盐溶液环境下钙质砂渗透性影响因素分析

Analysis of factors affecting permeability of calcareous sand in salt solution environment

渗透性是指溶液在砂土体孔隙中渗透流动的性能,渗透系数K作为衡量土体渗透性的重要指标,其大小受多种因素综合影响,目前有关砂土体渗透特性的研究基本在淡水环境下开展,而钙质砂属于海相沉积砂,处于具有一定盐浓度的海水环境中。为探究盐溶液环境下,孔隙比、颗粒粒径及溶液盐含量对钙质砂渗透性的影响,基于KAST土壤饱和水力导度测量仪开展常水头和变水头渗透试验,并通过Zeta电位和接触角试验进行微观探讨。研究结果表明:钙质砂均值粒径对渗透系数影响最大,均值粒径变化将导致渗透系数产生数量级上的差异;渗透系数K与渗透液含盐量P呈负相关关系,与孔隙率n和均值粒径da呈正相关关系。通过这些影响因素分析,建立了考虑渗透液含盐量因素在内的渗透系数计算模型,该模型可为中国南海人工吹填岛礁渗透性评估、地下淡水演化分析提供参考。

Permeability is the capacity of a soil for transmitting a fluid,e.g.,a salt solution,through soil pores.The permeability coefficient K is an important measurement of the soil permeability,which is affected by various factors.The existing research on the permeability of sandy soil is basically carried out in the freshwater environment.However,the calcareous sand is a typical marine sedimentary sand,which is deposited in the seawater environment with certain salt concentrations.In order to investigate the influence of void ratio,particle size and concentration of the salt solution on the permeability of calcareous sand in a salt solution environment,constant head and falling head permeability tests were carried out using the meter KAST-soil saturated hydraulic conductivity.The microscopic characteristics were investigated through Zeta potential and contact angle tests.The results showed that the mean particle size has the greatest influence on the permeability coefficient of a calcareous sand,and the change of the mean particle size will even lead to the difference in the order of magnitude of the permeability coefficient.The permeability coefficient(K)is negatively correlated with the salinity of the transmitting solution(P),and positively correlated with the porosity(n)and the mean particle size(da).A model for predicting the permeability coefficient of calcareous sand taking into account the salt content of transmitting solution has been proposed based on the current experimental studies on the influencing factors.The proposed model can provide a tool for assessing the permeability of artificially reclaimed islands and reefs in the South China Sea and analyzing the evolution of ground freshwater.