| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 96 === The subgrade soil was treated as unsaturated. When the subgrade soil is affected by the nature water cycle of wetting and drying, the water content of subgrade soil would be changed. This result often causes changes of the matric suction and soil parameters. The wetting apparatus developed by Liao(2006), and the drying apparatus developed in this study were used to conduct the water content simulation. The results were then used to study the relationship between the matric suction and the soil parameters under various wetting-drying paths. The results show more significant influence on the matric suction due to changes in soil parameter at the beginning of the wetting process. When the water content approaches the equilibrium moisture content, this influence becomes less significant. Upon drying, water content quickly to decrease causing significant changes in soil parameters and sudden increase in matric suction. This behavior fall in the transition zone defined by Vanapalli(1999). Test results of soil-water characteristic curves show that drying curve and the wetting curve do not follow at the same path, probably due to the “hysteretic effect”. This research also studied the effect of compaction energy（inclouding the modified、standard and reduced energy）on the matric suction. Test results show that when the water content is below 20%, matric suction of the subgrade soil clearly increase with compaction energy.
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