盐溶液中膨润土膨胀变形的分形模型

Fractal model for swelling deformation of bentonite in salt solution

当压实膨润土在蒸馏水中膨胀后,施加于膨润土颗粒上的有效应力通常被认为是外部施加的荷载,而当膨润土在盐溶液中膨胀时,膨润土颗粒所承受的有效应力还包括由孔隙水渗透吸力所引起的渗透应力。而压缩膨润土的蒙脱石孔隙比e_m与膨润土颗粒承受的有效应力p之间满足分形关系,该关系可用来计算膨润土的膨胀变形。通过对压实膨润土在盐溶液中颗粒的分散情况以及颗粒表面的分形特性,推导出该渗透应力的表达式,进而得出膨润土颗粒所承受的有效应力。将所提出的有效应力代入分形模型中,计算GMZ01和MX-80膨润土在不同浓度NaCl溶液中的膨胀变形,将现有的两种膨润土膨胀试验结果与模型计算结果对比,发现具有较好的吻合度,在蒸馏水以及各浓度的盐溶液中膨润土的膨胀变形都可采用统一的e_m-p曲线表示,表明提出的有效应力符合膨润土颗粒在盐溶液中的实际受力情况。分形模型为研究膨润土在盐溶液中的膨胀性质提供了有效的计算方法。

When the compacted bentonite is inundated in distilled water, the effective stress on montmoriltonite particles is equal to the external load applied; in salt solution, the effective stress incorporates the osmotic stress due to the osmotic suction of pore water. In addition, .the relationship between void ratio em and the effective stress p of montmorillonite in compacted bentonite is found to satisfy a fi-actal relationship, which can be used to calculate the swelling deformation. Base on the dispersion and fractal characteristics of bentonite particles in salt solution, the expression of osmotic stress is derived, and the formula for effective stress on bentonite particles is developed. The swelling deformations of GMZ01 and MX-80 bentonites are calculated by incorporating the fractal model into the effective stress. Comparison of the experimental results available in the literature and the estimated value shows a good consistence. It is shown that the swelling deformation of bentonite can be expressed by a unified curve of em-p in distilled water or salt solution with different concentrations, implying that the proposed effective stress represents the actual force condition. The fractal model offers a good approach to expressing the swelling characteristics in salt solution.