表面张力与接触角对膨胀土干缩开裂影响的试验研究

用悬滴法对纯水、酒精溶液和肥皂水(表面活性剂)3种液体的表面张力进行测量,比较3种液体表面张力的大小;用躺滴法测量混有十八胺的两种土样的接触角。在此基础上,针对不同表面张力和接触角的膨胀土试样进行收缩开裂试验。试验结果表明:孔隙水表面张力和接触角对膨胀土的收缩开裂有重要影响。表面张力越小的试样,其最终收缩开裂裂隙度越小,但在裂隙发展阶段,脱湿时间相同时,孔隙水表面张力小的土样其收缩开裂裂隙度有可能大于表面张力较大的土样。增大土颗粒与孔隙水间的接触角可以很好的抑制膨胀土的收缩开裂,接触角越大,相同的脱湿时间下土体的收缩开裂裂隙度越小。减小孔隙水表面张力或增大接触角都会使土体中的弯液面曲率半径增大,从而减小土体中的基质吸力。接触角的增大还有可能使弯液面由凹变凸,基质吸力会因此消失,从而很好的抑制膨胀土开裂。

Effects of pore water surface tension and contact angle on dry-shrinkage cracking of expansive soils

The surface tensions of water, alcoholic solution and suds (surfactant) are measured by using the pendent drop method, and then their values are compared. The contact angle of soil samples is measured by means of the sessile drop method, and the samples are mixed with octadecylamine. Based on the results, the tests on dry-shrinkage cracking are conducted on expansive soil samples with different pore water surface tensions and contact angles. The results indicate that the surface tension and contact angle have a major impact on the dry-shrinkage cracking of expansive soils. The soil samples with a less surface tension have a less final crack ratio. In the phase of cracking development, the samples with a lower surface tension have a higher crack ratio during the same amount of drying time. Increasing the contact angle of soil particles and pore water can hold back the dry-shrinkage cracking in expansive soils. For the soil samples during the same drying time, a larger contact angle will cause a smaller crack ratio. Both decreasing the surface tension and increasing the contact angle lead to the increase of the radius of curvature in pore fluid, and the matric suction thus decreases. Meniscus may become convex because of the larger contact angle, and the matric suction will disappear in this situation.