提出了用于非饱和原状黄土增湿的蒸汽增湿方法，给出了蒸汽增湿试验步骤，通过对比试验分析确定了适宜的试验参数，从增湿后水分分布是否均匀、土体密度是否改变等方面论证了蒸汽增湿方法的有效性。对含水率的测试结果表明，微波炉法测试结果能满足精度要求，酒精燃烧法在测试较高含水率时误差较大。进一步应用蒸汽增湿法得到的不同含水率原状土样测定了非饱和黄土冻融后的强度指标，揭示出当非饱和原状黄土含水率过低时，冻融作用对黄土的粘聚力值基本没有影响，当含水率较高时，经历冻融循环后黄土粘聚力值较冻融前降低，冻结温度越低以及冻融循环次数越多，降低值越大。经历冻融循环后黄土内摩擦角值较冻融前增加，冻结温度越低，增加值越大。在含水率较低时冻融循环次数几乎不引起内摩擦角值发生变化，在含水率较高时冻融循环次数越多，引起内摩擦角增加值越大。

A steaming humidifying method is proposed for humidifying unsaturated undisturbed loess sample; and the testing steps and testing parameters are given. The effectiveness of this method is verified by checking whether the distribution of moisture is uniform and whether the soil density has changed. The measured results of moisture content show that the results from microwave oven method meet the required precision; but the results from alcohol burning method have greater error at higher moisture contents. Strength index for unsaturated soil after freezing and thawing is measured on undisturbed soil samples with different moisture contents obtained by using the steaming humidifying method. The results reveal that the freezing and thawing effect has no influence on the cohesion of loess when the moisture content of unsaturated undisturbed loess sample is very low. However, when the moisture content is higher, the cohesion of loess decreases after freezing and thawing, the lower the freezing temperature and the more freezing-thawing cycles, the greater the decrease in cohesion. The internal friction angle of loess increases after freezing and thawing, the lower the freezing temperature, the greater the increase in internal friction angle. The internal friction angle has almost no change after freezing-thawing cycles when the moisture content is low. When the moisture content is higher, the more freezing-thawing cycles are, the greater the increase in internal friction angle is.

国家自然科学基金（No. 50678144）。