Abstract: Fourteen groups of slate samples are selected to take the mineral ingredient and microstructure test and make the lateral restraint swelling experiment and study the swelling characteristics and micromechanism of soft slate, taking slate form Zhijiang, Huaihua in Hunan province for example and considering the internal structure of soft slate and its swelling characteristics with water. The results indicate that the relationship between the lateral restraint expansion ratio and water absorption time exhibits exponential function. In the early stage of test, the expansion ratio increases with the extension of water absorption time; the growth rate is fast; and expansion ratio-time relationship curve is relatively steep. At the end of the test, the expansion tends to be stable; and the shape of the curve becomes from steep to gentle. The relationship between the expansion ratio and water absorption rate exhibits the power function. In the early stage of test, the growth rate is fast with the increase of water absorption rate, and gradually becomes lower until it tends to be stable in the late period of the test. The axial expansion rate greatly decreases in the form of logarithmic function with the increase of the axial load in the early stage of test, and gradually becomes stable in the late period of the test. When the angle α between the soft slate structural plane and axial direction changing from 0° to 90°, the expansion ratio reduces with the increase of angle α.

Key words: soft slate, swelling characteristics, micromechanism, nondimensionalization