geosciences

Communication Investigation of Landslides that Occurred in August on the –Kunming Railway, ,

Qian Zheng 1,2, Shui-Long Shen 1,2,* , An-Nan Zhou 3 and Hao Cai 2,4

1 Department of Civil and Environmental Engineering, College of Engineering, Shantou University, Shantou 515063, China; [email protected] 2 Key Laboratory of Intelligent Manufacturing Technology (Shantou University), Ministry of Education, Shantou University, Shantou 515063, China; [email protected] 3 Civil and Infrastructure Engineering Discipline, School of Engineering, Royal Melbourne Institute of Technology (RMIT), Victoria 3001, Australia; [email protected] 4 Department of Computer Engineering, College of Engineering, Shantou University, Shantou 515063, China * Correspondence: [email protected]; Tel.: +86-754-8650-4551

 Received: 10 October 2019; Accepted: 23 November 2019; Published: 26 November 2019 

Abstract: This paper reports on a large-scale landslide with a movement of 48 thousand m3 of soil and rock that occurred in Sichuan, China. This catastrophic landslide occurred in Aidai village, Ganluo County, at 12:44 on 14 August 2019, blocking a section of the railway between Lianghong station and Aidai station. This landslide resulted in 12 deaths and five people missing. This report describes the preliminary investigation, the rescue activity, topographic survey and analysis as well as the main predisposing and triggering factors. The combined effects of steep topography, continuous rainstorms, floods eroding the foothills of the mountain and human activity were the main influencing factors that triggered this landslide. To reduce the possibility of casualties resulting from large geological disasters, such as landslides and mudslides, in this region in the future, some recommendations are proposed to systematically reduce potential human casualties and economic losses.

Keywords: landslide; Ganluo; geology and landforms; rainstorm; recommendations

1. Introduction Thousands of landslides happen every year worldwide causing deaths and large damages [1–3] among which China is one of the most seriously affected countries [1]. It is reported that 130 million people were affected by natural disasters in China in 2018 which killed 589 people, left 46 people missing, and caused direct economic loss of 264.46 billion yuan. According to statistics, 35.3 million people suffered floods and geological disasters nationwide which resulted in 338 deaths, 42 persons missing, and 1.42 million people urgently being relocated. In total, 64,000 houses collapsed, and, in addition, 139,000 were seriously damaged and 650,000 more were generally damaged. Direct economic losses reached 106.05 billion yuan (approximately $15.06 billion USD) [4]. In addition, the total number of deaths from snow, drought, typhoon, and earthquake in 2018 was 103, and the total economic loss was 116.03 billion yuan (approximately $16.5 billion USD) which together is equivalent to the losses by floods and geological disasters. Landslides have been one of the main factors impeding state economic development, particularly in the western regions of China. Landslides have become a serious threat owing to the special landform and geological conditions prevailing in western China [5]. Even though rockslides and avalanches

Geosciences 2019, 9, 497; doi:10.3390/geosciences9120497 www.mdpi.com/journal/geosciences Geosciences 2019, 9, 497 2 of 12 occur in remote mountainous areas [6], they still commonly cause traffic jams, block river flow systems, destroy factories and mines, bury villages and towns [7–9], and even result in significant human casualties. Landslides have drawn a tremendous amount of attention from many researchers, with efforts focused on finding methods to forecast their occurrence or to assess the related hazards [10–12]. Effective long-term participation of the emergency management department (EMD) and local residents continues to be an enormous challenge in disaster risk mitigation in landslide-prone areas. Currently, early warning systems (EWSs) and post-disaster management systems are the most significant methods to reduce casualties and economic losses in high-occurrence disaster zones for landslides. The Norwegian water resources and energy directorate (NVE) [13], which is a part of the state responsibility management department, has been developing an integrated regional EWS for landslides. The objective of this system is to analyse, predict, and follow the hydrological and meteorological conditions available to trigger landslides. In addition, the system can warn the authorities of potential catastrophic events in advance. In South Korea, Dongyeob et al. [14] proposed a landslide EWS based on sensors in high landslide-prone sites in urban areas. The sensors are an integral part of the prevention and control system for sediment-related disasters. In Ethiopia, the Abay gorge [15] witnesses frequent landslides during the rainy season along Gohatsion–Dejen road. Therefore, the researchers divided the land surface there into regions of different disaster levels and conducted landslide hazard zonation (LHZ) mapping in the Abay gorge, combined with remote sensing (RS) and geographic information system (GIS) techniques. Despite efforts made by researchers and governments worldwide, a series of continuous landslides occurred in the village of Aidai, Ganluo County, Sichuan Province, in 2019. The objective of this study was to conduct a preliminary investigation into this specific catastrophic landslide in Aidai including the actual occurrence of the landslide, rescue efforts and the analysis of causes and influential factors.

