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    Soil Parameters at Critical State for Ho Chi Minh Clay
    (2025-01-01)
    Nghia-Nguyen, Trong
    ;
    Uy-Vu, Nguyen Huu
    ;
    Chaiyaput, Salisa
    Ho Chi Minh City, a major economic hub in Southeast Asia, has witnessed significant growth, with numerous infrastructure projects demanding a thorough understanding of the underlying soil characteristics. However, unlike the extensively studied Bangkok clay, the critical state parameters of Ho Chi Minh clay have not been rigorously explored, despite its significance for geotechnical design. This study presents a novel investigation into the critical state behavior of Ho Chi Minh clay, focusing on its anisotropic properties, which sharply contrast with the isotropic behavior observed in Bangkok clay. Using an extensive series of triaxial tests in compression and extension, this research uncovers the unique stress–strain responses of Ho Chi Minh clay and its implications for construction in the region. The observed anisotropy in Ho Chi Minh clay is attributed to distinct microstructures related to the clay’s mineral composition and depositional history. The novelty of this study lies in its comparative approach, revealing significant differences between the geotechnical properties of Ho Chi Minh and Bangkok clays, and contributing valuable new insights to global geotechnical engineering. By establishing critical state parameters, this research fills a vital gap in understanding the geotechnical behavior of Ho Chi Minh clay, offering essential data for future infrastructure projects in the region.
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    Improving Groundwater Model in Regional Sedimentary Basin Using Hydraulic Gradients
    (2020-05-01)
    Tanachaichoksirikun, Pinit
    ;
    Seeboonruang, Uma
    ;
    Fogg, Graham E.
    Groundwater flow systems are strongly influenced by heterogeneity and anisotropy of hydraulic conductivity (K). Particularly in stratified clastic sedimentary aquifers, the vertical hydraulic gradient (dh/dz) is often very high, due to the low vertical hydraulic conductivity (K<inf>v</inf>) or high anisotropy (K<inf>h</inf>/K<inf>v</inf>). However, data on the vertical hydraulic gradient to calibrate the anisotropy is seldom available. We investigated the relationship between the variable K<inf>h</inf>/K<inf>v</inf> and the dh/dz computed by a groundwater flow model to improve the regional parameterization using an extensive data base on 3D distribution of hydraulic head. Although it is commonly assumed that the value of K<inf>h</inf>/K<inf>v</inf> is 10, our values typically ranged between 10 and 10<sup>5</sup>, because the maximum K<inf>h</inf>/K<inf>v</inf> was 10<sup>5</sup> in this regional basin. The simulations used MODFLOW-2000. We found that the high K<inf>h</inf>/K<inf>v</inf> contributed to high dh/dz, while identifying locations of potentially good vertical connectivity between the aquifer zones, where dh/dz is very low and difficult to measure sufficiently accurately. Sensitivity analysis of dh/dz to recharge and pumping from wells showed that recharge led to change in inflow of groundwater that led to head change, which in turn led to change in dh/dz. While, pumping contributed to aquifer outflow, as change in head drawdown around the influence zone, in turn changed dh/dz. Additionally, dh/dz in a shallower aquifer was more strongly affected by recharge and pumping.
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    In vitro measurement of myocardial impedivity anisotropy with a miniature rectangular tube
    (2003-04-01)
    Tsai, Jang Zern
    ;
    Will, James A.
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    Vorperian, Vicken R.
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    Hubbard-Van Stelle, Scott
    ;
    Cao, Hong
    Due to rapid change of fiber orientation, it is difficult to measure myocardial impedivity separately in a longitudinal or transverse fiber direction without mutual influence in the two directions. Previously published values of the longitudinal and the transverse myocardial impedivity were derived indirectly from measurements that mixed the impedivity in all directions. Those values are questionable because the derivations were based on a simplified uniform myocardial fiber model. In this paper, a miniature rectangular tube was devised to facilitate direct measurement of myocardial impedivity in a uniform fiber direction. The average transverse-to-longitudinal ratio of the measured in vitro swine myocardial impedivity was about 1.66 from 1 Hz to 1 kHz and dropped to 1.25 at 1 MHz. The result is important for accurate modeling of the electrical property of myocardium in biomedical research of radio-frequency cardiac catheter ablation.