COLUMNS AND STRUCTURES 



2S9 



x being the angle of surcharge. The length of the line AE is 

 fixed l>y the intersection of the angle of repose drawn from the 

 bottom of the wall and the angle of surcharge drawn from the 

 top of the wall. From tlu> middle point of the line AE a semicircle 

 ABDE is drawn. 



The angle C is the angle of friction of the filling against the 

 back of the wall. The line IH is drawn at an angle with the 

 back of the wall equal to the sum of the angle of repose and 

 the angle of friction C to an intersection with the line AE. 



From .A as a center, with a radius = A B, describe an arc cut- 

 ting A E at F. Draw FJ parallel with the line IH. With radius 



Fig. 183 Graphical Method for obtaining Pressure against Retaining Wall 



FJ describe an arc intersecting the line AE at G and draw the 

 triangle FJG. 



The line AJ is the cleavage line of the material and the area 

 of the triangle FJG multiplied by the weight of a cubic foot of 

 the material will give the pressure against a strip of the wall 

 one foot long. This pressure is considered to be concentrated at 

 a point above the base of the wall equal to one-third the height, 

 the height being measured from the bottom of the wall, and not 

 from the surface of the ground. The direction of this thrust T 

 is not determined, authorities not agreeing. Some assert that 

 it is parallel with the slope of the surcharge and some that it 

 makes an angle, C, with the back, while others count it as a hori- 

 zontal thrust. H n the figure it is drawn parallel with the angle 

 of friction. A larger moment is obtained by considering the 

 thrust as horizontal and a wall designed to resist this horizontal 



