Factors influencing accuracy of free swelling ratio of expansive soil

Many geotechnical structures, such as the subgrade of high-speed railway, are extremely sensitive to micro deformations. As one of the most commonly used indexes in China to evaluate the potential swelling level of expansive soils, the effectiveness and accuracy of free swelling ratio should be highly required. However, due to the deficiency of geotechnical test regulations for the free swelling ratio test, non-negligible variation difference is often observed among the test results of the same type of soil samples. Thus, a series of laboratory tests are conducted to figure out the influences of soil particle size, initial soil temperature, and wet-dry circulation on the free swelling ratio of expansive soils. The results show that the initial soil temperature exerts an obvious influence on free swelling ratio and a relative weak influence on soil mass of expansive soil with the micro soil particle size (d<0.075 mm), and the correlation becomes unclear when soil particle size is within the range of 0.075 mm <= d<0.500 mm. A larger particle size of expansive soils induces a larger free swelling ratio and soil mass in the soil measuring cup regardless of initial soil temperature. However, the enlarging amplitude decreases as the particle size of expansive soils increases. There is a progressive enlargement of free swelling ratio at the first two wet-dry cycles and then it attenuates gradually when the number of wet-dry cycles further increases.