Strength Characteristics of Highly Organic Soil Obtained by Direct Shear Tests

Experimental determination of the shear strength of peat from standard undrained triaxial tests: correcting for the effects of end restraint

“…Direct shear and ring shear tests are sometimes adopted, although stress non-uniformity, which is amplified by the presence of fibres and by the large strains attained by peat samples, makes the results rather arguable (e.g. Landva & La Rochelle, 1983;Stark & Vettel, 1992;Farrell & Hebib, 1998;Ogino et al, 2002;Komatsu et al, 2011). In the recent practice, direct simple shear is widely preferred, assuming that more uniform stress and strain states are guaranteed compared to the direct and ring shear, that the effects of fibres stretch are prevented and, especially, that the test better replicates the deformation mode characterising failure in the field (Farrell et al, 1999;Boylan & Long, 2008;Zwanenburg et al, 2012;Den Haan & Grognet, 2014;O'Kelly, 2017).…”

“…Oikawa & Miyakawa (1980) suggested to identify failure as the transition between contractive and dilatant response. Alternatively, adopting strain based approaches, the mobilised shear strength at convenient axial strain thresholds has been used to define operational shear strength parameters (15% in Ogino et al (2002) and Hayashi et al (2012), 2% and5% in Den Haan &Feddema (2013) from undrained compression tests, and 20% in Zhang & O'Kelly (2014) from drained compression tests). Despite these approaches being useful in the practice, they reveal absence of consistency in the strength evaluation of peats from triaxial tests.…”