Pore-pressure generation and fluidization in a loess landslide triggered by the 1920 Haiyuan earthquake, China: A case study

Abstract

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

Rock avalanche deposits store quantitative evidence on internal shear during runout

“…Most rock avalanche studies focus on shear at the rock avalanche base [e.g., Hungr, 2007], and many laboratory experiments simulate deformation on a discrete basal shear zone [e.g., Sassa, 1988;Sassa et al, 2004;F. Wang et al, 2014;G. Wang et al, 2014].…”

Effect of Dry-wet Cycle on the Formation of Loess Slope Spalling Hazards

“…Many loess slope spallilng hazards happened at Loess Plateau area of China due to the influence of heavy rainfall in the past twenty years (Figure 1) [2][3][4]. According to the previous research, loess slope spalling hazards can be triggered when water enters into loess slope at a shallow depth, while the saturated zone simultaneously rises from depth [5][6][7][8]. The matric suction in unsaturated loess decreased due to the increase of water contents, which induces the decrease of loess shear strength [9][10][11].…”

Analysis on the Development of Geohazards in Linwei District of Weinan City

“…About 12.4% disasters distribute on active fault zones in Linwei district, in which 60% collapse disaster, this is because the formation of active fault displacement field and deformation field, the formation of steep topography, rock and soil around the complete damage, loess structural joints and vertical joints of common cutting, forming massive rock mass, under gravity, it is easy to occur crack type collapse, lead to collapse disaster near fault fracture is developed. It is easier to develop the landslide in the Loess gully, about % landslide, there are two types valley, V and U type Valley, gully slope at between 30 and 50 degree, because the loess has a very strong vertical nature, not easy to collapse at this angle; the effect of seasonal water erosion in the slope toe, stress redistribute constantly, it is easy to format tensile cracks in the top of the hill, in the rain or induce in earthquake [12][13][14][15][16]. And u develop in the Loess Plateau valley, the reason of the development of landslide is that underground water uplift on tableland irrigation slope, the underlying mud sandstone softening, soil weight increased and the strength resistance decreased.…”