Impact of Effective Stress on the Dynamic Shear Modulus of Unsaturated Sand

Abstract

The dynamic shear modulus of soils is needed to predict soil behavior in response to cyclic loading. Even though the effective stress has been shown to have a significant impact on the dynamic modulus of water-saturated and dry soils, its effect on the dynamic shear modulus of unsaturated soils has not been evaluated. Specifically, studies on the dynamic response of unsaturated soils have characterized variations in small-strain shear modulus (G max) as a function of the degree of saturation or matric suction alone. In contrast, this study evaluates the use of the suction stress characteristic curve to characterize the impact of mean effective stress (' m) on the dynamic shear modulus of unsaturated sand. A fixed-free resonant column test device was adapted with a hanging column setup so that the small-strain dynamic shear modulus could be measured for sand specimens under different confining pressures and matric suction values. Trends between the small strain shear modulus and effective stress for unsaturated sand were found to be different from those reported in the literature, where G max varied linearly with the square root of ' m .

Stiffness of intermediate unsaturated soil from simultaneous suction-controlled resonant column and bender element testing

“…Matric suction was induced via axis-translation, while the torsional torque was steadily increased to study soil stiffness at small-, mid-, and high-shear strain amplitudes. Results within the small-strain range were similar to those reported by Cabarkapa et al (1998) using bender elements, and by Khosravi et al (2010) using resonant column.…”

“…Over the last two decades, several power law relationships have been empirically or semi-empirically developed for shear-wave velocity or shear modulus of unsaturated soils for different choices of stress state variables, including the critical role of void ratio, K o , OCR, degree of saturation, volumetric water content, matric suction and, more recently, the role of hardening and hydraulic hysteresis (Cho and Santamarina, 2001;Mancuso et al, 2002;Mendoza et al, 2005;Sawangsuriya et al, 2008;Ng and Yung, 2008;Khosravi et al, 2010;Hoyos et al, 2011;Khosravi and McCartney, 2012;Heitor et al, 2013). As enlightening as these previous efforts have proved to be, virtually no attempt has ever been made to develop a unified framework for unsaturated soil stiffness that also embraces material damping as a fundamental property, particularly in intermediate geomaterials: Fig.…”

Hydro-mechanical behavior of undisturbed collapsible loessial soils under different stress state conditions

“…Accordingly, it would be expected that the trend between the steady state deviator stress values and mean effective stress of saturated soils is consistent with that for unsaturated soils when using the effective stress approach (Eq. (2)) (Khalili et al, 2004;Khosravi and McCartney, 2009). In Fig.…”

Cyclic Triaxial Test to Measure Strain-Dependent Shear Modulus of Unsaturated Sand

“…where G = strain-dependent shear modulus; g = shear strain; and g r = reference shear strain corresponding to G/G 0 = 0.5. Recent advancements in unsaturated soil mechanics have revealed the clear influence of the degree of water saturation on the dynamic properties of soils (Khosravi et al 2010(Khosravi et al , 2016. This is a result of the presence of interparticle suction forces that change the effective stresses in soils (Khalili et al 2004) and, in turn, the mechanical response.…”

“…Experimental difficulties, such as direct measurement and control of matric suction, have hindered the investigation of the dynamic behavior of unsaturated soils. Although researchers have increasingly explored the effect of degree of saturation on the dynamic soil modulus and damping, they have mostly focused on the small-strain shear modulus for various suction values or degrees of saturation using bender element or resonant column tests (Wu et al 1984;Qian et al 1991;Marinho et al 1995;Cho and Santamarina 2001;Mancuso et al 2002;Mendoza et al 2005;Alramahi et al 2008;Ng et al 2009;Khosravi et al 2010;Hoyos et al 2015). In addition, in some recent studies, researchers investigated the effect of suction on the strain-dependent shear modulus, soil volume change, stress path, pore pressure, and drainage conditions in cyclic triaxial systems (Cui et al 2007;Craciun and Lo 2010;Biglari et al 2011;Kimoto et al 2011;Cary and Zapata 2016).…”