Stress–strain pattern–based criterion to assess cyclic shear resistance of soil from laboratory element tests

Abstract

The cyclic shear response of soils is commonly examined using undrained (or constant-volume) laboratory element tests conducted using triaxial and direct simple shear (DSS) devices. The cyclic resistance ratio (CRR) from these tests is expressed in terms of the number of cycles of loading to reach unacceptable performance that is defined in terms of the attainment of a certain excess pore-water pressure and (or) strain level. While strain accumulation is generally commensurate with excess pore-water pressure, the definition of unacceptable performance in laboratory tests based purely on cyclic strain criteria is not robust. The shear stiffness is a more fundamental parameter in describing engineering performance than the excess pore-water pressure alone or shear strain alone; so far, no criterion has considered shear stiffness to determine CRR. Data from cyclic DSS tests indicate consistent differences inherent in the patterns between the stress–strain loops at initial and later stages of cyclic loading; instead of relatively “smooth” stress–strain loops in the initial parts of loading, nonsmooth changes in incremental stiffness showing “kinks” are notable in the stress–strain loops at large strains. The point of pattern change in a stress–strain loop provides a meaningful basis to determine the CRR (based on unacceptable performance) in cyclic shear tests.

Mechanisms of shear strain accumulation in laboratory experiments on sands exhibiting cyclic mobility behavior

“…Other factors such as the grain properties (Kokusho et al 2004), static shear bias (Sivathayalan and Ha 2011;Chiaro et al 2012), testing device (Bhatia et al 1985) or the initial soil fabric as determined by the sample preparation method (Vaid and Sivathayalan 2000;Sze and Yang 2014) have also been found to play a role in experimentally obtained sand responses. The effect of these factors is typically captured through frameworks that allow for the quantification of key aspects of the soil response like the pore pressure generation (e.g., Seed et al 1976) and liquefaction triggering resistance (e.g., Seed and Lee 1966;Wijewickreme and Soysa 2016). However, few frameworks are available in the literature for quantitative evaluations of the post-triggering response and the accumulation of shear strains of sands undergoing cyclic mobility.…”

Stiffness– and damping–strain curves of sensitive Champlain clays through experimental and analytical approaches

“…On the other hand, the resonant column (RC) is used to characterize the dynamic properties of soils from low to intermediate strain region, γ=0.0001% to 0.05% (e.g., Hardin 1970;Hardin and Drnevich 1972;Drnevich et al 1978;Tatsuoka et al 1978, Goudarzy et al 2017) and therefore the stiffness degradation and damping versus strain (G/G 0 -γ and ξ% -γ, where G 0 is the maximum shear stiffness of soils) curves are obtained from RC experiment up to intermediate strain level. The other laboratory methods, direct simple shear (DSS) (e.g., Roscoe 1953;Bjerrum and Landva 1966;Boulanger et al 1993;Lanzo et al 1997;Wijewickreme and Soysa 2016), cyclic triaxial (CTX) (e.g., Peacock and Seed 1968;Kokusho 1980;Simcock et al 1983;Gu et al 2017), and cyclic torsional shear (e.g., Iwasaki et al 1978;Bhatia et al 1985) apparatuses are applicable to characterize D r a f t dynamic properties of soils for wider strain range, up to large strain level. In fact, RC and BE methods of measuring shear wave velocity, s V and consequently G 0…”