Characterizing the variation of small strain shear modulus for silt and sand during hydraulic hysteresis

Abstract

Abstract. Experimental studies have indicated that the small strain shear modulus, Gmax, of unsaturated silt and clay has a greater amount during imbibition than during drainage, when presented as a function of matric suction. However, due to material properties and inter-particle forces, different behavior is expected in the case of sand. Although considerable research has been devoted in recent years to characterize the behaviour of Gmax of sand during drainage, rather less attention has been paid to the effect of hydraulic hysteresis on Gmax and its variations during imbibition. In the study presented herein, an effort has been made to compare the Gmax behavior of specimens of silt and sand during hydraulic hysteresis. In this regard, a series of bender element tests were carried out in a modified triaxial test device with suction-saturation control to evaluate the impact of hydraulic hysteresis on Gmax for specimens of silt and sand. Trends between the Gmax and matric suction for unsaturated sand were found to be different from those for silty specimens. The variations in Gmax showed an up and down trend in both drainage and imbibition paths for sandy specimens, where plotted as a function of matric suction. Results also indicated smaller magnitudes of Gmax upon imbibition than those during drainage; a behavior which is believed to be attributed to variations in suction stress with matric suction. In silty specimens, a stiffer response was measured during imbibition which was hypothesized to be due to drainage-induced hardening experienced by the specimens that was not fully recovered during imbibition.

Cyclic Direct Simple Shear Test to Measure Strain-Dependent Dynamic Properties of Unsaturated Sand

“…However, the shear modulus relation might be different depending on the effective stress formula, strain level, and also testing method. For example, Ghayoomi et al (2017) used triaxial test, or Khosravi et al (2016) used resonant column test to show that still there would be meaningful increase in normalized modulus (or constant effective stress modulus) by increasing the suction or change of the degree of saturation. Considering the suction dependency of the shear modulus, in addition to the previously known affecting parameters, such as the effective stress, the void ratio, OCR, and the shear strain, an additional term could be included in…”

Wave Propagation and Elasticity in Granular Soils: A Numerical Approach for a Micromechanical Perspective

“…Since the degree of saturation along a drying path is higher than the degree of saturation along a wetting path, one would expect G to be higher along a drying path. Although an evidence of this has been observed experimentally [23], a number of experimental investigations show an opposite trend, i.e., the soil is observed to be significantly stiffer along a wetting path [24,40]. Inspection of experimental data also reveals that the change of G with suction or degree of saturation occurs in either a monotonic or non-monotonic fashion [23,45].…”

“…Although an evidence of this has been observed experimentally [23], a number of experimental investigations show an opposite trend, i.e., the soil is observed to be significantly stiffer along a wetting path [24,40]. Inspection of experimental data also reveals that the change of G with suction or degree of saturation occurs in either a monotonic or non-monotonic fashion [23,45]. Ideally, a stiffness model should be capable of capturing the physics behind the two observed behaviours.…”