Concept design of a new CPT module for direct in situ measurement of p-y soil responses

Due to the rapid expansion of the offshore energy market, driven by the installation of wind turbines founded on single-or multi-piled foundations, the design and optimisation of laterally loaded piles has attracted enormous interest in the last decade. Current industrial design practice, for offshore and onshore piles, typically employs lateral load-displacement springs (p-y) to model the soil response under serviceability, ultimate or fatigue limit state scenarios of this foundation type, supplemented by moment and axial springs. Correlations based on CPT data are commonly used to determine soil properties and, in turn, the stiffness and resistance of the p-y reaction curves, in advance of detailed laboratory testing that follows later in the project schedule. To extend the potential for in situ testing to support lateral pile design, this paper presents the novel idea of complementing a CPT device with a new module capable of probing the soil in such manner that the monotonic and cyclic p-y soil response (including its evolution during the foundation design life) can be directly measured in the field. The stress and strain fields induced by such a module resemble those of a miniature laterally loaded pile element and differ from circular or flat cavity expansions induced by pressuremeters or dilat-ometers. The new device will be developed in a collaborative research project ‘ROBOCONE’ financed by the UK and Irish research councils. The background thinking and initial conceptual design of the device, including the review and selection of appropriate motion mechanisms and instrumentation, is presented in this manuscript.