Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
LATERAL LOAD APPLICATIONS AND SELECTION OF DEEP FOUNDATION
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| 2 LATERAL LOAD APPLICATIONS AND SELECTION OF DEEP FOUNDATION TYPE FOR TRANSPORTATION PROJECTS This chapter provides an overview of laterally loaded deep foundations commonly used in transportation projects. 2.1 LATERAL LOAD APPLICATIONS FOR TRANSPORTATION PROJECTS 2.1.1 Typical Lateral Load Applications for Vertical Deep Foundations Lateral loads in transportation projects can originate from a variety of sources including vehicle acceleration and braking on bridge decks and approaches wind effects on traffic, on bridge decks, and/or structures wave and current action in rivers and streams on bridge piers forces caused by debris and ice floating in watercourses thermal effects (e.g., in integral abutments vessel/vehicle impact on bridge piers and abutments earth pressures acting behind abutment or retaining walls slope movements and seismic events. In some cases, the magnitude of lateral loads maybe of comparable magnitude to that of axial loads. Examples of situations when deep foundations are used to resist lateral loads include bridge abutments (Figure abridge piers (Figure b temporary excavation support (Figure 2-2); permanent retaining walls (Figure 2-3); noise barrier walls (Figure 2-4); slope or landslide stabilization (Figure 2-5); and signs and traffic signals. Lateral loads caused by traffic, braking, and wind forces along the longitudinal and transversal directions of abridge can act on abridge pier as shown in Figure 2-6 in addition to vertical loads. In the case of bridge abutments, loads due to lateral earth pressures must be added to the lateral loads from the bridge structure. Bridge pier foundations maybe either a single deep foundation element, such as a large diameter drilled shaft, or maybe a group of deep foundation elements such as a group of piles, drilled shafts, or micropiles. Lateral earth pressures generated behind temporary and permanent retaining structures can be resisted using deep foundations. Conventional cantilever retaining walls maybe supported by piles similar to abridge abutment. Cantilever or non-gravity retaining walls can support lateral loads from retained earth using soldier piles, secant piles, or tangent piles. The lateral retained earth loads are supported by a combination of passive resistance of the portion of the piles that is embedded below grade and the structural capacity of the piles. If additional lateral capacity is needed, external braces or tieback anchors can be incorporated into on-gravity wall systems. Figure 2-7 suggests that a vertical deep foundation used to stabilize slopes resists lateral loads above the potential slip surface and transfers this load to the ground below the potential slip surface. Lateral earth pressures above the slip surface are destabilizing and those below the slip surface are stabilizing. In the case of foundations for sound walls, traffic signals, and signs, lateral loads are most commonly caused by wind action and these are typically resisted by a single element, such as a drilled shaft (Figure 2-8) or occasionally a group of piles or small diameter drilled shafts. |