Development and Preliminary Testing of a New Robotic Tool for Direct Determination of ‘P-Y’ Soil Reaction Curves for Offshore Geotechnical Applications

Monopiles are the most widespread foundation option for offshore wind turbine foundations and their design is largely governed by lateral stability and serviceability. The determination of lateral soil reaction ‘p-y’ curves is a crucial element for their design. At present, ‘p-y’ curves are typically determined through indirect methods, such as correlation from fundamental constitutive parameters, CPT data or extracted through numerical procedures. This paper presents the specification requirements, initial mechanical design, sensor calibration and preliminary testing in a small calibration chamber of a new robotic site investigation tool, the ROBOCONE ‘p-y’ module. This new device can be fitted behind a standard CPT cone. It features a cylindrical module that, after insertion in the ground, can move sideways to closely mimic the kinematic mechanism experienced by a laterally loaded pile element and provide direct “in-situ” characterisation of the ‘p-y’ soil reaction curves. The imposed horizontal translation is substantially different from those of the typical pressuremeter and dilatometer, and analogous to that of a small laterally loaded pile. Movements of the module can be programmed to apply simple monotonic lateral loading conditions and complex stress-controlled or deformation-controlled histories (i.e. cyclic loading, consolidation stages, maintained load). These provide data that can be scaled directly to support advanced cyclic and whole-life design procedures for the lateral ‘p-y’ response of piles.