Characteristics and hysteresis of saturated-unsaturated seepage of soil landslides in the Three Gorges Reservoir Area, China

Abstract

Abstract The characteristics and hysteresis of seepage are critical for assessing the stability of creeping soil landslides after reservoir impoundment. First, field and laboratory tests were conducted to obtain the saturated permeability coefficient of 396 soil landslides within the Three Gorges Reservoir area and trends among these results were obtained through basic statistics. Second, geological surveys show that these soil landslides are mainly composed of mixed soil-rock structures. Thus, a pressure plate instrument was used for estimating the soil-water characteristic parameters of this unsaturated soil-rock mixture. Finally, the seepage characteristics and hysteresis of the soil landslides was analyzed through numerical simulation based on obtained permeability parameters. The results of this research show that the permeability level of the soil landslides in the Three Gorges Reservoir Area is, in overall terms, good and moderate, and the permeability of the soil landslides has certain spatial distribution characteristics. Also, it was found that the parameters a and m of the unsaturated Fredlund-Xing model became larger with increasing gravel particle size, dry density, and plasticity index of the soil particle; all with decreasing gravel content. Behavior of the n parameter shows an opposite trend. Furthermore, more than 90% of landslides show seepage hysteresis as their hysteresis parameter is less than 35. Finally, it was found that the hysteresis coefficient and slope gradient are the key parameters conditioning the hysteresis of soil landslides.