Mechanism of a catastrophic landslide occurred on May 12, 2019, Qinghai Province, China
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Min Xia I Guang Ming Ren I Xi Li Yang
Mechanism of a catastrophic landslide occurred on May 12, 2019, Qinghai Province, China
Abstract On May 12, 2019, a landslide occurred near a construction site of a reservoir dam along the left bank of the Wulong River, Qinghai Province, China. Video footage showed that the entire failure process of the landslide lasted for 15 min. Although an excavator that parked on the foundation pit was buried and the Wulong River was blocked, this landslide did not cause any casualties. Based on field investigations, 3D laser scanning, unmanned aerial vehicle observations, and borehole surveys, this study aims to reveal the cause and initiation mechanisms of the landslide. The landslide developed on a typical dip slope with thick-bedded conglomerates intercalated with a few mudstone layers. The slide mass mainly consisted of conglomerates with a dip angle varying from 20 to 40°, failing along bedding plane contacts with the underlying muddy intercalation. Numerous tension cracks had developed in the upper part of the slope due to stress relaxation during the process of bank slope evolution associated with rapid river incision. These cracks damaged the integrity of the rock mass and promoted rapid rainfall infiltration. The water infiltrated into the slope and deteriorated the mechanical properties of the rock mass, which resulted in long-term deterioration of the slope stability conditions. In addition, the temperature of Tongren County was below zero for 5 months in a year, hence the freeze–thaw cycle of the water filled in the cracks would have reduced the shear strength further. There were 10 days of continuous rainfall before the landslide occurred, and the cumulative precipitation in 2018 and 2019 was also significantly more than that of previous years. Three primary factors are involved in the landslide event: (1) thick-bedded conglomerates intercalated with a few mudstone layers with contrasts in strength, (2) development of numerous relaxation cracks, and (3) long-term rainfall accumulation. Keywords Landslide . Initiation mechanism . Wulong River . China Introduction Slopes with interbedded rock layers are widely distributed around the world and have been the source of numerous landslide disasters. Heim (1932) describes landslides involving the conglomerates of the subalpine Molasse, of which the Goldau rockslide is probably the best-known slope failure event. This rockslide occurred in 1806 and claimed 457 lives. The rockslide involved 20 million m3 of rock and was triggered by a rapid snowmelt coinciding with heavy rainfall (Eisbacher and Clague, 1984). The slide mass primarily consisted of conglomerates with a dip angle varying from 15 to 30°, purportedly failing along bedding plane contacts with the underlying marls. Furthermore, Eberhardt et al. (2005) studied the instability mechanisms of a complex slope near the town of Rufi in the Canton St. Gallen in northeastern Switzerland, involving
interbedded conglomerates and marls related to coupled geological, geomechanical, and
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