Development of a model jack-up unit for the study of soil-structure interaction on clay

Abstract

The behaviour of spudcan footings under combined vertical, moment and horizontal loading is a critical aspect of the site-specific assessment of offshore jack-up platforms. In recent years, experiments on single footings have helped describe the non-linear load-displacement behaviour of spudcans on various soil types, and this behaviour has in turn been encapsulated numerically, typically in the form of semi-empirical models based on strain-hardening plasticity theory. There is cause for concern, however, that the application of these models in predicting the behaviour of a complete jack-up unit with multiple footings has yet to be verified experimentally. To achieve this, and to gain an improved understanding of the overall system behaviour under various loading regimes, a 1:250 scaled model of a representative jack-up unit has been designed, built and calibrated at The University of Western Australia (UWA). The model can be used to perform sophisticated 1-g pushover tests (both monotonic and cyclic) in which all key forces, moments and movements of the jack-up unit, including spudcan loads and displacements, are continuously monitored. Initial testing has been performed on reconstituted samples of soft overconsolidated kaolin. This paper discusses the design and development of the apparatus, its calibration and verification, the procedures used during a test, and the methods used to prepare and characterise the kaolin samples. General experimental aims are discussed, and aspects of the structural and geotechnical scaling are considered in detail. Some example results from a monotonic pushover test are presented to illustrate the capabilities of the system.