Appraisal of novel power-based extrusion methodology for consistency limits determinations of fine-grained soils

Abstract

The consistency limits (liquid limit LL and plastic limit PL) are among the most commonly performed tests in geotechnical engineering practice, being used for classification of fine-grained soils and in deducing other parameters (e.g., shear strength, permeability, compressibility), necessary for preliminary design/assessments, via numerous correlations built up over the decades. Depending on geographic region and/or referenced standard, the LL testing is performed using either the fall-cone or Casagrande (percussion-cup) approaches, while Atterberg’s PL is universally determined using the thread-rolling method. Because of its dependence on operator judgement regarding the crumbling condition during the rolling-out procedure, the accuracy of the PL test has been called into question by some researchers. This has prompted various alternative proposals, including undrained strength-based fall cone and extrusion approaches, but these are not appropriate for the determination of Atterberg’s PL which defines the water content at the plastic–brittle transition point (i.e., not strength-based). This paper presents the culmination of a two-year research project performed at Trinity College Dublin on the investigation and development of a novel power-based extrusion methodology for determination of the consistency limits of fine-grained soils.