The bearing capacity of piles consists of both base resistance and side resistance. The side resistance of piles is in most cases fully mobilized well before the maximum base resistance is reached. As the side resistance is mobilized early in the loading process, the determination of pile base resistance is a key element of pile design. Static cone penetration is well related to the pile loading process, since it is performed quasi-statically and resembles a scaled-down pile load test. In order to take advantage of the CPT for pile design, load-settlement curves of axially loaded piles bearing in sand were developed in terms of normalized base resistance (qb/qc) versus relative settlement (s/B). Although the limit state design concept for pile design has been used mostly with respect to either s/B = 5% or s/B = 10%, the normalized load-settlement curves obtained in this study allow determination of pile base resistance at any relative settlement level within the 0 – 20% range. The normalized base resistance for both non-displacement and displacement piles were addressed. In order to obtain the pile base load-settlement relationship, a 3-D non-linear elastic-plastic constitutive model was used in finite element analyses. The 3-D non-linear elastic-plastic constitutive model takes advantage of the intrinsic and state soil variables that can be uniquely determined for a given soil type and condition. A series of calibration chamber tests were modeled and analyzed using the finite element approach with the 3-D non-linear elastic-plastic stress-strain model. The predicted load-settlement curves showed good agreement with measured load-settlement curves. Calibration chamber size effects were also investigated for different relative densities and boundary conditions using the finite element analysis. The value of the normalized base resistance qb/qc was not a constant, varying as a function of the relative density, the confining stress, and the coefficient of lateral earth pressure at rest. The effect of relative density on the normalized base resistance qb/qc was most significant, while that of the confining stress at the pile base level was small. At higher relative densities, the value of qb/qc was smaller (qb/qc = 0.12 -0.13 for DR = 90%) than at lower relative densities (qb/qc = 0.19 - 0.2 for DR = 30%). The values of the normalized base resistance qb/qc for displacement piles are higher than those for nondisplacement piles, being typically in the 0.15 - 0.25 range for s/B = 5% and in the 0.22 - 0.35 range for s/B = 10%. The values of the normalized base resistance qb/qc for silty sands are in the 0.12 – 0.17 range, depending on the relative density and the confining stress at the pile base level. The confining stress is another important factor that influences the value of qb/qc for silty sands. For lower relative density, the value of qb/qc decreases as the pile length increases while that for higher relative density increases. For effective use of CPT-based pile design methods in practice, the method proposed in this study and some other existing methods reviewed in this study were coded in a FORTRAN DLL with a window-based interface. This program can be used in practice to estimate pile load capacity for a variety of...

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piles, sands, cone penetration test, bearing capacity, constitutive model, finite element analysis, limit states design, calibration chamber test, SPR-2142

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

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