Influence of layered soil profiles on the application of p-y curves for large diameter monopiles

Abstract

The use of p-y curves in a two-layered clay profile is explored in this study using 3D finite element analyses (FEA) for large diameter monopiles with short lengths. The lateral net soil resistance-deflection (p-y) curves and ultimate capacity (pult) extracted from the layered profiles were compared with the homogenous soil models. It was observed that pult above 0.5 diameters from the layer boundary was unaffected, pult immediately above the layer boundary increases in soft over stiff clay and reduces in stiff over soft clay, whilst pult below the layer boundary differs from the homogenous case. When using FEA derived p-y curves from the homogenous case to represent the two-layered profile in a beam-spring calculation, lateral pile capacity was under predicted by up to 18%. It is concluded that the use of p-y curves derived from homogenous soils can lead to over conservative capacities for layered profiles, especially when using methods not suitable for piles with low L/D ratios. Implementation of 3D models may be necessary for optimization or for deriving more reliable p-y curves. The analyses were carried out using hardening soil model input parameters for Bangkok clays.