STORAGE AND REGULATION OF WATER. XLIX. 



a. There is the tension at the tail of dams, but it is not 

 of first class importance, because 



b. The tension in the substructure is much greater than 

 in the tail, and the substructure, not the dam, is the weakest 

 part. 



c. Rupture will take along a line drawn from the tail at 

 an angle of 45° towards the toe. 



d. The shear in the base is neither triangular nor para- 

 bolic, but is maximum towards the front of the dam, mini- 

 mum towards the centre, with a second maximum towards 

 the toe. 



As I understand it, the shearing alluded to may some- 

 times be rather a crushing by shearing, as when a short 

 stone column fails by sliding taking place along a single 

 plane surface or an angle of about 45° with its sides. 



As regards the vertical shearing strains it would seem 

 that the critical section is through the point where the 

 resultant cuts the base, as it is at this point that the dam 

 would tend to overturn, supposing the support of the toe 

 was removed. That is to say, the support afforded by the 

 toe might equally well be afforded by means of a chain 

 attached to the base of the dam at this point and fastened 

 to a point vertically above it. If the face of the dam were 

 lifted it would overturn either by the breaking of this 

 chain, that is by the masonry shearing or by turning over 

 on the toe. 



Some very interesting experiments on a dam profile con- 

 structed of thick indiarubber, have been carried out by 

 Messrs. Wilson and Gore, which generally prove the state- 

 ments made by Messrs. Atcherley and Pearson. The 

 rubber was ruled into squares, each of which was strained 

 by means of weights of the correct calculated amounts 

 representing the water pressure, the weights of the dam 



4-June28, 1905. 



