt spades or other similar tools, 

 so as to leave no cavities. In the construction of the 

 Boonton dam light rammers were used to "joggle" the 

 stones to ensure the concrete flowing into all the cracks 

 and crevices, and at the Bhatgarh Dam it was specified 

 that the concrete was to be carefully worked up with 

 stakes. 



