Figure 26. — View from below site 

 917H-3, illustrating its long, 

 narrow, and shallow characteristics. 



Plan view and profile sketches of the site are presented in figure 28. The seismic 

 interpretation at traverse 1 is: 6.7 feet of loose material (1,140 f.p.s.) overlying at 

 least 35 feet of solid rock (10,000 f.p.s.). 



Although the road cut intersected the bottom of the swale, it is difficult to state 

 with certainty that this resulted in sufficient loss of support to cause failure. By 

 using appropriate techniques for the analysis of stability of a cohesive, infinite slope, 

 it is apparent that the natural slope might have failed in the absence of road construc- 

 tion. Such an analysis follows: 



Assume a natural slope, i = 70 percent (35°), void ratio, e = 0.86 (y^ = 89 p.c.f.), 



and average depth to failure surface, H = 5 feet. The appropriate relationship for the 

 dry condition is : 



- cos^i (tan i - tan <|>). 



Since i = <j>, no cohesion is required for stability in the dry condition. 