2. Investigation A catastrophic landslide occurred in Aidai village, Ganluo County, at 12:44 on 14 August 2019, which blocked a section of the railway line between Lianghong and Aidai stations (see Figure1). Ganluo County is located at the southwest of Chengdu, the capital of Sichuan, China. This section is a part of the railway between Chengdu and Kunming which is the only railway connecting China’s southwest region to the other regions. In this landslide event, approximately 48,000 m3 of earth and rocks slid down the mountain from a height of about 190 m (the vertical distance between the highest point of the landslide and the railway). This landslide happened close to Aidai railway tunnel 2, and its duration was estimated to be approximately 6 s [16]. Figure2a,b show photographs before and after the landslide, respectively. Figure3 presents an overall view of the site after landslide A (14 August 2019) occurred. The total length of the landslide was estimated to be approximately 316 m. The width of the main scarp was 96 m at an altitude of 1182 m. The width of the landslide toe was approximate 78 m at an altitude of 979 m. The minimum width of the main body was estimated to be approximately 31 m at an altitude of 1047 m. The main body buried a 70 m stretch of the railway line at an altitude of 964 m. The area of main body was 20769 m2 (see Figure4b). In addition, earth and rocks flowed into the Niri River and destroyed the surrounding houses, and the debris flowed into the adjacent tunnel outlet 2. Landslide A resulted in 12 deaths and five people missing. Furthermore, this important railway track had to be closed until 30 August. Next to where landslide A occurred, a mudslide B occurred on 4 August 2019, which deposited approximately 4000 m3 of mud. Most of the dead and missing from landslide A were workers and railway staff working at the site to clear the culverts blocked by mudslide B. Geosciences 2019, 9, 497 3 of 12

Figure 1. (a) Location of Sichuan; (b) location of Aidai village; (c) Satellite image depicting the location Figure 1. (Figurea) Location 1. (a) Location of Sichuan; of Sichuan; (b) location (b) location of of Aidai Aidai village;village; (c )( Satellitec) Satellite image image depicting depicting the location the location of the landslideof the landslide and nearby and nearby topo topographygraphy (A (A depicts depicts the landslidelandslide that that occurred occurred on 14 on August 14 August 2019). 2019). of the landslide and nearby topography (A depicts the landslide that occurred on 14 August 2019).

FigureFigure 2. (a) 2.Satellite(a) Satellite imagery imagery before before the the landslides. landslides. ((bb)) PhotoPhoto taken taken after after the landslides.the landslides. (A): The (A): The landslidelandslide on 14 onAugust 14 August 2019. 2019. (B) (BThe) The landslide landslide on on 4 August 2019, 2019, recreated recreated based based on Reference on Reference [17]. [17]. Figure 2. (a) Satellite imagery before the landslides. (b) Photo taken after the landslides. (A): The landslideFigure on 3 14presents August an 2019. overall (B) Theview landslide of the site on 4after August landslide 2019, reAcreated (14 Augu basedst 2019) on Reference occurred. [17]. The total length of the landslide was estimated to be approximately 316 m. The width of the main scarp wasFigure 96 m 3 at presents an altitude an ofoverall 1182 metres.view of The the width site after of the landslide landslide A toe (14 was Augu approximatest 2019) occurred.78 m at an The totalaltitude length of of 979 the metres. landslide The wasminimum estimated width to of be the approximately main body was 316 estimated m. The to width be approximately of the main 31scarp wasm 96 at m an at altitude an altitude of 1047 of metres. 1182 metres. The main The body width buried of athe 70 landslidem stretch oftoe the was railway approximate line at an altitude78 m at an altitudeof 964 of metres. 979 metres. The area The of mainminimum body waswidth 20769 of them2 (see ma inFigure body 4b). was In addition,estimated earth to be and approximately rocks flowed 31 m atinto an altitudethe Niri Riverof 1047 and metres. destroyed The themain surrounding body buried houses, a 70 m and stretch the debris of the flowed railway into line the at adjacent an altitude of 964 metres. The area of main body was 20769 m2 (see Figure 4b). In addition, earth and rocks flowed intoGeosciences the Niri 2019 River, 9, x; anddoi: FOR destroyed PEER REVIEW the surrounding houses, and the debris www.mdpi.com/journal/geosciences flowed into the adjacent

