ni = tan a^; 



n = coordinate normal to ground surface; 



n = normal stress acting on rupture plane; 



p = resultant stress acting on plane parallel to ground slope; 



r = resdltant stress acting on vertical plane; 



S = seepage force per unit area, and generalized incremental shear stress; 



s = coordinate parallel to ground surface; 



t = tangential stress acting on rupture plane; 



u, V = parameters in equations for failure surfaces; 



X = horizontal coordinate of point on failure surface measured from intersection 

 of failure surface with ground surface; 



Xq = horizontal coordinate of intersection of failure surface with phreatic 

 surface in (x, y) coordinate system; 



x' = coordinate of point on failure surface measured parallel to ground slope 

 from intersection of failure surface with ground surface; 



y = vertical coordinate of point on failure surface measured from intersection 

 of failure surface with ground surface; 



y' = coordinate of point on failure surface measured vertically below ground 

 surface; 



z = vertical depth below ground surface; 



zi = critical depth when phreatic surface coincides with ground surface; 



Z2 = critical depth when phreatic surface lies between ground surface and 

 critical depth; 



Z3 = critical depth when phreatic surface lies below critical depth; 



z = critical depth; 

 cr ^ 



z^ = vertical depth of phreatic surface below ground surface; 



a = slope of line from origin of planes to point on Mohr stress circle with 

 respect to horizontal; 



a' = angle between tangent to rupture surface and ground surface; 



= angle of line connecting origin of planes with point of tangency of Mohr 

 stress circle with strength envelope; 



3 = angle of obliquity beneath phreatic surface; 



Y, = buoyant unit weight of soil below phreatic surface; 



32 



