两种pH水环境干、湿循环作用对泥质砂岩的侵蚀研究

Erosion analysis of argillaceous sandstone under dry-wet cycle in two pH conditions

选取三峡库区某边坡的泥质砂岩为研究对象,分别对pH=3和pH=7溶液下干、湿循环作用的泥质砂岩进行电镜扫描试验(SEM)、4种围压下的三轴压缩试验,通过MATLAB软件处理得到不同pH值和干、湿循环次数下SEM图像的骨架面积比和分形维数。研究表明:在相同的干、湿循环次数下,pH=3酸性环境下的分形维数比p H=7的要大;分形维数与吸水率成正比例相关;与骨架面积、凝聚力成反比例相关;泥质砂岩在干、湿循环作用下的临界骨架面积比为0.55左右;提出了泥质砂岩在干、湿循环作用下的侵蚀度概念,计算并拟合了泥质砂岩的侵蚀度随干、湿循环次数变化的关系曲线;推导出凝聚力的损伤变量公式,为研究不同pH水环境对岩石的侵蚀作用提供参考依据。

Argillaceous sandstone from a slope in Three Gorges Reservoir is investigated. A series of tests including triaxial compression test under four confining pressures, scanning electron microscope（SEM） is conducted on the sandstone samples subjected to cyclic wetting-drying in different p H conditions（p H=3, p H=7）. The area ratio of skeleton and fractal dimension of images obtained by SEM under different p H conditions and different times of dry-wet cycle is obtained by MATLAB. The study shows that when samples suffer the same times of dry-wet cycle, the fractal dimension in acidic conditions（p H=3） is bigger than that in neutral conditions（p H=7）. Also, it is indicated that the fractal dimension is proportion to water absorption rate and inversely proportion to skeleton area and cohesion. And the critical area ratio of skeleton of argillaceous sandstone subjected to alternation of wetting and drying is calculated to be 0.55. A concept of erosion degree is defined for argillaceous sandstone subjected to dry-wet cycles. Then a relation curve between the erosion degree of argillaceous sandstone and times of dry-wet cycle is obtained by fitting. Damage variable formula of cohesive force is derived. The study results provide theoretical basis for erosion of argillaceous sandstone in different p H conditions.