Reverse extrusion test for fine-grained soil characterisation: internal flow pattern with ANN-enhanced particle tracking

Abstract

The reverse extrusion test involves one-dimensionally (1D) compressing a fine-grained soil sample contained in a cup container of cross-sectional area A. The force Fe applied by the loading platen causes extrusion of the soil to occur via a small and centrally located orifice on the platen. The applied force is continuously monitored during the test, with the pressure value causing extrusion (i.e., 𝑝e = 𝐹e 𝐴⁄ ) proposed as a means of quantifying the undrained shear strength and consistency limits of fine-grained soils [1]. Previous experimental results showed that the pe value correlates well with undrained shear strength at various water content for a specific soil type [2]. However, their relationship varies between soils and also depends on the compression velocity. Gas bubbles entrained during sample preparation and the complex internal flow pattern and possible localized sample consolidation that occur during the extrusion test [2] hinder understanding of the mechanism of the extrusion test. Thus, we adopted X-ray computed tomography (CT) combined with a recently developed marker-based tracking algorithm [3,4] to quantify the internal flow pattern of saturated kaolinite during extrusion tests.