Abstract: This research aims at the stability of expansive soil which were collected from the subgrade slope of expansive soil in Yanbian region of Jilin Province. The physicochemical property， soil grain， mineral composition and the expansion property of the specimen were tested. The pore structure characteristics were studied using mercury injection experiment. Furthermore， the soil pores were divided into four size intervals， i.e.， big pores， moderate pores， micro-pores and ultra-micro pores by using fractal geometry theory. The study indicated that five specimens were identified as slightly-expansive soil by expansibility testing. Pore sizes of the high expansive soil mainly fall in between micro-pores and ultra-micro pores， while pore sizes of the weak expansive soil mainly fall in between big and moderate pores.

Key words: expansive soil, pore distribution, fractal geometry, mercury injection test, expansion mechanism