184 



MIDDLEBROOKS. EARTH DAMS 



[Ch. 10 



suit costly changes during construction are not unusual for this type 

 of structure. 



Chute spillways on earth as illustrated by Fig. 4 have been em- 

 ployed in a number of cases where rock was inaccessible at reasonable 



EI.550 



1"0 anchor bars 

 9'c.c. 



Fig. 3. Side-channel spillway, Surry Mt. Dam. Foundation is massive granite 

 gneiss. Infrequent operation. 



Longitudinal drain 

 Transverse drain 



Low water 

 El. 203 



2' gravel drain' 



Fig. 4. Chute spillway, Sardis Dam. Foundation is soil and soft rock. Frequent 



operation. 



depths. Foundation investigations for this type of spillway should 

 be more extensive than for any other type. A cutoff along the center 

 line of the weir section and an elaborate drainage system under the 

 chute and stilling-basin portions are required. The shearing strength, 

 compressibility, and expansion characteristics of the soil are im- 

 portant factors in design. Upheaval of concrete spillway slabs lo- 



