Preliminary analyses of a catastrophic rock avalanche that occurred in Ganluo County, Sichuan Province, China
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Yiding Zhao I Yao Shi I Fahong Wu
Preliminary analyses of a catastrophic rock avalanche that occurred in Ganluo County, Sichuan Province, China Introduction Due to the continuous rainfall from July to August 2019, the Aidai No. 2 Tunnel in Ganluo County, Sichuan Province, China (N29° 02′ 09.38″, E102° 47′ 59.09″) (Fig. 1), experienced a catastrophic rock avalanche at approximately UTC+8 12:44 on 14 August 2019. Because this rock avalanche was a typical rock avalanche, the failure event occurred quickly, which destroyed a 70-m long section of a railway line (Fig. 2a) at the foot of the mountain and fell into at the bottom of the valley of the Niri River (Fig. 2b). The rapid rock avalanche caused seventeen deaths and blocked ChengKun railway traffic. Immediately after this failure event, the Ministry of Emergency Management of the People’s Republic of China launched on-site emergency rescue and disaster mitigation operations. The azimuth of the sliding direction was approximately 112.5°. The rock debris mass was approximately 310-m long, 65-m wide and 10-m thick; its volume thus was estimated to be approximately 5.2 × 104 m3. Moreover, there remains a 1.5 × 104 m3 unstable rock mass perching atop the exposed bare earth (Zhu et al. 2020). Emergency response Because it was a large rock avalanche, the destruction was very serious (Fig. 3a). A mudslide occurred within the failure area on 4 August 2019, which caused the railway line to require urgent repair, before the rock avalanche occurred. Several workmen dredged mud in a culvert around the exit of the Aidai No. 2 Tunnel before the failure event occurred and were trapped by rocks. After the catastrophic disaster, the China State Railway Group Co., Ltd. rapidly ordered the highest-level emergency response. Many state units have been mobilized, including armed police, fire departments, medical care teams and geological survey teams from geological institutes. The central government and the local public council paid great attention to rock avalanche-affected areas (source: http:// m.sohu.com/a/335750933_677089). The rescue teams reached the affected area (Fig. 3b), and dozens of excavators were busy digging the debris deposits (Fig. 3c). Because of these local emergency responses, 11 survivors were successfully rescued from the rock avalancheaffected area shortly after the occurrence of the rock avalanche (source: https://www.huanqiu.com/). Furthermore, the rescue teams continued searching for potential survivors (Fig. 3d), and more than 300 nearby workers (in the nearby Aidai No. 3 Tunnel, who were there to make urgent repairs on railway line) and residents were urgently transferred to a safe area.
middle-alpine gorge surrounded by mountain peaks reaching approximately 1100 m a.s.l. The gorge is approximately 800-m deep in average. Stratified soils/rocks that remain at the place of the rock avalanche are defined as the Upper Sinian Dengying Formation (Z2 d), which is composed of siltstones and limestones. Figure 4 shows a very large pile of debris, suggesting that this
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