Large strain shearing behaviour of untreated and polymer treated clayey silt slurry specimens

Abstract

Polymer treatment (PT) of tailings has been observed experimentally and in physical models, resulting, in some cases, in changes to geotechnical properties including: (i) higher hydraulic conductivity, (ii) lower density at a particular vertical effective stress, (iii) a change to the critical state line (CSL), and (iv) different penetrometer response when at the same in situ state. The different CSLs observed could be theorised to converge at sufficiently high strain once the PT fabric had broken down through shearing. However, the available penetrometer test results in controlled centrifuge experiments do not support the suggestion of converging CSLs, with drastically different cone penetration test (CPT) resistance seen in PT clayey silt of importance as the CPT represents a large strain measure. To further investigate PT effects on shearing, a series of multi-stage direct simple shear and constant volume ring shear tests was carried out to investigate the large strain response of untreated (UT) and PT specimens. The tests showed consistently higher, or similar, large strain strengths from PT specimens despite their lower consolidated densities. This result is generally consistent with previous observations of an increase to CSL elevation from PT.