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Where retaining walls are underlain by weak soils, the overall stability of the soil mass containing the retaining wall should be checked with respect to the most critical surface of sliding. A minimum safety factor of 2.0 is desirable but may not always be achievable. A technique known as slip circle analysis can be used […]

To provide adequate resistance against sliding, the base of the wall should be at least 3 ft below ground surface in front and below the depth of frost action, depth of seasonal volume change, and depth of scour. Sliding stability should be adequate without including passive pressure at the toe. If insufficient sliding resistance is […]

8.4.1 General Criteria Rigid retaining walls are those that develop lateral resistance primarily from their own weight. Figure 8.20 shows the terms used in the design of this type of wall. On the basis of their overall cross-sections, those walls may be referred to as L walls or T walls. (See insets, Fig. 8.3.) Pennsylvania […]

The equation for shearing strength S (lb/ft2 or kPa) of a soil may be taken as follows: S = c + a tan ф (8.3) where c = cohesion, lb/ft2 (kPa) a = confining pressure or normal stress, lb/ft2 (kPa) ф = angle of internal friction of the soil, degrees The shearing strength of the […]

Bedrock is divided by geologists into three large groups, namely (1) igneous, (2) meta — morphic, and (3) sedimentary. Igneous rocks are those that have resulted from the cooling and crystallization of molten masses of mineral matter and gases either at or below the earth’s surface. Sedimentary rocks consist of the transported and subse­quently indurated […]

Retaining wall design engineers not fully trained in soil mechanics need to be acquainted with certain basic principles, in order to understand the data developed by the geotechnical engineer or geologist responsible for the subsurface exploration. Soil is a nonhomogeneous earthen material that varies laterally and vertically in mineral context, grain size, density, grain shape, […]

8.3.1 General Considerations Since the stability and safety of a structure—more specifically, retaining wall structures— depend upon the proper performance of the foundation, it is important that an adequate foundation investigation be made. The purpose of the investigation is to provide the designer with information concerning the engineering properties of the subsurface condi­tions. Generally, a […]

The active pressure coefficient Ka is given by Coulomb theory as where 0 = angle of slope of back wall to horizontal, degrees ф’ = effective angle of internal friction, degrees 8 = angle of wall friction, degrees P = angle of back slope, degrees Refer to Figure 8.12 for the force diagram. The resultant […]

For yielding walls, lateral earth pressures can be computed assuming active conditions and wedge theory, using a planar surface of sliding defined by the Rankine theory. Table 8.1 provides soil properties for computing active earth pressures for five types of soil. Table 8.2 provides friction factors and adhesion for dissimilar materials. See Figs. 8.10 and […]

Lateral earth pressure loadings are applied in various states—specifically, active, at-rest, and passive states. The state of pressure to be considered varies with the wall type. Yielding Walls. Yielding walls are free to translate or rotate about their top or base. For such walls, the lateral earth pressure may be computed assuming active conditions and […]