Geosciences 2019, 9, x; doi: FOR PEER REVIEW www.mdpi.com/journal/geosciences Geosciences 2019, 9, x FOR PEER REVIEW 2 of 5 Geosciences 2019, 9, x FOR PEER REVIEW 2 of 5 tunnel outlet 2. Landslide A resulted in 12 deaths and five people missing. Furthermore, this tunnel outlet 2. Landslide A resulted in 12 deaths and five people missing. Furthermore, this important railway track had to be closed until 30 August. Next to where landslide A occurred, a important railway track had to be closed until 30 August. Next to where landslide A occurred, a mudslide B occurred on 4 August 2019, which deposited approximately 4000 m3 of mud. Most of the mudslide B occurred on 4 August 2019, which deposited approximately 4000 m3 of mud. Most of the dead and missing from landslide A were workers and railway staff working at the site to clear the Geosciencesdead and2019 missing, 9, 497 from landslide A were workers and railway staff working at the site to clear4 ofthe 12 culverts blocked by mudslide B. culverts blocked by mudslide B.

Figure 3. An overview of the landslide site. (A) The landslide on 14 August 2019. (B) The landslide Figure 3. An overview ofof thethe landslidelandslide site. site. ( A(A)) The The landslide landslide on on 14 14 August August 2019. 2019. (B )(B The) The landslide landslide on on 4 August 2019, recreated based on Reference [18]. on4 August 4 August 2019, 2019, recreated recreated based based on Referenceon Reference [18 ].[18].

Figure 4. (a) 3D model taken from Google Earth before the landslide. ( (A)) The The landslide landslide on on 14 14 August. August. Figure 4. (a) 3D model taken from Google Earth before the landslide. (A) The landslide on 14 August. ((bb)) AA photophoto takentaken afterafter thethe landslidelandslide (recreated(recreated basedbased onon ReferenceReference [[19]).19]). Data resources were fromfrom (b) A photo taken after the landslide (recreated based on Reference [19]). Data resources were from Reference [[20].20]. Reference [20].

2.1. DataThis Sourcelarge-scale landslide is believed to be the most serious landslide disaster ever to hit Ganluo This large-scale landslide is believed to be the most serious landslide disaster ever to hit Ganluo County since 1981. The joint-force rescue operation involved more than 750 personnel including CountyTo analysesince 1981. the event,The joint-force the weather rescue data operat recordsion of Ganluoinvolved County more than were 750 collected personnel from theincluding public

records of Sina Weather (http://weather.sina.com.cn/ganluo) which included the annual average rainfall in Ganluo, the monthly average highest temperature, the monthly average lowest temperature and the daily rainfall recorded by the weather channel 20 days prior to the disaster. Geosciences 2019, 9, 497 5 of 12

