LOCKS. 



145, 



first condition will be unnecessary, since assumptions are identical. An exception 

 to this might occur with movable dams of high lift, as the water outside the chamber 

 presses on the sloping face of the river wall, while on the land wall it would press on a 

 vertical face. 



Let ABCD (Fig. 2) represent the proposed section of the wall, W its total weight 

 per foot run, T the earth-pressure on the back of the wall per foot, which may be 



FIG. 2. 



h 

 assumed as acting normally to it at a height equal to , and P the pressure per foot 



<J 



from the lower pool, supposed to have seeped behind the wall. The other letters are 

 the same as before. 



If w = the weight of the masonry per cubic foot, 



wh. 



W=(a 



6). 



If the wall is on a porous foundation, we have an upward pressure on DC from the 

 lower pool, since it extends under the floor of the lock as well as behind the wall. 

 This pressure per foot run is bH X 62 J = P', and acts at the center of DC. 



The pressure P is 



TT T72 



H X sec a X X 62$ Ibs. = sec a X 62^ Ibs. 



2 2 



The pressure T of the earth, if the earth is assumed as level with the coping, and 

 without friction on the back of the wall, is 



Weight of triangle AGP X GJ 

 ~~ 



