Lateral bearing factors and elastic stiffness factors for robotic CPT p-y module in undrained clay

There is a strong incentive to enhance in-situ ground characterisation tools to provide additional data that supports early infrastructure design in engineering projects, prior to completion of laboratory element testing on borehole samples. Advances in robotic technology allow additional soil deformation modes to be probed by integrating a cylindrical section of cone capable of horizontal translation into an expanded standard cone penetrometer, referred to here as ROBOCONE p-y module, which can mimic the load and displacement behaviour of laterally loaded pile element. This paper presents a series of three-dimensional elasto-plastic finite element simulations and semi-analytical upper bound analyses of this p-y module in homogeneous, undrained clay. The aim is to support the optimal choice of p-y module geometry and to lay the foundation of an interpretation method. In particular, the paper investigates the lateral bearing factor (NRC) and elastic stiffness factor (KRC) required for the measured load–displacement curves to be converted into practical design soil parameters such as undrained shear strength and elastic shear modulus. The numerical results reveal that NRC varies inversely with the height-diameter ratio (HR/DR) of the p-y module and interface roughness, and these factors are compared to semi-analytical upper-bound solutions. Correction factors that allow for the finite length of the p-y module are derived, and these have minimal variation with interface roughness. The height-diameter ratio HR/DR has a similar influence on KRC. Simple mechanism-based expressions for the lateral bearing and stiffness factors are devised to generalize the numerical results and provide definitive solutions to determine soil undrained strength and elastic stiffness from ROBOCONE p-y module measurements.