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10-18 CNIL ENGINEERING REFERENCE MANUAL 26 HORIZONTAL PRESSURES FROM (ems. These forces result from the distributions shown SATURATED SAND in figtlre 10.20. They aze the forward (active or ten- sioned) earth reaction, RA, the backwazd (passive or 1 Sand, being porous, allows trapped water to exert a hot- compressed) earth reaction, RP, the soil force, Rv, the izontal pressure against vertical retaining walls. There- shear resistance, R„ the weights of the earth masses, fore, the sand and water both exert a horizontal torte. RT and Ry, and the weight of the wall itself. The hydrostatic pressure is Phydrostatic = (62.4)H 10.13 0 However. there is also a buoyant force. since each sand particle is submerged below the water table. The soil °, H pressure depends on its saturated density and the buoy- trust ant force. penetration '~a. Bl 'o' heel B~ Peo~l, vertical = (Psat - 62.4)H 10.74 h . ~~ a horizontal = kA (Plat -62.4)H 10.7$ Psoil . , toe . optional key B The total horizontal pressure from saturated soil is the . sum of equations 10.73 and 10.75. Figure 10.19 A Cantilever Retaining Wall Phorizovtal = I62'4 + kA (Psat - 63.4)JH 16.76 . The increase in the horizontal pressure over the dry condition is (1 - kA)(62.4). This product is known as . the effective hydrostatic loading of the fluid. IC it is con- . venient to do so, equation 10. i 6 can be interpreted as a pressure from a fluid with egecttve hydrostatic density • PeR~~O • Peti = 62.4(1 - kq) 10.77 Phorizontal = IkAPsat + PeR~H 10.i8 The saturated soil density used in the above equations • can be calculated i( the dry soil density and either the porosity or void ratio is known. Figure 10.20 Pressure Distributions • e Psat = Pary t 62.4n = Pary t 62.4 ) 10.79 on a Retainin Wall g 1 t e 27 RETAINING WALLS The important factors to be considered when evaluating • the design of a retaining wall aze factor of safety against • Retaining walls must be sate against settlement. In this overturning, the maximum soil pressure under the base, regard, their design is similar to footings. They must and the (actor of safety against sliding. • have sufficient resistance against overturning and slid- ing. Retaining walls must also possess adequate strut- The following procedure can be used to analyze a re- t inin wall rural strength. The method of meeting these require- g . a • menu is one of trial and error. step 1: Determine the active reaction and its point The analysis of a retaining wall's stability requires of application. Include the reactions from all point, line, and distributed surcharges.~t • knowledge of at ]east six different distributed force sys- • Z0 45 Ibm/ft3 is typically taken as the effective hydrostatic den- 11 Retaining walls should be analyzed and designed for amini- sity of the fluid behind a retaining wall. mum density of SO Ibm/ft3 0( fill, regardle9s of the actual load. • • PROFESSIONAL PUBLICATIONS INC. ~ P.O. Box 199, San Carlos, CA 94070 •