THE IRRIGATION AGE. 



899 



It is, of course, conceivable that the distribution of the 

 material might be so at variance with the changes of pressure 

 in depth, that the above calculations, with regard to the fac- 

 tor of safety of the arch, would not hold. This matter, how- 

 ever, has been closely considered and each horizontal cross- 

 section has been designed with regard to the shearing strain 

 which is closely related to the strains above considered. 



Second The proportioning of the face wall. 



In this case it is assumed that the water comes flush 

 with the top of the dam. The parapet or extra height of any 

 dam varies with the nature of the case and in this recitation it 

 is omitted. The theoretical width of the face wall at the top 

 is zero. It is, however, designed to be 2 feet thick to resist 

 nave action. The entire width on top, counting earth filling 

 and enclosing walls, will be 23' 4^"- As the pressure against 

 this wall varies as the depth, and as the top is unnecessarily 



thick, the bottom is the place to test the factor of safety. In 

 so doing, we will neglect the strengthening effect of the bed- 

 rock key. 



The face wall is divided into vertical panels by the but- 

 tresses, the one in the center measuring 20 feet horizontally 

 and 185 feet vertically. These panels may be considered as 

 consisting of horizontal slabs or simple beams being sup- 

 ported at each end and being subjected to a uniform load 

 between supports. When the reservoir is full, there will be a 

 pressure on the outside of each slab equal to the weight of the 

 water over the slab considered. When the reservoir is empty, 

 the weight of the earth filling may press outwardly against 

 the slab. The water pressure is easily figured and the maxi- 

 mum possible pressure of the earth filling can be readily 

 ascertained, but there are other possible strains not so easily 

 estimated. There is an indeterminable strain due to a possible 



BANCROFT Df\n 



PATENTED. 



