盐溶液中膨润土膨胀变形的计算方法

Method for calculating swelling deformation of bentonite in salt solution

膨润土的膨胀变形特性会受到盐溶液的渗透吸力的影响,其影响效果与在膨润土上施加外荷载产生的效果类似。因此,用与渗透吸力相关的修正有效应力来表示膨润土实际受到的总外应力。由分形理论可推导出:在双对数坐标下,修正有效应力与膨润土的最大膨胀变形间的关系可用一条直线表示;修正有效应力可利用溶液的渗透吸力和施加的外荷载求得。但不同浓度盐溶液的渗透吸力须通过较为复杂的试验获得,给工程实际应用造成了困难。基于修正的Debye-Hückel公式求得NaCl、NaNO3、CaCl2和Ca(NO3)2四种溶液在不同浓度下的渗透系数,结果经已有文献验证,计算方法可靠。以此为基础,进一步求得膨润土在不同浓度下所受到的修正有效应力。经试验数据验证,同种膨润土在不同浓度、不同种类溶液下的最大膨胀变形与修正有效应力之间在双对数坐标下存在统一的线性关系,符合理论公式。

A linear relationship between the maximum swelling deformation and the effective stress of bentonite under double logarithmic coordinates is derived based on the fractal theory. The effective stress of bentonite is related to the osmotic suction of concentration solution. However, the osmotic suction must be obtained through complicated tests, and it brings the difficulty to the practical application in projects. Based on the modified Debye-Huckel formula, the osmotic coefficients of CaCl2, NaCl, NaNO3 and Ca(NO3)2 solutions in different concentrations are obtained, and are proved to be reliable through other literatures. Then, the effective stress can be obtained by using the calculated osmotic suction. The maximum swelling deformations of the same kind of bentonite with different concentrations or different kinds of solutions have a unique linear relationship with the effective stress in log-log coordinates, which conforms to the theoretical formula.