that liquefaction is very likely, the site is hazardous to an extent. In 

 this situation, if the anchor is loaded in any manner during the earth- 

 quake (such as with a subsurface buoy) or within a time of about 0.2 

 t , (Figure 6-5) immediately following the earthquake, the anchor will 

 likely fail. For soils that will liquefy under earthquake loading, the 

 value of t , is typically quite short - a matter of minutes at most. 

 Situations that classify as potentially liquefiable are potentially hazar- 

 dous in the same manner. Factors of safety relative to the anchor load 

 or anchor capacity are meaningless in this type of earthquake loading 

 as the entire soil mass is in a state of failure when liquefaction occurs. 

 For anchors that are loaded for a significant percentage of the time in 

 areas prone to major earthquakes, site conditions which indicate a 

 potential or likelihood for liquefaction should be avoided. For applica- 

 tions having a lower consequence of failure, the possibility (typically a 

 low probability over the lifetime of an embedment anchor system) of a 

 major earthquake in the vicinity and the resultant possiblity of an 

 anchor failure may be acceptable. 



Standard Penetration Resistance (blows/ft) 

 20 40 60 



- y. 



A ■ ■ I 



- 



- y 



/ / /\ Liquefaction \ 

 ///A very unlikely 1 



- 



V 



V///A ( 



Depth 



Lique- ' 

 faction 



'Liquefaction / 

 /potential I 

 /depends on 1 1 

 i,soil type and A 



of 

 Interest 



very 

 likely 



[earthquake / X ' 

 [magnitude /A 



- 







>. 





 



Medium 

 Dense 



Den 



>e 



Very 

 Dense 















Relative Density 



Standard Penetration Resistance (blows/ft) 

 20 40 60 



(a) Maximum ground surface acceleration = .15g 



Depth " 



of 

 Interest 



Liquefaction 

 potential 

 depends on 

 soil type and\ 

 earthquake /\ 

 magnitude// A 



I///7//A 



Very 

 Dense 



Relative Density 



(b) Maximum ground surface acceleration = .25g 



Figure 6-10. Liquefaction potential profiles for earthquake loading of 

 granular soils (from Seed and Idriss, 1971). 



59 



