接触角对张力计及轴平移技术测量非饱和土吸力的影响

Effects of contact angle on suction measurement with tensiometers and axis-translation technique in unsaturated soils

接触角变化将直接影响非饱和土中水–气交界面的性质。为研究张力计和轴平移技术测量吸力过程中接触角的变化情况及这种变化对测量结果的影响,以表面化学原理为基础,把退湿分为外力式退湿和蒸发式退湿2种形式;增湿分为外力式增湿和凝结式增湿2种形式。在此基础上分析退湿过程中,张力计和轴平移技术测量吸力时土体中的接触角特性。从理论上断定:退湿过程中,相同含水率下轴平移技术所测得的基质吸力要大于张力计所测;增湿过程中,相同含水率下轴平移技术测得的基质吸力则又小于张力计所测,并通过接触角测量试验和吸力测量试验验证了这一推断。2种测量方法在实际应用中应该对应不同的工况:对于雨水入渗,地下水位下降等非饱和土力学问题应该用轴平移技术试验结果;对于非饱和土的干缩问题则应该用张力计进行测量。

Contact angle change is going to affect the properties of water-vapour interface in unsaturated soil. In order to study the change of contact angle in suction measurement with tensiometers and axis-translation technique, and the effects of this change on the measurement, based on the principles of surface chemistry, drying process is divided into two parts, one is external forces pattern, another is evaporation pattern. Wetting process is also divided into two parts, external forces pattern and condensation pattern. According to this, in drying process, contact angle characteristics of suction measurement with tensiometer and axis-translation were analyzed. It can be concluded that, in drying process, matric suction measured by axis-translation is higher than tensiometers with the same water content. In wetting process, matric suction measured by axis-translation is smaller than tensiometers with the same water content. The conclusion is proved by contact angle measurement tests and matric suction tests. Different type of suction measurement method should be matched with different situations. The axis-translation should be used in some unsaturated soil problems such as rain infiltration, groundwater level decline. The tensiometers could be applied to drying shrinkage in unsaturated soil.