A framework for the design of vertically loaded piles in spatially variable soil

• Published in: Computers and geotechnics 2021-06, Vol.134, p.104140, Article 104140
• Main Authors: Cai, Yongmin, Bransby, Fraser, Gaudin, Christophe, Uzielli, Marco
• Format: Article
• Language: English
• Subjects: Coefficient of variation; Cone penetration tests; Design; Design factors; Design modifications; Failure analysis; Field theory; Fields (mathematics); Load distribution; Load distribution (forces); Mathematical analysis; Ocean floor; Offshore; Offshore energy sources; Offshore operations; Pile capacity; Piles; Probability theory; Reliability; Reliability analysis; Risk and probability analysis; Soil; Soil investigations; Soils; Spatial variability; Spatial variations; Statistical analysis; Statistical methods; Statistical tests; Stress concentration; Vertical distribution; Vertical loads; Wind farms; Wind power
• ISSN: 0266-352X; 1873-7633
• DOI: 10.1016/j.compgeo.2021.104140

Each pile in an offshore wind farm may be designed solely on the results of a single cone penetration test (CPT) positioned at its center or based on sample statistics calculated from multiple investigated locations in the same geotechnical unit. This study investigates quantitatively the effects of spatial variability of soil on the efficacy of the two approaches to achieve a reliable design. Random field theory is used to generate sets of cone tip resistance profiles with different characteristics to represent different seabed conditions and piles are ‘designed’ using the above two approaches and the partial factor method to withstand a given vertical drained design load distribution. The effects of the inaccuracies in prediction of pile capacity from the CPT data are quantified in terms of the scatter in calculated reliability (or probability of failure). Outputs of the parametric statistical analysis demonstrate that the ability of the two CPT-based approaches to produce a reliable foundation design is dependent on the ratio between the horizontal scale of fluctuation and the pile diameter, and the overall variability (coefficient of variation) of the seabed properties. Modifications to deterministic, partial factor design approaches are suggested to account for these uncertainties to ensure target reliabilities are achieved.