Experimental quantification of 3D deformations in sensitive clay during stress-probing

Eleni Gerolymatou,Georgios Birmpilis,Olga Stamati,Edward Andò,Stephen A. Hall,Jelke Dijkstra

doi:10.1680/jgeot.21.00114

Abstract

Unique four-dimensional (4D) deformation data are collected during drained triaxial tests on intact specimens of a natural sensitive clay. This requires the development of a miniature triaxial cell for advanced stress path testing, specifically designed for X-ray computed tomography. Salient features include the omission of a membrane, and a mounting procedure that minimises disturbance by the experimenter. Three distinct drained stress ratios are studied for pseudo-isotropic, K0, and highly deviatoric loading paths. The results indicate that the K0 path shows the most uniform deformation mechanism, where the measured ratio of deviatoric and volumetric strain increments reach the stress ratio applied at boundary value level for large magnitudes of total strain. The pseudo-isotropic test also reaches a strain ratio close to η at large total strain levels; however, the deformation field is less uniform. Furthermore, the highly deviatoric stress path shows the most heterogeneous deformation fields commensurate with the applied stress ratio, although the ratio of deviatoric and volumetric strain increments falls above the η applied. The mean value of the three-dimensional spatial fields of strain corresponds well with the changes observed at boundary level, supporting prior research on drained stress-probing on clays for which there are no 4D deformation data available.

Highlights

Natural sensitive clays exhibit a complex non-linear response under coupled hydromechanical loading in, e.g., oedometric and triaxial tests (Burland, 1990; Smith et al, 1992; Karstunen and Koskinen, 2008)
The processed strain fields for the three tests are presented in Fig. 8 & Fig. 9 for the deviatoric strain and the volumetric strain, respectively
The results show that even though initially the principal strain axis deviates, locally in the specimen, from the principal stress axis, the strain and stress axes start to align at large magnitude of total strain

Summary

Introduction

Natural sensitive clays exhibit a complex non-linear response under coupled hydromechanical loading in, e.g., oedometric and triaxial tests (Burland, 1990; Smith et al, 1992; Karstunen and Koskinen, 2008). Since the seminal work of Delage and Lefebvre (1984), Electron Microscopy and MIP have greatly contributed to revealing the evolving microstructure of artificial and natural clays before and after mechanical perturbation (Lapierre et al, 1990; Tanaka and Locat, 1999; Mitaritonna et al, 2014; Cotecchia et al, 2019) Hattab and her co-workers (Hattab and Fleureau, 2010; Hattab et al, 2013) studied the evolution of the fabric orientation in relation to stress history for, respectively, reconstituted kaolin and reconstituted natural clays. This research aspires to improve the understanding between concurrent particle scale investigations and macroscale element testing, providing experimental evidence for the mesoscale, supporting further constitutive model development

Methods

Results

Conclusion