Geosciences 2019, 9, x FOR PEER REVIEW 5 of 12 2.2. Rescue Effort 2.2. Rescue Effort This large-scale landslide is believed to be the most serious landslide disaster ever to hit Ganluo CountyThis since large 1981.-scale landslide The joint-force is believed rescue to operationbe the most involved serious landslide more than disaster 750 personnel ever to hit including Ganluo Cfirefighters,ounty since armed 1981. police The joint and- militiamenforce rescue who operation came from involved Ganluo more County than as 750 well personnel as other cities including such firefighters,as Chengdu armed and . police and militiamen Concurrently, who to came rescue from the Ganluo buried C people,ounty as 39 well pieces as other of mechanical cities such asrescue Chengdu equipment and Panzhihua. were dispatched Concurrently, which included to rescue seven the buried rail cars, people, eight 39 sets pieces of excavators of mechanical to excavate rescue equipmentthe stocks, were three dispatched sets of radar which life included detectors, seven audio rail and cars, video eight detectors sets of excavators and lighting to excavate equipment. the Anstocks, additional three sets 40 ofunits radar of hydraulic life detectors, fracturing audio equipment and video detectors were also and deployed. lighting In equipment. addition, Anthe additionalemergency 40 management units of hydraulic department fracturing arranged equipment three were search also and deployed. rescue In dogs addition, to help the the emergency rescuers managementsearch for missing department persons arrangedand used drones three search for real-time and rescue monitoring dogs ofto the help changes the rescuers happening search on thefor missingsurrounding persons mountains and used and the drones landslide for real face-time (see Figure monitoring5). of the changes happening on the surrounding mountains and the landslide face (see Figure 5). (a) (b)

Figure 5. Rescue activities: ( (aa)) e excavatorsxcavators clearing clearing r rubbleubble (Picture (Picture source source from from [21] [21])) and ( b) workersworkers clearing roads buried by soil (Picture source from [[22]22]).).

33.. Analysis Analysis and and Discussion Discussion

3.1. Internal Internal Factors Factors:: Geographical Geographical Position Position,, Geological Geological Conditions Conditions and and Seismic Seismic Fracture Fracture Zone 3.1.1. Geographical Position and Geological Conditions 3.1.1. Geographical Position and Geological Conditions Ganluo is located in the Dadu River basin, belonging to the Yangtze River, which has a rapid, Ganluo is located in the Dadu River basin, belonging to the Yangtze River, which has a rapid, large flow and high drop. In addition, its valleys are narrow and steep [23]. The Niri River is a large flow and high drop. In addition, its valleys are narrow and steep [23]. The Niri River is a tributary of the middle reaches of the Dadu River. Its riverbed is deep, and the average reduction tributary of the middle reaches of the Dadu River. Its riverbed is deep, and the average reduction ratio of riverbed slope is 11 parts per thousand in Ganluo County [24]. Along the Niri River, there are ratio of riverbed slope is 11 parts per thousand in Ganluo County [24]. Along the Niri River, there many large alluvial cones and diluvial fans, gradually widening to the south of the river, a floodplain, are many large alluvial cones and diluvial fans, gradually widening to the south of the river, a and intermittently distributed terraces (see Figure6a). The valleys on both sides of the Niri River are floodplain, and intermittently distributed terraces (see Figure 6a). The valleys on both sides of the steep, with slopes of 40 to 70 (see Figure6b). The gradient of the slope has a great influence on the Niri River are steep, with◦ slopes◦ of 40° to 70° (see Figure 6b). The gradient of the slope has a great susceptibility to landslides. It is widely known that slope steepness is highly related to susceptibility influence on the susceptibility to landslides. It is widely known that slope steepness is highly related to rapid landslides. When the dip angle of rock strata is greater than 40 , the bedding layer commonly to susceptibility to rapid landslides. When the dip angle of rock strata is◦ greater than 40°, the bedding controls the slope surface, and it is difficult to form landslides. However, when the lithology of the layer commonly controls the slope surface, and it is difficult to form landslides. However, when the lower part of the slope body is weak or broken by tectonic action, the upper part of the slope body lithology of the lower part of the slope body is weak or broken by tectonic action, the upper part of may form landslides with the upper bedding and lower cutting layers and the action of the bedding the slope body may form landslides with the upper bedding and lower cutting layers and the action pushing force on the upper rock mass [25]. In addition to the above rock properties, the possibility of of the bedding pushing force on the upper rock mass [25]. In addition to the above rock properties, landslides and debris flow in the canyons on both sides of the riverbank is greatly increased due to the the possibility of landslides and debris flow in the canyons on both sides of the riverbank is greatly low vegetation coverage. increased due to the low vegetation coverage.

