提高膨胀土自由膨胀率试验精度的研究
Study on improving Improving the accuracy of free swelling ratio test

【目的】分析膨胀土自由膨胀率试验的误差来源，为提高自由膨胀率试验的精确度提供依据。【方法】取陕西安康、陕西洋县和河北邯郸3种膨胀土，将安康素膨胀土筛分为3个粒组（粒径≤0.1 mm、0.1 mm＜粒径≤0.25 mm和0.25 mm＜粒径≤0.5 mm），分别测试3个粒组膨胀土的自由膨胀率；将占烘干安康膨胀土质量0.5%，1.0%，2.5%和5.0%的硅酸钠和0.1%，0.5%，1.0%和2.5%的阳离子型聚丙烯酰胺溶于纯水加入安康膨胀土中制成16种改性土样，研究粒度组成对改性土样自由膨胀率的影响；测试不同环境温度（10，15和25 ℃）下安康、洋县和邯郸膨胀土的自由膨胀率，并测试烘干土样是否在干燥器中冷却至室温对量土杯中土样质量的影响。【结果】粒径≤0.1 mm的安康膨胀土自由膨胀率为20%，0.25 mm＜粒径≤0.5 mm安康膨胀土的自由膨胀率为53%，结果相差33%。改性安康土样中，当硅酸钠质量为干素土的1.0%、阳离子型聚丙烯酰胺质量为干素土0.1%时，未控制粒组改性土样Ⅰ的自由膨胀率为23%，控制粒组改性土样Ⅱ（0.1 mm
【Objective】This study analyzed the error sources of free swelling ratio test to provide basis for improving its accuracy.【Method】The study took expansive soil samples from Ankang and Yangxian in Shaanxi and Handan in Hebei.The Ankang expansive soil samples were sieved to particle diameters (d≤0.1 mm,0.1 mm＜d≤0.25 mm,and 0.25 mm＜d≤0.5 mm),and the free swelling ratios were tested.The Ankang expansive soils were also modified with sodium metasilicate and cationic type polyacrylamide to 16 different soil samples to study the influences of gradation composition.The mass ratios of sodium metasilicate were 0.5%,1.0%,2.5%,and 5.0%,and the mass ratios of cationic type polyacrylamide were 0.1%,0.5%,1.0%,and 2.5%,respectively.Then the expansive swelling ratios of three kinds of expansive soils under 10,15 and 25 ℃ were tested and the quality of soil samples in the soil cup with and without being cooled in drying oven were investigated.【Result】The free swelling ratio of Ankang expansive soil with size of ≤0.1 mm was 20%.When the size was between 0.25 and 0.5 mm,the result was 53% with difference of 33%.For the modified soils,when mass ratio of sodium metasilicate was 1.0% and mass ratio of cationic type polyacrylamide was 0.1%,the free swelling ratio of modified soilⅠ and the soilⅡ were 23% and 40%.The next error source was the environment temperature.The result decreased by 43% when the temperature decreased from 25 ℃ to 15 ℃.Cooling had minor effects on mass of soil samples.【Conclusion】In order to increase the accuracy of the free swelling ratio,it is suggested to divide the soil samples to three size groups,0 to 0.1 mm,0.1 mm to 0.25 mm,and 0.25 mm to 0.5 mm,and the corresponding mass fractions should be 0－20%,20%－50% and 20%－50%,respectively.It is also helpful to cool the samples to 25℃