Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Block 4 - Plan and Execute a Subsurface Investigation and Testing Program
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- Block 5 - Characterize Subsurface Conditions
- Block 6 - Selection of Deep Foundation Type
| Block 4 - Plan and Execute a Subsurface Investigation and Testing Program Based on the results of Blocks 1, 2, and 3, a subsurface investigation program can be planned and performed to obtain the information necessary to characterize the geotechnical conditions and develop design parameters. The performance of the subsurface investigation program maybe done in multiple stages, such as a preliminary investigation followed by more detailed investigation, or a supplemental investigation maybe performed later in design to verify initial findings or obtain more detailed data for finalizing the design. This is especially true for design-build contracts where an initial investigation is performed for the development of the preliminary design for the procurement documents, followed by a final investigation for final design by the design-builder. In design-build projects, and often for design-bid-build projects, the locations of structure foundations are not known or finalized at the time that the initial subsurface investigation is performed. Block 5 - Characterize Subsurface Conditions The results of the subsurface investigation and testing program are used to characterize the subsurface conditions for analysis of laterally loaded deep foundations. A subsurface stratigraphy and profile should be developed for the site for use in design, including soil layers, rock layers, and groundwater levels. Subsurface parameters should also be developed along with inputs for individual soil and rock units for lateral pile analysis. Note that stratigraphy and parameters developed for lateral pile analysis may differ from that used for axial foundation analysis. Block 6 - Selection of Deep Foundation Type Understanding the project needs (Block 1), loads (Block 3), and subsurface conditions (Block 5), select a deep foundation type for preliminary selection. In some cases, the foundation type maybe decided based on local practice or standards regarding similar types of structures or by structural design and connection considerations. In other cases, there maybe several viable alternatives that may need to be evaluated in more detail. In selecting the type of deep foundation, consideration should be given to Lateral load capacity Lateral soil displacements Subsurface conditions and their impact on constructability Proximity of adjacent structures Low headroom Noise and vibration restrictions Availability of local contractors Project size/number of foundation elements • Corrosivity of site soils Whether the work is over water Others 53 Determination of the foundation type often requires a significant amount of engineering judgment and should be performed by engineering professionals with sufficient experience in this field. In some cases, more than one foundation type maybe feasible and additional considerations, such as economics and relative risks, will need to be considered. It maybe possible that two or more foundation types are considered for preliminary analyses or evaluations. Axial load capacity may also influence or control the selection of the foundation type. Considerations of axial loading will be needed if axial loads area significant aspect of the design. For complex projects or design-build projects, the process of selection of the deep foundation type and size may require iterations as the subsurface conditions are more thoroughly characterized during later stages of design or as the loading conditions are more fully developed. Download 6.03 Mb. Share with your friends:
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