t A ft 



seldom exceeds 30 ; in stronger earth it becomes 37 ; and in some fa * 

 rourable cases more than 45. 



1. If h r= A D, x = A E, 6 = D A G, and S and s represent the speci- 

 fic gravities of the wall and earth, the state of equilibrium is expressed 

 by this equation, 



| A-2. S - l / 6 7*2. g. tan, 8 I 8, 



PX. Suppose the wall to be 30.37 feet high, of brick, specific gravity 

 8000, and the bank of earth specific gravity 1428, and the natural slope 

 63; then 



#*. 2000 % X 39.S7 2 X 1428 X tan.s 2GJV 



.". x 9.6 feet thickness of wall.. 



The following practical results may be found useful. 



Values ofD G for different materials.- 



Bank of vegetable earth ~~~*~~***~~*~.~~~ D G =z .618 h, 



Do. of sand ~~~~~~ ~,*~~^~~~^~ D G = .677 h. 



Do. of vegetable earth mixed wHh small gravel *~~ D G =. .646 h. 



Do. of rubbles ~~~~ r ~~~^**~~~*~~~ ^ r ^^^ rff ^. DG = '4J4 h. 



Do. of vegetable earth mixed with large gravel ~~~ D G .613 h,. 



Thickness of walls, both faces vertical 



1. "Wall brick, 109 Ibs. per cubic foot, bank vegetable 1 



earth carefully laid course by course ^- , D F = .16 : ^. 



2. Wall unhewn stones, 135 Ibs. per cubic foot, earth 



as before ^-^ ,~~*^+~~*~~ ^^ DF .15-&. 



3. Wall brick, earth clay well rammed ~~~~ , DF .17 h. 



4. Wall unhewn stones, earth as before ^^r^^.^^^ 13 F .16 h, 



5. Wall of hewn freestone, 170 Ibs. per cubic foot, 



bank vegetable earth ^^^^^^^^^^^^^^ D F .13 K. 



6. Do. bank clay ^^^ fff ^, w ~ ww ~ ww ,. w ~. D F -= .14 h. 



7. Bank of earth mixed with large gravel, wall of 



bricks ~~^ . D F .19' 7>. 



Do. of unhewn stone ,v~*~^,^.~^v~~^,~~~~~ D F = .17 h. 



Do. of hewn freestone *,,..*,..***** D F = .16 h. 



8. Bank of sand. 



Wall of bricks . ~~**~~*~*~. D F - .33 h. 



Do. of unhewn stones .., Mn ,. flf ^ f ~~~ f ~**~~*+ D F .30 A. 



Do. of hewn freestone *,....,., w ,.,.. D F .26 h. 



When the earth of the bank is liable to be much saturated with water* 

 %B proportional thicknesses of the walls must at least be doubled, 

 9i F 



