Evaluation of Penetration Resistance of Spudcan Foundations in South-West Coastal Areas of Korea

Abstract

The jack-up barges are widely used to construct wind turbines in hostile offshore environments. The jack-up barges acquire the stability required for such operations by lowering three to four legs into the subsea soil, which are connected to spudcan foundations. Assessing the penetration resistance of spudcans is essential for safe operation of jack-up barges. However, the applicability of empirical equations to estimate the peak resistance for Korean subsea soil profiles, which most often consist of alternating layers of sands, silts, and clays, have not yet been evaluated. In this study, extensive borehole measurements performed at south-west coastal area of Korea were obtained and analyzed. It is shown that the profiles mostly consist of sand - clay (silt) - sand layers. The 3D finite element (FE) analyses were performed using the commercial code ABAQUS to extract the penetration resistance profiles of spudcan foundations. The sand and clay layers were modeled using the linear elastic-perfectly plastic models following Mohr-Coulomb and Tresca failure. The coupled Eulerian-Lagrangian (CEL) approach was used to simulate the large deformations that occur in the soils during the penetration. The outputs from the numerical analyses were compared with the results from the empirical Hu et al. (2014) method, which predicts the resistance profile for sand over clay profiles. Results show that the empirical procedure is applicable for profiles where clay layer thickness exceeds the diameter (D) of the spudcan foundation. However, the empirical method underestimates the resistance of the clay profile for clay layers thinner than 2/3D. The resistance increases abruptly at a depth of 2/3D from the bottom of the clay-sand interface, most likely because of the sand plug below the spudcan influences the resistance. The comparisons reveal that the empirical procedure provides unconservative estimate of the resistance. The use of the 3D numerical model is recommended for accurate estimation of the resistance.