Experimental study on SWCCs under equal stress and equal void ratio states

The existing laboratory test results in the literatures show that the void ratio is a direct factor affecting the soil-water characteristic curves (SWCCs), whereas the stress state is an indirect factor affecting SWCC, via void ratio. However, in the experimental investigations on the influence of void ratio on SWCCs in the literatures, only the initial void ratios of samples are controlled to keep the same or different, but the void ratios of samples during the SWCC tests are not controlled. In the present experimental study, the vertical stress and void ratio of samples after the unidirectional compression or compression-rebound along the scheduled paths are controlled to keep the same during the drying-wetting SWCC tests by means of a stress-dependent SWCC (SDSWCC) apparatus. The test results indicate that even if the vertical stress is identical (equal stress state), the SWCCs are different as long as the void ratio is different during the drying-wetting SWCC tests. As long as the void ratios of samples are consistent (i.e., equal void ratio state) during the drying-wetting SWCC tests, the change of vertical stress has little effect on SWCCs. Under an equal void ratio state, the drying/wetting rates and air-entry values (AEVs) of the samples are almost the same even if the applied vertical stresses are different. Under an equal stress state, the AEVs of samples decrease with the increasing void ratios of samples, and both hysteresis degree and area of hysteresis loop increase with the increasing void ratio of samples. This study provides valuable reference for one to choose the parameters for a SWCC model.