Undrained stiffness anisotropy from hollow cylinder experiments on four Eocene-to-Jurassic UK stiff clays

Abstract

The paper describes the anisotropic undrained stiffness behaviour of four medium-plasticity heavily overconsolidated UK stiff marine clays as revealed through hollow cylinder testing. The experiments contributed to two broader studies on stiff-to-hard London, Gault, Kimmeridge, and Oxford clay strata. They involved static and dynamic testing of multiple high-quality natural specimens sampled at similar depths from inland sites. This paper explores the directional dependency of the clays’ highly nonlinear undrained stiffness characteristics. New data-analysis approaches are outlined that allow the stiffnesses associated with one-dimensional vertical, horizontal, or pure horizontal shear modes to be isolated in complex undrained stress paths. In the presented experiments, loading progressed from in situ stresses to reach ultimate failure at a range of final major principal stress orientation angles α (defined in the vertical plane) while keeping fixed values of the intermediate principal stress ratio, b. The tests reveal strong undrained stiffness anisotropy that can impact significantly on the prediction and understanding of ground deformation patterns in numerous geotechnical engineering applications.

The undrained shear strength anisotropy of four Jurassic to Eocene stiff clays

“…Drained isotropic reconsolidation was conducted first to reach the desired p′ values and then (σ z À σ θ )/2 was reduced, keeping constant p′, to reach the estimated in situ effective stress conditions. Small-strain non-destructive resonant column tests were conducted during all ICRCHCA tests to monitor how G zθ varied during reconsolidation and shearing; see Gasparre et al (2007b) and Brosse et al (2016Brosse et al ( , 2017. The latter had no discernible effect on permanent strains or pore water pressures and so did not affect the subsequent strength measurements.…”

“…Nishimura (2006), Nishimura et al (2007Nishimura et al ( , 2008 and Brosse (2012) provide numerous two-dimensional (2D) and three-dimensional (3D) plots to describe the effective stress paths and stress-strain relationships provided by the four degree of stress and strain freedom HCA experiments. This paper focuses on the sub-set of outcomes that are essential to characterise undrained shear strength anisotropy, while Brosse et al (2016) describe the anisotropic and highly non-linear stiffness characteristics revealed by the HCA tests.…”

“…The second comprised simple shear HCA tests on samples tested from in situ and other effective stress conditions. Nishimura (2006), Nishimura et al (2007Nishimura et al ( , 2008 and Brosse (2012) provide further details of the experiments and interpretation, while Brosse et al (2016Brosse et al ( , 2017 report on the four clays' highly non-linear, pressure-dependent and anisotropic pre-failure stiffness characteristics.…”

Assessment of liquefaction characteristics of sand under coupled action of compression and shear waves

“…In a dynamic loading environment such as earthquake, wave or traffic loading, these rotations are continuous and cyclic in nature. Several studies have shown that the shear strength characteristics of soils are heavily influenced by the mode of load application (Uthayakumar and Vaid 1998;Foundoukos 2006;Minh 2006;Brosse 2012;Lade et al 2013). The effect of loading mode on the drained and undrained shear behaviour of soil will be discussed in detail in the forthcoming sections.…”

“…The stress path dependent behaviour of natural soil deposit due to its crossanisotropic fabric has been relatively well established. Several systematic studies conducted using a hollow cylinder torsional shear (HCT) device (Symes et al 1984;Miura et al 1986;Uthayakumar and Vaid 1998;Sivathayalan and Vaid 2002;Nishimura et al 2007;Lade et al 2013;Brosse et al 2017;Georgiannou et al 2018) revealed that orientation of major principal stress during shear has a considerable influence on the anisotropic strength and stiffness characteristics of soil. It has been observed that during monotonic shearing with a fixed principal stress direction, soil showed a weak softening response when the direction of major principal stress aligns along the weak bedding plane.…”