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RISS 인기검색어
- 검색키워드
- 저자 : LianSheng Tang (검색결과 2 건)
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Process of pore pressure diffusion in saturated clay soil and impact of adsorbed water
LianSheng Tang,HaoKun Chen,Jing Song 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.5
Water molecules are adsorbed onto the surface and interlayer of clay minerals and form a film, which causes that pore pressure diffusion in clayey soils differs from that in granular material. In this paper, adsorbed water is classified into strongly adsorbed water and loosely adsorbed water, which provide a better understanding of the physical mechanisms of the adsorbed water. To investigate the impact of adsorbed water on pore pressure diffusion, a series laboratory tests were conducted, including the uplift pressure test, pore pressure diffusion test and adsorbed water content test. The experimental results implies that strongly adsorbed water can neither flow nor participate in pressure diffusion, but loosely adsorbed water shears at pressure gradients and participates in laminar flow. Therefore, as long as the dense clayey soil contains loosely adsorbed water, the pore pressure change at a local site can diffuse throughout the material. A concept called “loosely adsorbed water index (Ilo) is defined to characterize both the content and physical properties of loosely adsorbed water: (1) when Ilo ≥ 1, the peripheral water molecules of loosely adsorbed water layer essentially behave the same as free water; (2) as Ilo → 0, the physical properties of adsorbed water may evolve from a gel-like state to a solid-like state (strongly adsorbed water). According to the density of clay and the content of adsorbed water, the process of pore pressure diffusion can be divided into three modes: flow channels of free fluid, deformations of the adsorbed water layer and shear motions of the peripheral-adsorbed water molecules. Pore pressure response to additional water pressure strongly depends on the permeability, seepage path and boundary conditions. The time-lag effect of pore pressure diffusion should be considered in applications of effective stress in engineering.
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LianSheng Tang,Jing Song,HaoKun Chen,Ya Wang,JinLong Yin,JinLong Ye 한국지질과학협의회 2017 Geosciences Journal Vol.21 No.5
The vacuum preloading method combining prefabricated vertical drains (PVDs) and surcharge preloading from vacuum pressure is widely used in the improvement of dredger fill foundation. However, a clogging effect arises within the soils around the PVDs during the vacuum preloading, which significantly affects the soil consolidation. Previous studies indicated that the organic matter and soil pH circumstance influence the soil-water interaction and soil microstructure. In order to investigate the influences of organic matter and soil pH on the consolidation of clayey dredger fill, a series of small scale vacuum preloading tests was conducted on soils with different organic contents and soil pH values. Subsequently, Scanning Electron Microscopy observation test and vane shear test were carried out to evaluate the effect of vacuum preloading consolidation. The results showed that a low organic content or a high soil pH is beneficial for soil consolidation by vacuum preloading method, resulting in a more compact microstructure and a greater vane strength. There are two actions on the organic matter during the vacuum preloading consolidation, namely, material migration and organic matter dissolution. The organic matter dissolution effect is predominate at soil pH > 9.1, so that the consolidation effect is improved. However, the material migration effect is predominate at pH = 8.1, clay particles and organic matter can be transported with the water flow and redeposit near the drain pipes, resulting in a clogging effect. Moreover, a higher pH can induce the change of microstructure from flocculated association to deflocculated and dispersed association of clay particles, which is positive to soil consolidation. The results in this paper may offer helpful references for engineering practice.
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