Penetration Resistance and Stiffness Factors for Hemispherical and Toroidal Penetrometers in Uniform Clay

Abstract

This paper reports numerical analyses of shallowly embedded hemispherical and toroidal penetrometers under torsional and vertical load. These novel penetrometers are a new design suited to the assessment of near-surface soil strength and are aimed at the analysis of pipeline embedment and axial pipe-soil interaction. The geometry of the penetrometers avoids the complication of end effects that arise if a short pipe segment is used, as is the current practice. The operation of these devices involves vertical penetration typically of up to half a diameter, followed by rotation about the vertical axis, whereas the corresponding loads are recorded. The FE analyses explore the undrained bearing capacity and stiffness factors required for the measured loads to be converted to soil strength and stiffness for application in design. On the basis of these analyses, the geometry of the toroidal penetrometer has been optimized to minimize the size of the instrument and limiting interference across the toroid, which would hamper comparisons between the penetrometer response and a pipeline. It is shown that a relatively compact toroid can be used.