Geosciences 2019, 9, 497 6 of 12

Geosciences 2019, 9, x FOR PEER REVIEW 6 of 12

(a) (b) Ü Ü

图例 图例 glstep1Contour line VALUEElevation (m) glstep2 3,132 - 4,252 <值>Slope (°) 2,552 - 3,131 0 - 17 2,059 - 2,551 18 - 28 1,548 - 2,058 29 - 39 Figure 6. (a) Topographic mapping of Ganluo (black triangle: landslide site); (b) GIS slope Figure 6. (a) Topographic640 - 1,547 mapping of Ganluo (black triangle:40 - 84 landslide site); (b) GIS slope figure 0 figure5 10 (black20 triangle: landslide site). 0 5 10 20 (black triangle: landslidekm site). km

3.1.2. SeismicFigure Fracture 6. (a) Topographic Zone mapping of Ganluo (black triangle: landslide site); (b) GIS slope figure (black triangle: landslide site).

Sichuan is an earthquake-prone area, and there have been many strong earthquakes around the site historically.3.1.2. Seismic Especially Fracture inZone the western region of the site, the Wenchuan earthquake Ms 8.0 in 2008 and the LushanSichuan earthquake is an earthquake Ms 7.0-prone in 2013 area, bothand there occurred have been near many the strong site [ 26earthquake,27]. Thes around Sichuan–Yunnan the Plateau issite a historical transitionly. Especially zone between in the western the Qinghai–Tibetan region of the site, the Plateau Wenchuan and earthquake Sichuan Ms Basin 8.0 in (see 2008 Figure 7). and the Lushan earthquake Ms 7.0 in 2013 both occurred near the site [26,27]. The Sichuan–Yunnan Under the pressure of the northward movement of the Indian Plate, it has become one of the most Plateau is a transition zone between the Qinghai–Tibetan Plateau and Sichuan Basin (see Figure 7). seismicallyUnder active the regionspressure inof the northward world [28 ].movement These earthquakes of the Indian mayPlate, reduce it has become the strength one of the of themost soil–rocks at the siteseismically [27] so thatactive even regions the in latestthe world earthquake [28]. These (onearthquakes 29 July may 2019) redu recordedce the strength near of the the site soil– was only 3.3 magnituderocks at inthe July site [ to27] August so that even in 2019 the latest and earthquake which was (on 200 29 kmJuly away2019) recorded from the near site. the Thesite was earthquake was alsoonly a significant 3.3 magnitude cause in of July the to slide August [29 in–32 2019]. and which was 200 km away from the site. The earthquake was also a significant cause of the slide [29–32].

Sichuan-Yunnan Plateau Dadu River

Sichuan Basin

Niri River

Figure 7. Topographic mapping of Ganluo County (yellow triangle) from Google Earth (yellow Figure 7. Topographic mapping of Ganluo County (yellow triangle) from Google Earth (yellow triangle triangle shows the location of Ganluo). shows the location of Ganluo).

3.2. External Factors: Rainfall, Track Vibration and Flood Erosion

3.2.1. Rainfall Ganluo is located in a mountainous terrain in which the average annual rainfall is 880 mm [33]. The average rainfall in June, July and August were 202.7, 214.5 and 210.7 mm, respectively Geosciences 2019, 9, x FOR PEER REVIEW 7 of 12

