Abstract: It is very important to study the threedimensional expansion characteristics of expansive soils for the stability analysis of slopes with expansive soils. In this experiment, an inhouse developed three-dimensional expansion testing device was used to test the three-dimensional expansion rate in the laboratory conditions of the grey-white expansive soil samples in Nanning. The results show that:  after soaking, the expansion rate of expansive soil samples can be divided into three stages: the rapid expansion, the slow expansion and stabilization phases. The 80%~90% of the entire expansion process can be completed within three hours, and the overall expansion can be generally completed in six hours. The vertical expansion rate of the sample is larger than the lateral expansion rate, and the lateral expansion rates in two different directions are roughly equivalent. The ratio R0 of expansion rate to vertical expansion rate varies with the initial dry density, ranging from 0.61 to 0.82. Under the same initial moisture content condition, R0 increases with the increase of dry density, which indicates that the greater the dry density of expansive soil, the weaker the anisotropy of the sample. Under the same initial moisture content condition, the expansion rate increases with the increase of dry density of soil sample, and the higher the moisture content, the smaller the change rate of vertical expansion rate with the initial dry density; Under the same initial dry density, the expansion rate decreases with the increase of initial water content, and the higher the dry density, the higher the vertical expansion rate with the initial water content.

Key words: Expansive Soils, Three-way Expansion Test Device, Vertical Expansion Rate, Lateral Swelling Rate