Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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Soldier Rev B
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- Figure 9-2: Geometry for active earth pressure.
- Table 9-1: Friction Angle for Dissimilar Materials. Interface Materials
| Figure 9-1: Soldier pile wall. 9.2 EARTH PRESSURES Prior to a performing a p-y analysis for the discrete supporting elements, active earth pressures imposed above the base level of the fascia lagging or panels must be resolved into a resultant force, inclusive of any surcharge loads acting above the wall. AASHTO Section 3.11 describes the un-factored resultant active earth pressure (Pa) for design of permanent non-gravity cantilevered walls as follows Pa = πΎπΎππ πΎπΎβ² ππ π»π» 2 Equation 9-1) acting at H above the design base grade, defined by the bottom level of the panel or lagging below the finish grade in front of the wall, where H = Total wall height measured from the panel or lagging base level Ξ³β = Effective unit weight of the soil retained by the wall l = Contributory length of wall relative to each vertical element (center-to-center spacing) The active earth pressure coefficient (Ka) in Equation 9-1 is derived from Coulomb earth pressure theory, including wall friction as follows sin + sin sin β Equation 9-2) 128 In which ππ = οΏ½1 + sin+ πΏπΏοΏ½ sin+ sin β πΏπΏ) sin + π½π½) Equation 9-3) Where Ξ΄ = Friction angle between backfill and wall. Ξ² = Angle of backfill with respect to horizontal. ΞΈ = Angle of back face of wall to horizontal (normally 90Β°). f Effective angle of internal friction of the retained soil. The geometric variables of Equation 9-3 are illustrated by Figure 9-2. Figure 9-2: Geometry for active earth pressure. Suggested values for friction angles provided in AASHTO Table 3.11.5.3-1 from the US. Department of the Navy (Design Manual 7.02, 1986) for various wall interface materials are listed in Table 9-1. 129 Table 9-1: Friction Angle for Dissimilar Materials. Interface Materials Mass concrete against the following materials Clean sound rock 0.70 Clean gravel, gravel-sand mixtures, coarse sand to 31 0.55 to 0.60 Clean fine to medium sand, silty medium to coarse sand, silty or clayey gravel to 29 0.45 to 0.55 Clean fine sand, silty or clayey fine to medium sand to 24 0.34 to 0.45 Fine sandy silt, nonplastic silt to 19 0.31 to 0.34 Very stiff and hard residual or preconsolidated clay to 26 0.40 to 0.49 Medium stiff and stiff clay and silty clay to 19 0.31 to 0.34 Steel piles against the following soils Clean gravel, gravel sand mixtures, well-graded rock fill with spalls 22 0.40 Clean sand, silty sand-gravel mixture, single size hard rock fill 0.31 Silty Sand, gravel or sand mixed with silt or clay 0.25 Fine sandy silt, nonplastic silt 0.19 Formed or precast concrete against the following soils Clean gravel, gravel-sand mixture, well-graded rock fill with spalls 22 to 26 0.40 to 0.49 Clean sand, silty sand-gravel mixture, single-size hard rock fill to 22 0.31 to 0.40 Silty sand, gravel or sand mixed with silt or clay 0.31 Fine sandy silt, nonplastic silt .25 The values cited above are intended for mass concrete, steel, or precast concrete placed against the various materials listed. Some ground movement beyond that which is required to develop active earth pressure maybe required to realize the full benefit of wall friction ground movement will be influenced by the construction techniques used to install the lagging or panels between the vertical support elements. Long-term earth pressures from stiff clays and plastic silts acting on permanent structures will generally be controlled by the effective stress strength properties. For temporary wall applications in cohesive soils, the active pressure can be determined based on total stress methods and undrained shear strength parameters however, the active pressure shall not be less than 0.25 times the effective overburden pressure at any depth, or 0.035 ksf/ft of wall height, whichever is greater (AASHTO 2014). For soft to medium-stiff clays, lateral loads are typically governed by the undrained (total stress) strength properties as outlined within AASHTO Section 3.11. Information regarding evaluation of effective and total stress strength properties of cohesive soils is included in GEC-5 (Loehr et al. 2016). If hydrostatic pressure behind the wall cannot be relieved using a drainage medium behind the lagging or panel fascia, water pressure must be added to that of earth pressure (with submerged unit weights for earth pressure. Download 6.03 Mb. Share with your friends:
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