Curtis — Pressure of Earth against a Retaining Wall. 



11 



line inclined to the horizon at an angle p, greater than ; if, then, 

 supposing the earth about to slide along DC, we regard the weight 



D 



Fig. 2. 



of the wedge, whose mean vertical section is the area AZDC, and 

 whose thickness is one foot, to he supported by the resistance, 

 including friction, of the plane whose trace is CD, and of the wall, 

 the angle of friction between which and earth is denoted b j ; we 

 must have equilibrium between the weight of the prism (a vertical 

 force, W), the resistence of the plane CD (a force, JR, inclined to 

 the perpendicular to CD at the angle (p, or to the vertical at the 

 angle /3 - 0), and the total resistance of the portion of the wall 

 under consideration (a force P, inclined to the horizon at an angle 

 a + <f/); therefore, by the triangle of forces we obtain the equation 



W sin {(5-(jj) 



P cos (a + + ^' - j3) 

 or, putting a + (f> + (p' = y, 



P sin O - (j>) 



or. 



W cos (7 - i3)' 

 log P = log W + log sin (jS - ^) - log cos {y - ft)- 



