Failure Modes of Sand in Undrained Cyclic Loading: Impact of Sample Preparation

Abstract

This paper presents a systematic experimental investigation into the impact of specimen preparation on the cyclic loading behavior of saturated sand, including the deformation pattern, pore-water pressure generation, stress-strain relationship, and cyclic shear strength. Moist tamping and dry deposition were used in the laboratory to prepare sand specimens with distinct fabrics for cyclic triaxial tests under a range of conditions. It is found that the soil fabric formed by dry deposition can lead to unique failure modes different from those of moist-tamped samples in certain situations. These failure modes are hybrid in nature, characterized by a contractive response in the form of limited flow followed by cyclic strain hardening in the form of either cyclic mobility or plastic-strain accumulation. The hybrid nature of the failure patterns makes defining failure for liquefaction-resistance evaluation crucial; the conventional failure criteria based on a certain level of strain or pore-water pressure do not appear to properly represent the failure mechanism involved and may lead to a substantial overestimation of liquefaction resistance. The experiments reveal that the method used to reconstitute specimens or the soil fabric they form plays a role that is far more complicated than previously thought. Depending on the combination of relative density, confining stress, and degree of stress reversal in cyclic loading, a change of reconstitution method can have a marked or little effect on the nature of the response in terms of deformation pattern and failure mechanism; nevertheless, the two reconstitution methods always give significantly different liquefaction-resistance values under otherwise similar testing conditions.

Constitutive Modeling of Anisotropic Sand Behavior in Monotonic and Cyclic Loading

“…This is mainly because sand samples that are more anisotropic show more contractive responses in the triaxial extension side in cyclic loading. For the same anisotropic sand deposit tested with horizontal and vertical deposition plane orientations, the sample with the horizontal deposition plane has higher undrained shear strength in monotonic triaxial compression tests but lower liquefaction resistance in undrained cyclic triaxial tests, which is also owes to the fact that it shows more contractive response in the triaxial extension side during cyclic loading (Miura and Toki 1984;Oda et al 2001;Sze and Yang 2014).…”

“…The function h m is proposed based on the observations of monotonic sand behavior wherein the shear modulus increases as the void ratio decreases and the anisotropic variableĀ increases (Li and Dafalias 2012). The term ð1 þ FÞ 2 is used to render h 1 to decrease with F. This is based on experimental observations that more anisotropic sand samples show a higher rate of positive excess pore pressure accumulation in undrained cyclic loading under otherwise identical conditions (Miura and Toki 1982;Sze and Yang 2014).…”

“…Meanwhile, the undrained shear strength and cyclic liquefaction resistance of sand, which are of great concern in earthquake engineering design, are also found to be strongly dependent on the degree of fabric anisotropy and the relative orientation between the loading direction and material fabric Toki 1982, 1984;Yoshimine et al 1998;Uthayakumar and Vaid 1998;Oda et al 2001;Sze and Yang 2014). For instance, Miura and Toki (1982) and Sze and Yang (2014) found that sand deposits with a higher degree of anisotropy (bedding plane is horizontal) show higher undrained shear strength in monotonic triaxial compression tests but lower liquefaction resistance in undrained cyclic triaxial tests. This is mainly because sand samples that are more anisotropic show more contractive responses in the triaxial extension side in cyclic loading.…”

A multiscale approach for investigating the effect of microstructural instability on global failure in granular materials

“…Failure modes of granular materials and their different mechanisms have been widely studied. 14,22,29,61 Generally, two specific failure modes, localised and diffuse failures, have been observed. 34,39,42 In localised failure, the strain is concentrated in shear bands; the displacement field is highly heterogeneous and organised.…”

Mohr–Coulomb plasticity for sands incorporating density effects without parameter calibration

“…Nevertheless, one must aware the limitations of the empirical equations. For example, the equations do not consider some important properties that can greatly affect the strength and dilatancy of sands, such as fabric and particle shapes (see, eg, other works for the significance of these properties). Also importantly, the equations have been derived from experimental data under axisymmetric and plane strain conditions, so their validity becomes increasingly questionable as the stress/strain condition deviates more from these two conditions.…”