Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Block 7 - Determine Initial Foundation Layout and Head Fixity Conditions
Download 6.03 Mb. View original pdf
|
Soldier Rev B
- Navigate this page:
- Block 8 – Estimate Pile Size and Depth and Determine Subsurface Conditions for Lateral Loading Analysis
| Block 7 - Determine Initial Foundation Layout and Head Fixity Conditions Based on the selection of the foundation types) and the characterization of the subsurface conditions, the structure type and geometry are advanced far enough to determine an initial foundation layout, including fixity condition. For example, if a retaining wall or abutment is a cantilever wall supported on piles, the size of the footing maybe established along with estimated pile size, spacing, and number of piles within the group. The spacing between foundation elements may impact the available soil resistance for analysis through shadowing or overlapping areas of influence under lateral loads. This is discussed more in Chapter 7 regarding analyses of groups of deep foundation elements. Often the design will be started assuming no reduction incapacity is needed based on spacing and maybe refined later as the foundation layout is finalized. At this stage of design, it may also be determined whether the pile head will be sufficiently fixed within a cast-in-place footing (pile cap, or whether it will be a free head condition that is allowed to rotate. This will be needed for some computer analyses. A free head condition is appropriate for single or isolated pile/shaft foundations and a fixed head fora foundation with multiple rows of piles/shafts. This assumption can be revised if necessary during the design process. This approach will likely reflect the final design conditions. Block 8 – Estimate Pile Size and Depth and Determine Subsurface Conditions for Lateral Loading Analysis Based on the selected foundation type and layout and the characterization of subsurface conditions, develop an estimate of the pile size and depth and determine the subsurface profile for lateral load analysis. The pile size includes an estimate of the minimum pile width or diameter. A minimum depth for analysis should be determined based on considerations regarding the subsurface profile for each load case. In many cases, the estimate of pile size and depth will bean initial trail size that is analyzed and refined, either increased or decreased, until a suitable design is determined that satisfies the project performance criteria. 54 A specific subsurface profile for analysis should be developed for each lateral load case to be analyzed. This should include considerations for the variability of subsurface stratigraphy and parameters at different foundation locations. Other design considerations that may impact the subsurface profile and parameters should also be considered. These include scour depth, liquefied soil layers during seismic events, additional soil layers (fill) due to proposed construction, compression of soft layers due to proposed fill, etc. The design for laterally loaded deep foundations will often include consideration of scour conditions, which must be assessed for the design flood and the check flood. The design flood is typically a year flood and is considered under the strength and service limit conditions. The check flood is typically a larger interval, up to a year interval, and is considered under the Extreme Event Limit State. Consideration of scour events may alter the geotechnical subsurface profile used in analyses rather than the actual loads, resistances, or applied load or resistance factors. Download 6.03 Mb. Share with your friends:
|