An experiment to induce a fluidized landslide by artificial rainfall was conducted on a natural slope at Mt. Kaba-san in the village of Yamato, Ibaraki Prefecture, Japan. The experimental slope was 30 m long, 5 m wide, and the average slope gradient was 33. A landslide initiated 24,627.5 s (410 m/27.5 s) after the start of sprinkling at a rainfall intensity of 78 mm/h. The landslide mass was 14 m long and 1.2 m deep (at maximum). It first slid, then fluidized, and changed into a debris flow. The travel distance was up to 50 m in 17s. The apparent friction angle of the fluidized landslide was 16.7. Formation of the sliding surface was detected by soil-strain probes. Motion of the surface of the failed landslide mass was determined by stereo photogrammetry.

During the 1920 Haiyuan earthquake, numerous catastrophic landslides were triggered in the loess 35 area in Northwest China. We investigated in detail a large example of these landslides, referred to as Dangjiacha 36 landslide in this paper. This landslide originated from a slope of about 20 degrees, and the displaced soil mass 37 traveled about 3200 m, damming a valley. We performed a field survey and found that standing water existed in 38 the landslide area and the loess had high porosity. We infer that it was the liquefaction of the water-saturated 39 loess layer rather than the suspension of silt in the pore-air in the loess that caused the great mobility of this 40 landslide. To test this inference, we performed undrained triaxial compression and ring shear tests on loess 41 samples to examine the shear behavior of loess saturated by either air or water. The test results showed that the 42 water-saturated loess soil was highly susceptible to flow liquefaction failure. Fast shear tests on naturally 43 air-dried loess samples revealed that the generated pore-air pressure was small under the "undrained condition" 44 and no significant reduction in the shear resistance was observed, implying that air entrapped in the loess was 45 unlikely to be the main contributor to the high mobility of this large-scale landslide. 46 47

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