高塌落度防渗墙填料扩散系数快速测定的透析试验

扩散是低渗透系数情况下溶质迁移的主要方式，目前尚没有测定高塌落度防渗墙填料扩散系数的试验方法。根据沥出试验原理，将处于流动状态的填料用半透膜包裹进行透析试验，通过有限圆柱中溶质迁移解析解对溶质迁移过程进行拟合求其扩散系数，探讨了试验和数据处理的相关问题，研究了膨润土含量和盐浴浓度对扩散系数的影响规律。结果表明，随拟合天数增加，填料中NaCl有效扩散系数减小，而误差增大；高塌落度填料中溶质迁移明显比压实土样中快，按拟合误差小于0.5%作为试验数据取舍依据，这一误差要求实际上是对溶质迁移以扩散为主导这一条件的量化，保证了采用纯扩散解析解进行数据拟合的合理性；扩散系数随填料中膨润土含量增加而减小，随盐浴浓度增加而减小，但在试验范围内数值变化不大，透析试验是快速测定防渗墙填料中溶质有效扩散系数的可行方法。

A dialysis test for fast measurement of diffusion coefficient of high slump backfill

Diffusion is the dominant solute transport process in high slump backfill with low hydraulic conductivity. However, the method to measure the diffusion coefficient is not available. Based on the theory of dynamic leaching test, a dialysis test method was adapted to measure the diffusion coefficient of NaCl diffusing from flowing-state backfills with different bentonite contents at different initial NaCl concentrations. The solution for solute transport in a finite cylindrical medium was used to calculate the diffusion coefficient. Test procedure and problems in data analysis were discussed. The results show that, as more data are used, the effective diffusion coefficient of NaCl decreases and the relative regressing error increases. Diffusion in backfill is obviously faster than that in compacted specimen. The total data sets are truncated until a relative error of less than 0.5% is achieved. This relative error quantitatively describes the dominant role of diffusion in solute transport process, and assures the validity of the data fitting using the pure-diffusion analytical solution. The measured diffusion coefficient decreases as the bentonite contents and initial NaCl concentrations increase. However, variations of the values are roughly small in the test range. The dialysis test is a feasible method for quick measurement of solute diffusion coefficient in cutoff wall backfill.