Pore water pressure responses of saturated sand and clay under undrained cyclic shearing

Abstract

In this study, changes in the pore water pressure were observed for saturated specimens of a loose fined-grain sand (Nam O sand) and a soft silty clay (Hue clay) subjected to undrained cyclic shearing with different testing conditions. The cyclic shear tests were run for relatively wide range of shear strain amplitude (g = 0.05%-2%), different cycle numbers (n = 10, 50, 150 and 200) and various shear directions (uni-direction and two-direction with phase difference of q = 0o, 45o and 90o). It is indicated from the experimental results that under the same cyclic shearing condition, the pore water pressure accumulation in Hue clay is at a slower rate, suggesting a higher cyclic shear resistance of Hue clay than that of Nam O sand. Liquefaction is reached easily in nominally 50% relative density specimens of Nam O sand when g ³ 0.4%, meanwhile soft specimen of Hue clay is not liquefied regardless of the cyclic shearing conditions used in this study. The threshold number of cycles for the pore water pressure generation generally decreases with g meanwhile, the threshold cumulative shear strain for such a property mostly approaches 0.1%. In addition, by using this new strain path parameter, it becomes more advantageous when evaluating the pore water pressure accumulation in Nam O sand and Hue clay subjected to undrained uni-directional and two-directional cyclic shears.

Effects of physical properties and undrained cyclic shear conditions on the pore water pressure responses of saturated sands and clays

“…This parameter was referred to as the threshold number of cycles for cyclic shear-induced pore water pressure generation, symbolized as n tp . n tp was generally mentioned for clays and sands (Nhan et al, 2012;Nhan, 2013;Nhan and Matsuda, 2020) and recently determined in more detail for Hue clay and Nam O sand subjected to uni-directional and twodirectional cyclic shears (An et al, 2022). Therefore, in this study, n tp should be determined for Toyoura sand and Kaolin subjected to the same cyclic shearing conditions so that the effects of the soil properties and cyclic shearing conditions can be considered.…”

“…Besides widely spreading along the coastal plain in Thua Thien Hue and Quang Tri provinces, the soils also have changeable thickness and distribution depth and, in most case, extends close to the ground surface (Nhan, 2004;Thao, 2004;Vy, 2007). The map typically showing the distributions of Nam O sand and Hue clay has been presented by An et al (2022).…”

“…Therefore, the dynamic properties of such soils have been observed in previous research in which information about the soils can be referred to in more detail (Nhan, 2019;Nhan and Matsuda, 2020;An et al, 2022;. Kaolin clay, a standardized clay, and Toyoura sand, a natural sand, are commonly used for laboratory testing in Japan (Lashkari, 2009;Matsuda et al, 2011;.…”

“…In Table 3 and Fig. 10, the results of n tp on Nam O sand and Hue clay (symbolized as n and n tpHU , were referred from previous research (An et al, 2022) which method for determination of n tp was described in detailed. The observations indicate that n tp generally decreases with  regardless of the types of soils and the cyclic shear direction.…”

“…Based on several series of uni-directional and two-directional cyclic shear tests on normally and over-consolidated clays (NC and OC clays), Matsuda et al (2015) indicated that  tp induced by the twodirectional cyclic shear increases from 0.1% to 0.2% for the range of OCR from 2 to 5 and is smaller than those induced by the unidirectional cyclic shear which had been confirmed to increase from 0.05% to 0.29% for OCR from 1 to 6 by Matsuda and Ohara (1989). In addition, since the relative density and the Attergerg's limits have been confirmed in significantly affect the dynamic behavior of soils subjected to different cyclic shear conditions and models (Matsuda et al, 2011;Vucetic and Dobry, 1991), the threshold number of cycles and cumulative shear strain for pore water pressure generation and buildup have been generally compared between different soils (Nhan et al, 2012;Nhan and Matsuda, 2020) and initially clarified in more detail for Nam O sand and Hue clay (An et al, 2022). Therefore, in this study, the pore water pressure properties, including such parameters for pore water pressure generation in these soils, were further observed and compared with those obtained…”