Figure 6. — Stress 

 re lationships 

 for plane A-A ' 

 above the water 

 tab le . 



B 



There are three different conditions for which the obliquity angle can be defined: 



Case I. Plane A-A ' above the water table. When plane A-A' is above the water 

 table the angle of obliquity is equal to the slope angle, 9, as shown in figure 6. 



Case II. Plane A-A' below the water table with the water table coinciding with 

 the ground surface. The obliquity angle, B, is defined in terms of effective stresses 

 as shown in figure 7. The tangent of the obliquity angle is found by dividing the 

 tangential stress by the effective normal stress: 



tan 



Y )sin6cos0 

 sat w 



YrfZ-Z )cos 2 9 

 b w 



(9) 



Solving equation 9 for the angle of obliquity, 3, yields 



tan" 1 [(1+— )tanO] 



(10) 



Figure 7 .--Stress rela- 

 tionships for plane 

 A-A ' below the water 

 table with the water 

 table coinciding with 

 the ground surface. 



RESULTANT 



7 



