Abstract
This paper describes the results obtained from a field testing campaign on laterally loaded monopiles conducted at Cowden, UK, where the soil consists principally of a heavily overconsolidated glacial till. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained for monotonic loading tests on piles of three different diameters (0·273 m, 0·762 m and 2·0 m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. The tests included the application of monotonic loading incorporating periods of constant load to investigate creep effects, and investigations on the influence of loading rate. Data are presented on measured bending moments and inclinations induced in the piles. Inferred data on lateral displacements of the embedded section of the piles are determined using an optimised structural model. These field data support the development of a new one-dimensional modelling approach for the design of monopile foundations for offshore wind turbines. They also form a unique database of field measurements in an overconsolidated clay, from lateral loading of piles at a vertical distance above the ground surface.
Highlights
A study has been completed, employing field testing and three-dimensional (3D) finite-element modelling, to develop a new design approach for monopile foundations for wind turbine support structures in North Sea waters
This paper describes the field testing conducted as part of the PISA study on a set of reduced-scale monopiles at a test site at Cowden in the UK
A key driver for the PISA field testing programme was to explore pile response in typical North Sea soils; this led to the choice of the stiff glacial clay till site at Cowden for the test programme
Summary
A study (referred to as PISA) has been completed, employing field testing and three-dimensional (3D) finite-element modelling, to develop a new design approach for monopile foundations for wind turbine support structures in North Sea waters. The well-established ‘p–y’ method for the analysis of laterally loaded piles in clay, for example, was developed principally from pile tests conducted at two soft clay sites by Matlock (1970). Kaolin clay samples are typically used, being a well-established benchmark soil, with a well-described constitutive response These materials have constitutive behaviours that are different from North Sea clays, which tend to be dominated by overconsolidated stiff tills. A key driver for the PISA field testing programme was to explore pile response in typical North Sea soils; this led to the choice of the stiff glacial clay till site at Cowden for the test programme. The tests: (a) employed modern instrumentation, monitoring and loading systems to produce high-quality data for a range of test configurations; (b) addressed the typical geometric loading conditions for wind turbine monopiles; (c) focused on soil conditions at North Sea wind farm sites; (d ) contributed test data at a credible scale to provide confidence in the application of the results
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