Exposure of bentonite to salt solution: Osmotic and mechanical effects
Exposure of bentonite to salt solution: Osmotic and mechanical effects
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DOI：
10.1680/geot.1996.46.4.695
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发表时间：
1996-12-01
期刊：
影响因子：
5.8
通讯作者：
DiMaio, C
中科院分区：
文献类型：
--
作者：
DiMaio, C
粘土的力学行为受孔隙流体组成的强烈影响。此外，暴露于与其孔隙流体不同的流体可能产生瞬态阶段，在此期间粘土经历明显的体积变化。本文的目的是探讨这些现象及其原因。为此，大量的水饱和的Ponza膨润土试样（主要由Namontitrium组成），交替地暴露于蒸馏水和饱和NaCl，KCl或CaCl 2溶液中的过程中，在实验室直接剪切试验和oedometer tests.Exposure到任何三种电解质产生的试样的固结，变形能力大幅度下降和同样大的残余剪切强度增加。在平衡状态下，力学行为变得非常类似于直接用适当的盐溶液作为孔隙流体制备的试样所表现出的力学行为。对于这两种类型的标本（即那些准备与电解质和那些暴露于它）NaCl的影响是可逆的，当标本重新暴露于水，而KCl和CaCl2的影响持续甚至经过几个月的连续testing.The实验结果是一致的假设，即扩散双层的厚度的变化所产生的离子扩散进入或离开粘土。X射线衍射分析表明，在KCl和CaCl 2的情况下，向内扩散产生了离子交换。因此，在给定的实验条件下，扩散双层的减少是永久性的，并且它使得随后的渗透现象几乎可以忽略不计。
The mechanical behaviour of clays is strongly influenced by pore fluid composition. Moreover, exposure to fluids different from their pore fluid may produce a transient stage during which the clays undergo noticeable volume changes. The aim of this paper is to investigate these phenomena and their causes. To this end, a large number of water-saturated specimens of Ponza bentonite (mainly composed of Namontmorillonite) were exposed, alternately, to distilled water and to saturated NaCl, KCl or CaCl2 solutions in the course of laboratory direct shear tests and oedometer tests.Exposure to any of the three electrolytes produced consolidation of the specimens, a large decrease in deformability and an equally large increase in residual shear strength. At equilibrium, the mechanical behaviour became very similar to that exhibited by specimens that had been directly prepared with the appropriate salt solution as pore fluid. For both types of specimen (i.e. those prepared with the electrolyte and those exposed to it) NaCl effects were reversible when the specimens were re-exposed to water, while KCl and CaCl2 effects persisted even after some months of continuous testing.The experimental results were consistent with the hypothesis that changes in the thickness of the diffuse double layer were produced by ions diffusing into or out of the clay. X-ray diffraction analysis showed that, in the cases of KCl and CaCl2, the inward diffusion had produced ion exchange. Hence, the decrease of the diffuse double layer was permanent, under the given experimental conditions, and it rendered subsequent osmotic phenomena practically negligible.