Figure 25. — Safety factors vs. 

 arc radius, R 3 for site 917-3 , 

 with zero boundary neutral 16 

 stresses. 



1.5 - 



1.3 - 



O 



2 1.2 Y 



1.1 - 



1.0 



20 60 100 140 180 220 260 



ARC RADIUS, R (Feet) 



and 38°, respectively. Under the extreme condition that would permit seepage through- 

 out the fill, with a top flow line coincident with the fill slope, the necessary 

 developed cohesion values would be 0.83 and 0.75 p.s.i. for $ - 35° and 38°, respec- 

 tively. Such an extreme seepage condition seems unlikely at this site, although it has 

 already been noted that water collected on the road at this location. It is possible, 

 however, that water infiltrating from the road surface combined with the ground water, 

 resulting in emergence of the water at some location above and near the toe of the fill 

 slope. A subsequent "blow out," or quick condition might have occurred locally, and 

 the resultant loss of support at the toe would have allowed the upslope material to 

 slide. 



In any case, the analyses of this site and of site 917-1 seem to indicate that a 

 more realistic value for the friction angle in this material might be about 38°. 



One additional factor should be noted in connection with site 917-3. Timber has 

 been left standing at and below the toe of the fill slope. It is believed that these 

 live trees and their fully developed root systems significantly enhance the stability 

 of the site. Most certainly they were instrumental in preventing complete translation 

 downslope of the material which partially failed. 



Site 917H-3. This site is a relatively long, narrow failure of material lying in 

 a swale above Road 917H at a location within 100 yards of site 917H-2. It is pictured 

 in figures 26 and 27, as viewed from the bottom and top of the failure, respectively. 



2" 



