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

Abstract

The shear strength of heavily overconsolidated, stiff-to-hard plastic clays is crucial to their stability and also influential on the ground movements they develop in many geotechnical engineering applications. This paper considers the shear strength anisotropy of the London, Gault, Kimmeridge and Oxford clays through advanced hollow cylinder experiments on multiple high-quality samples taken at similar depths from inland sites where the geotechnical profiles have been established by comprehensive laboratory and in situ testing. Suites of undrained tests are reported, which loaded specimens from their in situ stress states to reach ultimate failure at pre-defined final major principal stress axis orientations defined in the vertical plane, while also controlling or monitoring the intermediate principal stress ratio, b. Both stress path and simple shear tests were undertaken with the hollow cylinder apparatus, which offers key advantages over conventional simple shear equipment. The interpretation reveals patterns of marked shear strength anisotropy that impact significantly on numerous geotechnical engineering applications.

Anisotropic Stiffness and Shear Strength Characteristics of a Stiff Glacial Till

“…The evolving trends of t/sʹ (= q/(2pʹ)) against shear strain are plotted in Figure 18 Figure 19 show paths that all curve to the right after following initially contractant patterns. The Cowden till dilates strongly as it is sheared towards large strain critical state conditions, in contrast to the high OCR plastic marine clays tested by Brosse et al (2017) which bifurcated after relatively modest shear strains and started to develop residual shear structures after reaching their peak resistances.…”

“…The triaxial probing tests' initial conditions are summarised in (Symes, 1983). When b = 0.5, the stress variables (t, sʹ, q, pʹ) are linked simply to the Cauchy stress invariants, and the effective stress path inclinations d(σz-σθ)/d(2pʹ) do not vary with α; Brosse et al (2017). Two undrained triaxial compression (HCA TXC) tests were also performed.…”

“…Accurate knowledge of how anisotropy affects mechanical behaviour from any initial linear elastic response through to failure plays a key role in enabling representative numerical analyses of ground deformations and soil-structure interaction, see Hashash & Whittle (1996), Addenbrooke et al (1997), Zdravković et al (2001Zdravković et al ( , 2002, Jardine et al (2004) or Avgerinos et al (2016). Examples of improved characterisation of sedimentary clays has been achieved through advanced laboratory investigations of anisotropy include studies by Gasparre et al (2007), Nishimura et al (2007), Brosse et al (2016) and Brosse et al (2017) on four geologically aged highly over-consolidated stiff-to-hard UK clays; Nishimura (2014aNishimura ( , 2014b)'s research on six Japanese sedimentary clays and Ratananikom et al (2013)'s experiments on lightly over-consolidated Bangkok Clay. However, the key experimental evidence required to inform such analyses appear to be lacking for high yield stress ratio (YSR), stiff glacial tills, which are distributed widely over parts of the UK (Davies et al, 2011), northern Europe (Clarke et al, 2008) and North America (Fullerton et al, 2003), as well as parts of northern and central Asia, and under the Baltic, North, Norwegian and other Seas.…”

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

“…Note that the London clay was tested at higher effective stresses than the others because it was overlain at the rotary borehole location by 6m of Quaternary river terrace gravels which had been removed 70 years earlier at the block sampling area (Hight et al, 2007). The nearest group of triaxial tests reported by Gasparre et al (2007b) was from 12.6m below ground level at the rotary location (or 6.6m depth at the block area), while the HCA tests described by Brosse et al (2016) came from block samples taken at ≈10m depth. Hight et al (2007), Hosseini Kamal (2012) and Brosse (2012).…”

“…The geology and geotechnical characteristics of the Gault, Kimmeridge, and Oxford clay sampling locations' are summarised by Wilkinson (2011), Brosse (2012, Hosseini-Kamal (2012) and Hosseini-Kamal et al (2014). Brosse et al (2016) provide further details on how shear strength anisotropy was investigated in Hollow Cylinder (HCA) experiments.…”