含盐量对亚硫酸盐渍土抗剪强度影响的试验

Effect of salt content on shear strength of sulfurous saline soil

为探讨含盐量对盐渍土抗剪强度的影响,该研究对采自于青海柴达木盆地大柴旦盐湖地区的盐渍土进行了洗盐试验以获得素土试样;根据该区盐渍土类型及盐渍化程度,在洗盐后土体中分别加入不等量的无水硫酸钠(Na2SO4),以获得不同含盐量的人工配制硫酸盐渍土,并对上述不同含盐量的人工配制硫酸盐渍土开展室内直接剪切试验。试验结果表明,洗盐试验后土体中的易溶盐离子含量及p H值均显著低于洗盐前盐渍土;当土体密度和含水量分别为1.41 g/cm3和25.68%时,洗盐后土体粘聚力c值和内摩擦角φ值分别为14.8 k Pa和26.5°,均高于洗盐前盐渍土的粘聚力值(6.7 k Pa)和内摩擦角值(24.6°);不同含盐量梯度条件下的人工配制硫酸盐渍土的粘聚力和内摩擦角,随土体含盐量增加均表现出先减小后增加的变化特征。当含盐量由0.74%增至5.17%时,人工配制硫酸盐渍土粘聚力c值和内摩擦角φ值均呈逐渐减小的变化规律,当土体含盐量由5.17%增至14.17%时,人工配制硫酸盐渍土粘聚力c值和内摩擦角φ值均表现出增加的变化规律,且当含盐量为5.17%时,其粘聚力c值和内摩擦角φ值分别为8.3 k Pa和26.1°,均为最小值,即该值对应的含盐量值即为人工配制硫酸盐渍土的含盐量阈值。本项研究成果对于进一步探讨含盐量变化对盐渍土抗剪强度影响,及含盐量变化与盐渍土粘聚力和内摩擦角之间的关系等方面具有理论研究价值和实际意义。

To investigate the influence of salt content on the shear strength of salinized soil as well as the relationship between cohesion force, internal friction angle and salt content, the Da Qaidam Salt Lake and surrounding areas located in the Qaidam Basin, Qinghai Province, have been selected as the testing area. The salinized soil samples at 0~30 cm beneath the ground surface have been collected and meanwhile salt-leaching tests on these collected salinized soil samples have been conducted to produce salt-leached soil. On the basis of the procedures mentioned above, according to the type and salinization degrees of the collected salinized soil, anhydrous sodium sulphate（ Na2SO4） with different masses has been separately added into the salt-leached soil to make artificial sulphate saline soil with 6 salt gradients, and then direct shear tests have been conducted on these artificial sulphate saline soil to further investigate the influence of salt content on the shear strength, as well as the shear strength indices such as cohesion force and internal frictional angle. The results are as follows： after salt-leaching tests, soluble salt ions′ content and p H value are markedly lower than the counterparts before salt-leaching. Total ion content decreases from 2.165 0% to 0.74%, which is lower than the value before salt-leaching and p H value decreases from 8.65 to 8.01. Moreover, after salt leaching, soil grain composition has changed by some extent,sand is reduced from 33.0% to 31.3%, silt is declined from 55.2% to 54.0%, and clay particle is increased from 11.8% to14.7%, respectively. Meanwhile, as the soil density and moisture content are 1.41 g/cm3 and 25.68% respectively, the cohesion force and internal friction angle for salt-leached soil are 14.8 k Pa and 26.5°, which are higher than the counterparts（6.7 k Pa and 24.6°, respectively） for salinized soil before salt leaching. With different salt contents, the cohesion force and internal frictional angle of the artificially salinized soil exhibit an trend of initial decreasing and then increasing as the salt content increases. And further study results show when salt content increases from 0.74% to 5.17%,the cohesion force and internal frictional angle for artificially salinized soil gradually decline, and as salt content increases from 5.17% to 14.17%, the cohesion force and internal frictional angle for artificially salinized soil increase gradually. And as salt content is 5.17%, the corresponding cohesion force and internal frictional angle for artificially salinized soil are 8.3k Pa and 26.1°, respectively, which are both the minimum values. So the corresponding salt content value is the threshold value of the artificial sulphate saline soil, which indicates that there exists a threshold value for sulfate saline soil. As the salt content is below this value, the cohesion force and internal friction angle decline with salt content increasing, and as the salt content is beyond this value, the cohesion force and internal friction angle increase with salt content increasing. The achievement has theoretical and practical significance in further exploring the influence of various salt contents on the cohesion force and internal friction angle as well as on the shear strength of the salinized soil. And this study can also serve as a basis for the further studies on the engineering characteristics of salinized soil.