Table 13 cont'd 



Notes Angles of friction should be reduced by about 5 degrees if 

 the wall fill ^idll support train or truck traffic. The coefficient 

 of friction f wou].d equal the tangent of the new angle 01 , 



23^<^ Earth pressure agaj-nst structures or ii^regular section such 

 as stepped stone blocks or those having two or more back batters may 

 be conputed by equation ^2 by substituting an approximate average 

 back batter to determine the angle (©)= 



236 » Application of the Resultant of Earth Force s - For all 

 structures T»jith hydrostatic pressure or negative sloped baclcfills, the 

 resultant of force should be considered to act at 0*33 of the height* 

 For structujres having batters on the back face equal to or greater 

 than 2 on 1, the earth pressure should also be applied at 0,33 h» 

 For structures mth vertical back faces (or batters less than 2 on l) 

 and horizontal or positive sloped backfills the earth pressures 

 should be applied at Oj.375 h* (See Figures 83 and 8ii). 



237s Earth Pressures - Passive Forces ,, - Though the passive 

 resistance of an earth mass to movement is very much greater than the 

 active pressure, to develop this passive resistance to movement, the 

 wall must translate or rotate to a significant degree* Therefore, ex- 

 cept for sheet pile structures, the passive resistance should not be 

 considered in a stability analysis «. For sheet pile structures the 

 passive earth resistance may be coitputed as 



Rp = wh^ tan^ l/2 (90 + 0) (53) 



238* Surcharg e Loads ^ " For a uniform, surcharge the density of 

 backfill material may be assumed to be increased in the follotidng 

 m.anner j 



Let ¥ = the surchax'ge load in pounds per square foot 



x^r ~ the unit weight of backfill material, either drained 



or saturated dependent on baclcfill condition 

 h = the vertical height of fill in feet 



h' -^ 

 w 



then x^-» the nex<r value of unit baclcfill weight is given by 



(h + 2h') f^),s 



w' = w -^— ™r C54j 



>Jhen this procedure for dealing with surcharge loads is adopted, the 

 point of application of the active thrust for vertical walls iri-th 

 horizontal or positive sloped baclcfill should be raised from 0.375^ li> 

 at the rate of 0.01 h for each 10 percent increase in the artificial 

 density, to a limit of OMl^ h. 



121 



