无黏性土增湿-脱湿过程中接触角的特性

目的]研究粉土颗粒的接触角滞后特性,掌握土壤增湿或脱湿过程中的界面特性,为建立离散元接触模型提供相应的试验基础。方法]用躺滴法对土颗粒表面的初始接触角及动态接触角进行测量,用直接观测法对增湿和脱湿条件下土颗粒与孔隙水的接触角进行测量。结果]天然粉土的平均初始接触角为41.5°,远大于0,广泛用在具有连续表面固体动态接触角测量的3种方式仅有1种能测出土颗粒表面的动态接触角,且3种土样的后退接触角都大于0。初始接触角的小大对蒸发(脱湿)过程中土颗粒与孔隙水的接触角变化规律影响不大。同一试样,不同土颗粒与孔隙水间的接触角在脱湿过程中的变化规律并不一致,甚至会出现脱湿过程中接触角由小变大的情况。亲水土与斥水土的增湿模式差异较大,亲水土在增湿过程中先形成液桥再形成包裹土颗粒的液膜,而斥水土则是先在土颗粒表面形成液滴,再由液滴连接成包裹土颗粒的液膜。结论]土颗粒的接触角存在明显的接触角滞后现象,土颗粒表面的接触角和土颗粒间的接触角并不一致,实际应用时需要严格区分。

Contact Angle Characteristics of Cohesionless Soil During Humidification and Dehumidification

Objective] The contact angle hysteresis characteristics of silty particles were studied to understand the interface characteristics in the process of soil humidification or dehumidification, as well as to provide the corresponding experimental basis for the establishment of a discrete element contact model.Methods] The initial contact angle and dynamic contact angle on the surface of soil particles were measured by the sessile drop method, and the contact angles between soil particles and pore water under the condition of humidification and dehumidification were measured by the direct observation method.Results] The average initial contact angle of the natural silty soil was 41.5°, which was much greater than 0. Only one of the three methods widely used for measuring the dynamic contact angle of a continuous surface solid can measure the dynamic contact angle of the surface of soil particles with a receding contact angle of three soil samples greater than 0. The initial contact angle had little influence on the change rule of the contact angle between the soil particles and pore water during the process of evaporation (dehumidification). The change rule of the contact angle between different soil particles in the dehumidification process of the same sample was not consistent, and the contact angle may even change from small to large in the dehumidification process. The humidification modes of hydrophilic and hydrophobic soil were quite different. In the humidification process, pore water first formed a liquid bridge and then formed a liquid film covering the hydrophilic soil particles, while repellent soil first formed liquid droplets on the surface of the soil particles and then connected the droplets to form a liquid film covering the soil particles.Conclusion] The contact angle of soil particles lags significantly, and the contact angles between the soil particles and the surfaces of the soil particles are not consistent. Therefore, the contact angle must be strictly distinguished in practical applications.