Abstract: Loess is highly structured and water sensitive. Water-induced geohazards due to human activities and natural factors are of great concern, especially the loess slope with a saturated base. The failure process of a bottom-saturated loess slope was reappeared in this research based on a centrifuge test using the intact loess model. Monitored by the video, the PIV technique and the pore water pressure and soil pressure, the failure mode of the loess slope was analyzed. The main conclusions are as follows. The bottom of the model is thoroughly saturated when the acceleration is increased to 80g and there exists multiple failure forms on the slope model including sliding failure, collapse failure and internal subsidence failure. The PIV results indicate that the fractures on the surface of the model occur before the sliding failure and the collapse failure. The sliding failure and collapse failure both occur on the high pore-water pressure area though the pore-water pressure distribution is nonuniform at the bottom of the model. The sliding failure process in the model is the same as that of the field landslide following the process of base saturation, tensile fractures occurring, small backward sliding, water level increasing and large backward sliding. The results can provide reference for the model test study on undisturbed loess and the multi-failure mechanism of in-situ landslide especially in the long term irrigated loess areas.

Key words: bottom-saturated slope, loess landslide, intact soil, centrifuge test