82 DAMS AND HEADWORKS 



7. Allow for wave action. 



8. Where necessary, reinforce the dam with steel. 



On account of their great weight, gravity dams should neces- 

 sarily be placed on bedrock foundations, and the materials should 

 be carefully tested as to their bearing power. The fact should 

 also be kept in mind that the pressure is not uniform over the 

 entire base but varies according to the water level back of the dam. 

 For example, with the reservoir full, the pressure is, of course, a 

 maximum at the toe and decreases toward the other side. All 



FIG. 36. Typical Masonry Dam of the Gravity Type. Appalachian Power 



Company. 



tendency of seepage should be prevented by sealing all fissures, 

 and drains should be provided for carrying any waters that may 

 reach the base or enter the structure. 



The material of which gravity dams are built consists either 

 of concrete or rubble masonry. With the former the rocks are 

 crushed to a uniform size making an even mixture, while with the 

 rubble masonry, or cyclopean concrete construction, as it is also 

 termed, large stones, weighing up to ten tons, are used. These 

 are carefully placed in position and the spaces between them 



