Abstract: Under the circumstance of single-dehydration process and dry-wet cycle process, the soil-water characteristic curves (SWCCs) of Chongqing compacted clay soil samples with different compaction degrees and different gradations were respectively obtained by means of temple apparatus and pressure plate apparatus. The testing results show that: (1) After compaction degree exceeding 90%, the linear sections of SWCCs of the soil samples with different compaction degrees close each other, which indicates that the SWCCs gradually tend to stability within the common matrix suction changing scope of this compacted clay soil. (2) With the increment of compaction degree, the hysteresis loops of dry-wet cycle process gradually move upward, and the SWCCs change from steep shape to mitigative shape; this indicates that the moisture in the soil samples is more difficult to be intaken or drained out, which is beneficial to the stability of subgrade. (3) Under the same water content, there is a boundary of compaction degree of 85% for the compacted clay soil, the matrix suctions of the soil samples with less than or more than this compaction degree basically do not change with compaction degree changing. (4) Under the same compaction degree and water content, the matrix suctions of the soil samples with more coarse grained soil are more smaller; and the hysteresis loops of SWCCs are also smaller, which indicates that the influence of dry-wet cycle process on coarse grained soil is smaller. Therefore, coarse grained soil is more suitable for use as fill material of subgrade.

Key words: subgrade, compaction degree, gradation, matrix suction, SWCC