Building Design and Construction Handbook - Merritt - Ventech!

SOIL MECHANICS AND FOUNDATIONS 6.79
FIGURE 6.34b Cantilever and counterfort
retaining walls. (From NAVFAC DM-7.2,
1982.)
times Q. Thus, the resultant force (P 2), in kN per linear m of wall or lb per
linear ft of wall, acting on the retaining wall due to the surcharge (Q) is equal
to P 2 � QHk A, where Q � uniform vertical surcharge acting upon the entire
ground surface behind the retaining wall, k A � active earth pressure coefficient
(Eq. (6.30) or Fig. 6.35), and H � height of the retaining wall. Because this
pressure acting upon the retaining wall is uniform, the resultant force (P 2)is
located at midheight of the retaining wall.
4. Active Wedge: The active wedge is defined as that zone of soil involved in the
development of the active earth pressures upon the wall. This active wedge must
move laterally in order to develop the active earth pressures. It is important that
building footings or other load-carrying members are not supported by the active
wedge, or else they will be subjected to lateral movement. The active wedge is
inclined at an angle of 45� � �/2 from the horizontal.
Passive Earth Pressure. As shown in Fig. 6.34, the passive earth pressure is
developed along the front side of the footing. Passive pressure is developed when
the wall footing moves laterally into the soil and a passive wedge is developed. In