Design of foundations bearing in sand based on CPT results

The bearing capacity of piles consists of both base resistance and side resistance. 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). 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. 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. 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/q c was most significant, while that of the confining stress at the pile base level was small. The values of the normalized base resistance q b/qc for silty sands were also addressed. Vertically loaded footings on sands were also modeled using the finite element method with the non-linear stress-strain model. The load-settlement responses obtained from these analyses were compared with those from an existing elasticity-based method. The application of cone penetration testing to footing design was investigated based on the results of the analyses