ABSTRACT
Table 11.2b Active earth pressure coefficients KA for B = 0, f3 varies from -30° to + 30° and a. from 70° to 110°
where KA is the active earth pressure coefficient.
K - sin2 (a + ¢)
JA-sin2 a sin(a - 0)[1 + sin(¢ + 8) sin(¢ - f3) (11.51)sin(a - 8) sin(a + (J) The total normal component Pn of the earth pressure on the back of the wall is
1 Pn =Pa cos 0 =2.r H 2KA cos 0 If the wall is vertical and smooth, and if the backfill is horizontal, we have
(J=.8=O and a=90° Substituting these values in Eq. (11.51), we have
1-sin ¢ ( ¢) 1K = =tan2 45°-- =- A 1+ sin¢ 2 Nt/J
(11.52)
(11.53)
(11.54)
The coefficient KA in Eq. (11.53) is the same as Rankine's. The effect of wall friction is frequently neglected where active pressures are concerned. Table 11.2 makes this clear. It is clear from this table that KA decreases with an increase of 8 and the maximum decrease is not more than 10 percent.
