Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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Soldier Rev B
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- 6.3.3 Limitations
| 6.3.2 Factors Affecting P-y Curves P-y curves are described as a set of expressions to capture the three portions of the curve described above. Most p-y curves were derived from horizontal load tests conducted on full-scale deep foundation elements installed in more or less uniform soil conditions and under a particular loading condition. Some p-y curves are based on in-situ test results. In addition, p-y curves can be derived using the strain wedge model (SWM), which is described in a later section. P-y curves are largely empirical and are affected by a number of factors, including but not limited to • Geomaterial properties – Undrained and drained strength i. Undrained Shear Strength (S u ) ii. Friction Angle (φ) – Stress-strain behavior iii. Poisson’s ratio (ν) iv. Strain (ε50) v. Subgrade Modulus (k) vi. Elastic Modulus (E) – Unit weights for soil and rock – Rock mass properties – Intact rock properties 74 Subsurface conditions – Depth to groundwater – Homogeneous or layered profile – Depth to rock Size and stiffness of deep foundation elements Type of loading (static, dynamic, or cyclical) Liquefaction of soil Head fixity Sloping ground surface In some cases, several factors will act in combination to affect the p-y curve, such as cyclical loading of cohesive soils. A more detailed discussion and specific examples of p-y curves are presented in Appendix A. 6.3.3 Limitations A limitation of the p-y method is that it is a one-dimensional solution it does not directly account for D effects of the loading of the soil mass, although the empirically derived curves from load tests are based on actual three-dimensional field tests. Another significant limitation of the p-y approach is that it is mostly empirical and difficult to adapt to new conditions if empirical data are not available. Soil parameters used in this method are not fundamental parameters therefore, parameters obtained with conventional laboratory tests, such as triaxial tests, cannot always be linked in a straightforward manner to those that are used in development of p-y curves. In addition, p-y methods are generally more applicable to deep foundations that are relatively long and slender, and as a result, can bend and deflect, i.e., structural failure of the deep foundation element in bending usually controls. The p-y methodology is not fully applicable to short piles/shafts that tend to rotate, where soil failure near the ground surface controls. Also, care must be used for large diameter elements, such as large diameter drilled shafts, because the majority of published curves were developed based on smaller diameter elements. Download 6.03 Mb. Share with your friends:
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