Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
DESIGN PROCESS AND TEAM ROLES FOR ANALYSIS OF LATERALLY
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| 5 DESIGN PROCESS AND TEAM ROLES FOR ANALYSIS OF LATERALLY LOADED DEEP FOUNDATIONS This chapter provides an overview of the design procedure for laterally loaded deep foundations and team roles for geotechnical and structural engineers during the design process. The design procedures are intended to focus on procedures and considerations specific to laterally loaded deep foundations. This is not intended to be a comprehensive description of design procedures for all aspects of deep foundation design rather this section focuses on design for lateral loading only. Refer to other references, such as Hannigan et al. (2016), Brown et al. (2010), Brown et al. (2007), and Sabatini et al. (2005) for further details on the design of driven piles, drilled shafts, CFA piles, and micropiles, respectively. Although the design procedure is presented as a step-by-step process, in practice it often does not follow a linear path. The size and scope of the project, contracting approach, and complexity of the foundation loadings (lateral load demand as well as axial loads) affect the actual progression of tasks. The design process often includes multiple iterations in order to refine the design, incorporate additional subsurface data or testing information, accommodate design changes, or address constructability considerations. The design procedure presented herein is intended to provide a logical general design procedure to enable the designer to consider the necessary steps for adequate lateral pile design and analysis the actual progression of the steps may vary. The design procedure is illustrated in Figure 5-1. Similarly, the roles of design engineers presented herein are general roles that are common in practice, but may differ for individual projects based on the type of project, complexity of the work, local practice, contract approach and responsibilities, and the experience of the individual designer. 5.1 DESIGN PROCESS Block 1 – Establish Project Type, Performance Requirements, and Constraints The first step in the process is to define the type of project and project needs, including the need for laterally loaded deep foundations. 1. Establish the general structure requirements. Is it anew bridge, replacement bridge, retaining wall, noise wall, slope stabilization, signor light post, etc 2. Identify and define projector site conditions that may impact the selection of deep foundation type or construction, especially regarding selection of deep foundation type and lateral loading considerations. Examples include limited right-of-way, constrained site areas or access, overhead constraints, potential for scour, potential for construction over bodies of water (construction considerations for foundation type selection, potential for lateral loads due to waves or vessel impacts, etc, wetlands or other areas with environmental restrictions, existing or adjacent structures, restrictions regarding vibrations, etc. 3. Identify the general structure layout and site grades, surficial site characteristics, and general geology. 4. Identify any special design events or considerations, such as seismic, scour, downdrag, vessel impacts, etc. 5. Determine preliminary load types and estimates (even order of magnitude) to aid in determining whether deep foundations maybe needed and whether lateral loads will be a significant design consideration. 48 6. Determine load factors for the applicable load types and resistance factors for Strength, Service, and Extreme Event Limit States. As indicated in Chapter 4, Strength Limit States will be defined based on the factored load combinations for design. Multiple load combinations may need to be assessed unless a single, most critical load combination can be identified. Service Limit States include tolerable deflections and/or global stability using service limit loads. Global stability requirements for retaining walls or slope stabilizations should consider consequences of failure in the selection of the resistance factors as discussed in Section 4.6. 7. Define lateral foundation design performance criteria. This may include limiting deflection values, a maximum factored resistance, and/or achievement of a maximum resistance against global stability in the case of slope stabilization or retaining walls. In some cases, it will be known at the early stages of a project that deep foundations will be needed and will be subject to lateral loads that are significant enough to control the overall foundation design. Examples of this type of project include noise walls, continuous retaining walls for excavation support, or retaining walls or deep foundations for slope stabilization. In other cases, it may not be evident at this stage that laterally loaded deep foundations will be needed. For example, anew bridge or bridge replacement in an area where rock or dense soils are relatively shallow, especially if an existing bridge is on shallow foundations. It may not be evident that the new bridge will need deep foundations until other aspects of the project are better defined, such as the structure loads, strength of surface materials, scour depth, seismic loads, etc. The steps that follow assume that deep foundations with lateral loads are expected. |