Evaluation of Curve Fitting Techniques in Deriving p–y Curves for Laterally Loaded Piles

© 2016 The Author(s)The p–y method is one of the most popular methods for the analysis and design of laterally loaded piles. The mathematical relationship it provides between the bending moment, which can be easily measured at strain gauges along the pile, and the soil resistance and lateral pile displacement, facilitates the construction of p–y curves. Numerical techniques are required to fit smooth continuous curves to the discrete bending moment data in order to improve the accuracy of subsequent differentiation and integration operations. Due to the lack of guidance on the optimum positioning of strain gauges and the reliability and accuracy of curve fitting methods, a unifying study, inclusive of small (0.61 m) and large (3.8 and 7.5 m) diameter piles in clay, was carried out using 18 strain gauge layouts and cubic spline, cubic to quintic B-spline and 3rd to 10th degree global polynomial techniques. Bending moment data was obtained using 3D finite element analysis. Through a comprehensive evaluation, the cubic and cubic B-spline methods were found to be consistently accurate in deriving p–y curves for both the small and large diameter piles

Evaluation of the p-y method in the design of monopiles for offshore wind turbines

Monopile foundations, currently designed using the p-y method, are technically viable in supporting larger offshore wind turbines in waters to a depth of 30 m. The p-y method was developed to better understand the behavior of laterally loaded long slender piles required for the offshore oil and gas installations. The lateral load-deformation behavior of two monopiles, 5 and 7.5 m dia, installed in soft clays of varying undrained shear strength and stiffness, was studied. A combination of axial and lateral loads expected at an offshore wind farm location with a water depth of 30 m was used in the analysis. It was established that the Matlock (1970) p-y curves are too soft and under-estimate the ultimate soil reaction at all depths except at the monopile tip. At the pile tip, the base shear was not accounted for in the p-y curves, hence resulting in the over-estimation of the soil reaction. Consequently, the Matlock (1970) p-y formulation significantly underestimates the monopile ultimate lateral capacity. The use of the Matlock (1970) p-y method would result in over-conservative designs of monopiles for offshore wind turbines. This is an abstract of a paper presented at the Offshore Technology Conference (Houston, TX 5/6-9/2013)

Evaluation of Curve Fitting Techniques in Deriving p–y Curves for Laterally Loaded Piles

© 2016 The Author(s)The p–y method is one of the most popular methods for the analysis and design of laterally loaded piles. The mathematical relationship it provides between the bending moment, which can be easily measured at strain gauges along the pile, and the soil resistance and lateral pile displacement, facilitates the construction of p–y curves. Numerical techniques are required to fit smooth continuous curves to the discrete bending moment data in order to improve the accuracy of subsequent differentiation and integration operations. Due to the lack of guidance on the optimum positioning of strain gauges and the reliability and accuracy of curve fitting methods, a unifying study, inclusive of small (0.61 m) and large (3.8 and 7.5 m) diameter piles in clay, was carried out using 18 strain gauge layouts and cubic spline, cubic to quintic B-spline and 3rd to 10th degree global polynomial techniques. Bending moment data was obtained using 3D finite element analysis. Through a comprehensive evaluation, the cubic and cubic B-spline methods were found to be consistently accurate in deriving p–y curves for both the small and large diameter piles

Enhancing the lateral capacity of monopiles in sand using reinforced concrete footings

This paper presents the results of three dimensional finite element analyses, which investigated the improvement in the lateral capacity of a large diameter monopile in medium dense to dense sand when used in combination with reinforced concrete footings. Footings, with and without a skirt, were assessed under a combination of vertical, lateral and moment loads expected at an offshore wind farm location with a water depth of 30 m. The influence of surcharge load due to a gravel armour was also examined. Findings indicate favourable interaction between the monopile, footings and the gravel armour resulting in increased lateral capacity of the hybrid systems. The larger lateral capacity is as a result of the restoring force provided by the footings and the subsequent reduction in monopile bending moments. In addition to being technically feasible, the hybrid options were also found to be cost effective

Cyclic lateral loading of monopiles for offshore wind turbines

This paper presents the results of implicit three dimensional soil-pore fluid finite element analyses investigating cyclic lateral loading on a 3.8mdiameter monopile in London Clay.The cyclic behaviour of the clay was simulated using the subloading tij constitutive model.Two-way and one-way cyclic lateral loads, representing offshore wind turbine production loading conditions, were applied to the monopile. Both cyclic loads were found to cause progressive accumulation of pile lateral displacement and rotation at mudline. However, the one-way load induced greater cumulative pile deformation in comparison to the two-way load.With each cycle, the rate of accumulation attenuated indicating an increase in the cyclic clay stiffness. A gradual increase in the pile shear force and bending moment, and low magnitude excess pore pressure build-up in the clay over each cycle, provided further verification of cyclic clay hardening

Lateral response of monopiles using centrifuge testing and finite element analysis

Offshore wind capacity is expected to grow exponentially over the next decade resulting in the production of a considerable amount of renewable energy. Monopiles are currently the most popular type of foundation for supporting offshore wind turbines in shallow to medium depth waters. In this paper, the load-deformation response of a 3.8 m diameter monopile installed in soft clays when subjected to axial and lateral loading is investigated using centrifuge testing and soil pore-fluid coupled three-dimensional finite element analysis. Monopile deformation is principally assessed in terms of its lateral displacements and bending moments. Its behaviour as a short rigid pile is discussed using concepts such as its rotation at mudline and the pile depth at which pivoting occurs. © 2014 Taylor & Francis Group