Figure 6-5: Model of a deep foundation element under lateral loading conditions showing concept

71 The software analysis involves the simultaneous solution of a series of equations numerous times. The general process within the software analysis consists of assuming a deflected shape of the deep foundation element (initial deflection, obtaining k values from the p-y curves based on the initial deflections, solving the equations to determine anew set of computed deflections, and repeating the process with multiple iterations until the initial deflections and computed deflections are within a specified tolerance. Once the p-y analysis has finished, the bending moment, shear, and slope of the deflection can be calculated from the results using Equations 6-2 through 6-4. Graphical and tabular outputs of the displacement, shear, moment, slope, and soil resistance can be generated from the results of the analysis. The ability of the analysis above to accurately predict the behavior of a deep foundation element under lateral loading is dependent on the ability to represent the soil response by an appropriate set of p-y curves. The p-y curves available in commercial software programs have been largely empirically developed based on the results of full-scale lateral load tests and experiments. The p-y method is therefore predominantly an empirically based design method rather than a fundamentally theoretical method. The software analysis for the p-y method is generally easy to use and produces results quickly. This provides the user the opportunity to investigate a large number of variables and their potential impact on the design with relative ease. This can include investigating variations on loading conditions (magnitude, type, and location of loads, subsurface conditions (soil or rock layer depth, thickness, density, strength and groundwater depth, and geometry (ground slope, foundation embedment, and exposed height of foundation element, among other factors. The analysis of deep foundations using the p-y method should include parametric evaluation of key input parameters in order to assess the potential sensitivity of the results to such inputs. This will help identify which parameters maybe most critical and to what degree, which may influence the decision to require additional field investigation and testing, selection of foundation type, construction testing, or other aspects of the design. Most commercial software programs include a wide variety of p-y curves for various geomaterials, allowing the practitioner to reasonably model real-world conditions. However, there are limitations with applying the available models to conditions that do not match those upon which the models were originally based the subsurface conditions (soil, rock, and groundwater conditions, foundation characteristics (foundation type, material, shape, and size, and loading conditions (static, cyclical, loading rate) used in the experiments versus the problem condition should be understood to appreciate how applicable the p-y curves are and what inherent risks in the analysis and design maybe present as a result. The p-y method can be used to develop site-specific or project-specific p-y curves based on lateral load tests, as discussed in Chapter 12 and Appendix C. New or updated p-y curves are frequently being developed and published, or included in updated software versions, as a result of new research and developments in the industry.

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