孔隙溶液对膨胀土力学性质影响

Effects of pore solution on mechanical properties of expansive soil

为研究孔隙溶液的浓度和组分对膨胀土力学性质的影响规律,对含不同浓度的Na Cl、Ca Cl_2溶液的膨胀土进行自由膨胀率试验和直剪试验。试验结果表明,随着溶液浓度的增大,自由膨胀率先快速降低,再平缓下降;浓度相同时含Na Cl溶液的膨胀土其自由膨胀率比含Ca Cl_2溶液的稍大,随着溶液浓度的增大,土样的剪切强度和黏聚力降低;溶液对内摩擦角的影响较小。分析试验结果认为,膨胀土表面具有固定的负电荷,颗粒表面会形成双电层;随着盐溶液浓度的增大,双电层厚度降低,颗粒间斥力减小,使得粒间应力增大,土颗粒沉降,降低了自由膨胀率;阳离子化学价越高,半径越大,对双电层的影响越显著,因此Ca Cl_2溶液比Na Cl溶液对自由膨胀率的影响更大。另一方面,盐溶液会改变膨胀土的结构,使其从集聚状变成絮凝状。盐溶液增大粒间应力,使膨胀土的强度增大,结构的改变会使强度降低,上述两种影响因素对强度呈相反的趋势,对该广西膨胀土,结构的作用超过了粒间应力的影响。

To investigate effects of the concentration and composition of the pore solution on the mechanical properties of the expansive soil, free swelling rate tests and direct shear tests are performed on Guangxi expansive soils containing different concentrations of Na Cl and Ca Cl_2 solutions. The experimental results show that with the increase of solution concentration, the free swelling rate decreased rapidly and then decreased gradually. When the concentration is the same, the free swelling rate of expansive soil containing Na Cl solution is slightly larger than that of Ca Cl_2 solution; the strength and the cohesive of soil decrease with the increase of concentration; however, the influence of solution concentration on the internal friction angle is smaller. Analysis of the test results shows that the expansive soil surface has a negative charge fixed, the particle surface will form electric double layer; as the concentration of salt solution increases, the thickness of the double layer decreases, the repulsion between particles decreases, the intergranular stress increased, soil particle sedimentation, reducing the free swelling rate; meanwhile, the higher cationic chemical price, the greater cationic radius, the more significant effects on the double layer; therefore Ca Cl_2 solution has a greater effects on the free swelling rate than Na Cl solution. On the other hand, the salt solution can change the structure of expansive soil from agglomeration to flocculation. The salt solution will increase the intergranular stress, increasing the strength of the expansive soil; however, structural changes can reduce the strength. The above two influencing factors have the opposite trend to the strength, for Guangxi expansive soils, the effect of the structure larger than the effect of intergranular stress.