Heavy rainfall triggered loess–mudstone landslide and subsequent debris flow in Tianshui, China

A study of a flowslide with significant entrainment in loess areas in China

“…Figure shows the entrainment depth after simulation. The maximum entrainment depth is approximately 2 m. The average entrainment depth between x = 170 m and x = 730 m is approximately 1.8 m, which is very close to the estimation showing the entrainment depth at the track zone at approximately 2 m (Peng et al , ).…”

“…Longitudinal profile of the Dagou debris flow before and after the event (revised from Peng et al ., ). [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…After that point, the rate of the increase of total volume gradually decreased until the debris stopped. The total volume calculated is 213 × 10 3 m 3 , which is very close to the estimated total volume of the debris, 226 × 10 3 m 3 , including the volume of the debris at the deposition zone – namely, the track zones based on Peng et al .’s () description.…”

“…As shown in Figure 3, the flow channel is divided into the following main sections: source area, upper flow track zone, main flow track zone, and deposition area. The elevation of the slope is between 1090 and 1330 m. The average slope angle of the flow channel is about 29.2°, and slope length is around 1300 m. The landslides occurred due to heavy rainfall and occurred at an elevation of around 1210 and 1300 m. The flowslide started with a volume of approximately 1.6 × 10 5 m 3 , entrained material in flow track zone, and finally stopped with a volume of 2.26 × 10 5 m 3 (Peng et al, 2015). The erosion depth of the channel bed is about 1-3.5 m. The source material is mainly composed of weathered mudstone ranging from 2 to 5 m. The material lying on the flow channel mainly consists of Pleistocene loess (Q 3 ) with a thickness of approximately 2-6 m. It has loose structure and developed joint fissures.…”

“…Because the displaced landslide material transformed into a flowslide on its downslope movement with high mobility, hereinafter we term this landslide as Dagou flowslide. Although Peng et al (2015) studied the mechanism of the Dagou flowslide, and pointed out that liquefaction was the main reason for the high mobility of the Dagou flowslide, the downslope movement, especially the enlargement process due to the entrainment of debris on the traveling path of displaced landslide material had been less examined and remains unclear.…”