Investigation of fabric evolution using bidirectional shear wave velocity measurements

Abstract

In order to characterise fabric evolution, continuous bidirectional shear wave velocity measurements are performed in vertical and horizontal directions (V&H) on triaxial soil specimens during shearing in which two horizontal piezo-electrics were mounted on samples using a new measurement technique. The specimens are prepared by wet tamping method and then subjected to strain-controlled compressional shearing under drained and undrained conditions. The shear wave velocities of all drained specimens initially increased as the loading commenced and then converged to a unique state in both horizontal and vertical directions. The shear wave velocity of undrained specimens on the other hand, for both horizontal and vertical directions initially decreased due to the rising of the excess pore water pressure and then gradually approached a unique shear wave velocity like drained specimens. The fabric condition or stiffness in V&H directions of all the examined drained and undrained specimens at critical state are found to be unique.

Influences of initial anisotropy and principal stress rotation on the undrained monotonic behavior of a loose silica sand

“…Different studies have also demonstrated that soil behaves anisotropically even in the small-strain domain (Shirley and Hampton 1978;Bellotti et al 1996;Pennington et al 1997;Hoque et al 1998;Ng et al 2004;Ezaoui et al 2009;Gu et al 2015;Fakharian et al 2019). Moreover, there are some shreds of evidence D r a f t suggesting that the fabric becomes greatly anisotropic at the critical state (Nakakuki and Oda 1972;Masson and Martinez 2001;Li and Yu 2009;Yan and Zhang 2012).…”

“…The first major peak method was used to determine the travel time. For more details on the employed method, signal interpretation, horizontal bender element mounting, etc., please refer to Fakharian et al (2019) and Kaviani-Hamedani et al (2021).…”

Influence of Initial Anisotropy, Stress Path and Principal Stress Rotation on Monotonic Behavior of Clean and Mixed Sands

“…The specimens were prepared using either "moist tamping" (MT) or "water sedimentation" (WS) methods. For specimens that were accompanied by bidirectional bender elements, the on-sample horizontal bender housings for MT and WS specimens during sample preparation are located in a parking spot "bender capsule" and out of parking spot "pre-penetrated in soil", respectively (for more details, refer to [14], [17].…”

“…Classical critical state theory assumes that the soil fabric at the critical state becomes isotropic [16]. Nonetheless, soil behaves anisotropically during shearing on account of the microscopic characteristics of soils [17], [18]. This anisotropic behavior is also understood to influence the soil behavior in small-strain domain [11], [17], [19]- [21].…”

“…Nonetheless, soil behaves anisotropically during shearing on account of the microscopic characteristics of soils [17], [18]. This anisotropic behavior is also understood to influence the soil behavior in small-strain domain [11], [17], [19]- [21]. Moreover, there are some shreds of evidence suggesting that the fabric becomes greatly anisotropic at the critical state [22], [23].…”