Experimental study on saturation and swelling-shrinkage characteristics of unsaturated expansive rocks

The engineering disasters caused by deformation and failure of expansive rocks occur frequently, and disaster-inducing mechanisms need to be further studied. In the present study, through indoor swelling and shrinkage tests and combined with the suction theory, the saturation and swelling-shrinkage characteristics of unsaturated and undisturbed strong expansive rock in Nanning were studied. The swelling rate tests were performed in both cases of different initial moisture contents without vertical load and different vertical loads, and the shrinkage tests were carried out under the condition that the samplesare sufficiently saturated and naturally dried. The research results indicate that, during the process of water absorption and swelling of the unsaturated expansive rock, both the saturation and the swelling rate show three-stage growth for two cases of no vertical load and the vertical load less than the expansive force, that the relationships between the saturation and the swelling rate of the two cases are respectively exponential and non-linear, and that the variation of the swelling rate lags behind that of the saturation, i.e., the expansive rock reaches saturation state first. When the vertical load is equal to the expansive force, the expansive rock absorbs water and reaches saturation state without volume variation. The variation tendency of the saturation of the expansive rock is influenced by the initial water content at the initial stage of water absorption, especially near the shrinkage limit, but the saturation after swelling stabilization is insensitive to the vertical load. It is also shown that, during the shrinkage process of initial saturated expansive rock, the saturation develops in a three-stage attenuation modeand there is a negative correlation between the saturation and the linear shrinkage. For unsaturated expansive rocks in Nanning area, the saturation changes while the swelling-shrinkage deformation almost keeps constant when the saturation is in the range of 80% and 90%. The corresponding research results can provide a scientific basis for reasonable construction of swelling-shrinkage constitutive model of expansive rocksand a guide for the evaluation of the stability of unsaturated expansive rock engineering. © 2020, Science Press. All right reserved.