earth pressures (fig 14-8). Generally, a linear variation

in earth pressure coefficients with depth may be

a. Criteria forselecting earth pressures.

assumed between the sections of wall.

(1) The equivalent fluid method should be

(4) Consider passive pressures in the

used for estimating active earth pressures on retaining

design if applied loads force the structure to move

structures up to 20 feet high, with the addition to earth

against the soil. Passive pressures in front of retaining

pressures resulting from backfill compaction (fig 14-8).

walls are partially effective in resisting horizontal sliding.

(2) For walls higher than 20 feet, charts,

b. Overturning. Calculate the factor of safety,

equations, or graphical solutions should be used for

FS, against overturning, defined as the ratio of resisting

computing lateral earth pressures, with the addition of

moments to the overturning moments. Calculate the

earth pressures resulting from backfill compaction.

resultant force using load diagrams shown in figure 14-1,

(3) Use at-rest pressures for rigid retaining

as well as other loadings that may be applicable. Use

structures resting on rock or batter piles.

Design

only half of the ultimate passive resistance in calculating

cantilever walls founded on rock or restrained from

the safety factor. The resultant of all forces acting on the

lateral movement for at-rest pressures near the base of

retaining wall should fall within the middle third to provide

the wall, active pressures along the upper portions of the

a safety factor with respect to overturning equal to or

wall, and compaction-induced earth pressures from the

greater than 1.5.

top to the depth at which they no longer increase lateral

(Courtesy of R. B. Peck, W. E. Hanson, and T. H.

Thornburn, Foundation Engineering, 1974, p 309. Reprinted

by permission of John Wiley & Sons. Inc., New York.)14-5

Figure 14-4. Active and passive earth pressure coefficients according to Coulomb theory.

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