Fuzzy judgment about the grade of shrink and expansion for the expansive soil in the subgrade

The swell shrink grade judgment of expansive soil is an important work for engineering construction in the expansive soil area. Based on the analysis of the existing swell shrink grade judgment methods and standards, this paper presents a fuzzy judgment model, including three performance indexes indirectly reflecting the expansion and shrink of soil such as liquid limit, plasticity index I p and shrink limit, and four direct relative indexes such as free expansion ratio F s, swell shrink ratio P c, swell shrink ratio e p50 under the pressure of 50 kPa and swell shrink total ratio e ps . The number of judgment indexes can be reduced under special condition, but that of indirect indexes should not be less than two, or that of direct indexes should not be less than three in shortage of indircet indexes. According to the theoretical analysis and experimental data, the weight of each index is established. The useful computer software of the judgment model has been programmed, and the method in the paper is proved credible through the calculation analysis and engineering test.