The foundation of fixed offshore platforms located in the Bay of Campeche, Mexico in shallow waters consist of open-ended driven pipe piles with a diameter between 36?h (0.914 m) and 84?h (2.134 m), and pile lengths between approximately 60 m and 115 m below seafloor and the ultimate axial pile capacity have been estimated using the standard alpha method (in clay) and the beta method (in sand) presented in the recommended practice of the American Petroleum Institute RP2GEO (API, 2011). This guideline and ISO 19902 (ISO, 2007) also include four new CPT-based methods for calculating the ultimate axial capacity in silica sands. This paper presents the evaluation of ultimate axial pile capacity using the four CPT-based methods developed by UWA, NGI, Imperial College and Fugro in sand and corresponding clay methods and compare the results with ultimate axial pile capacity obtained with the standard API-11 method at 39 platform locations in the Bay of Campeche in water depths between 14 m to 215 m, and divided according to the predominant soil type: 1) 10 clay profile sites, 2) 6 clay profile sites with some sand layers, 3) 14 profile sites stratified with clay and sand strata, and 4) 9 sand profile sites with some clay layers. The results of the analyses in a clay site showed that similar magnitude and tendency to the API method to depths up to 50 m, however, beyond this depth the API-11 method and the NGI-05 method exhibited greater magnitudes compared to the ICP-05 and Fugro-11/05 methods. Similarly, on stratified (sand and clay) and sand profiles, the API-11 and NGI-05 methods showed greater axial capacities than ICP-05, Fugro11 and UWA-05 methods, presenting a smaller difference than in clayey soils. The relation /sup Q/supC//[CPT-Method]//sup Q/sup C//[API-11]) for all CPT-based methods to depths greater than 25 m, present a lower and upper limit of approximately 0.8 and 1.2, respectively. For depths up to 25 m, the relation /sup Q/supC//[CPT-Method]//sup Q/sup C//[API-11]) for most cases resulted in a greater magnitude and is attributed to uncertainties in the resistance measurements of shallow soils.
Ivan Zarate, Francisco A. Flores, President and Diego Cruz
Keywords: axial capacity, driven piles, CPT-based methods
Publisher: DFI