3.2. External Factors: Rainfall, Track Vibration and Flood Erosion Geosciences 2019, 9, 497 7 of 12 3.2.1. Rainfall Ganluo is located in a mountainous terrain in which the average annual rainfall is 880 mm [33]. (see FigureThe average8a). Rainwater rainfall in June, was July considered and August as were the 202.7, direct 214.5 trigger and 210.7 in this mm, landslide. respectively From(see Figure 26 July to 14 August8a). Rainwater 2019, 20 was days considered of rainfall as the were direct recorded trigger inand this landslide. the maximum From 26 rainfall July to 14 was August 136.91 2019, mm on 3 August20 days (see of Figure rainfall8b) werewhich recorded caused and the maximu mudslidem rainfall on 4 August.was 136.91 It mm occurred on 3 August approximately (see Figure 70 m from where8b) which landslide caused Athe occurred. mudslide on Figure 4 August.2 shows It occurred the seriously approximately damaged 70 m vegetationfrom where onlandslide the surface of theGeosciences mountainsA occurred. 2019 Figure, and9, x FOR the 2 PEER shows soil REVIEW erosion.the seriously The damaged continuous vegetation heavy on rainfall the surface caused of the serious mountains soil7 ofand loss, 12 and the soil erosion. The continuous heavy rainfall caused serious soil loss, and the soil around the the soil around the landslide location became extremely unstable. In addition, prior to the landslide 3.2.landslide External location Factors: became Rainfall, extremely Track Vibration unstable. and FloodIn addition, Erosion prior to the landslide (14 August), the (14 August),rainfallthe was rainfall 24.13 and was 8.13 24.13 mm and on 13 8.13 and mm 14 August on 13 and 2019, 14 respectively August 2019, (see respectively Figure 8b). Abundant (see Figure 8b). Abundant3.2.1.precipitation precipitation Rainfall increases increases pore water pore pressure water pressurein the soils, in leading the soils, to the leading decrease to of the their decrease shear strength. of their shear strength.The The poorGanluo poor shear is shearlocated strength strength in caused a mountainous causedthe collapse the terrain collapseof the in rockwhich of mass. thethe averagerock mass. annual rainfall is 880 mm [33]. The average rainfall in June, July and August were 202.7, 214.5 and 210.7 mm, respectively (see Figure

8a). 300Rainwater was considered as the direct trigger35 in this landslide. From 26 July to 14 August 2019, (a) Data from (http://weather.sina.com.cn/ganluo) H-temperature 160 (b) Data from (https://weather.com/zh-CN/weather) 20 days of rainfall were recorded and the L-temperature maximum rainfall was 136.91 mm on 3 August (see Figure 30 250 Monthly Precipitation 140 136.91 8b) which caused the mudslide on 4 August. It occurred approximately 70 m from where Rainfalllandslide (mm) 25

) 120 A occurred.200 Figure 2 shows the seriously damaged vegetation on the surface of the mountains and ℃ ( the soil erosion. The continuous heavy rainfall 20caused 100serious soil loss, and the soil around the landslide150 location became extremely unstable. In addition, prior to the landslide (14 August), the 15 erature 80 rainfall was 24.13 and 8.13 mm on 13 and 14 Augustp 2019, respectively (see Figure 8b). Abundant 100 10 Tem 60 54.86 precipitation increases pore water pressure in the soils, leading to the decrease of 51.31their shear strength. 43.18 40 The poor50 shear strength caused the collapse of the5 rock mass. Cumulative daily rainfall (mm)

Average monthly precipitation (mm) 25.4 24.13

20 12.7 14.48 0 0 10.16 6.6 7.87 6.86 8.13 2.543.56 123456789101112 1.02 0 000 0 300 35 0 28 29 (a) Data from (http://weather.sina.com.cn/ganluoMonth ) H-temperature 160 26 27 30 31 1 2 3456789 10 11 12 13 14 15 JUL(b) Data from (https://weather.com/zh-CN/weather)AUG L-temperature 30 Date 250 Monthly Precipitation 140 136.91 (a) (b) Rainfall (mm) 25

) 120 200 ℃ Figure 8. (a) Average monthly rainfall, the highest( temperature (H temperature), and the lowest Figure 8. (a) Average monthly rainfall, the highest20 temperature100 (H temperature), and the lowest 150temperature (L temperature) in Ganluo; (b) daily rainfall in Ganluo prior to landslide A (red triangles

temperature (L temperature) in Ganluo; (b) daily rainfallerature in Ganluo prior to landslide A (red triangles 15 80 show the date of the landslides). p show100 the date of the landslides). Tem 60 54.86 10 51.31 43.18 40 3.2.2. Flood50 Erosion 5 Cumulative daily rainfall (mm)

Average monthly precipitation (mm) 25.4 24.13

20 12.7 14.48 0 0 10.16 6.6 7.87 6.86 8.13 The induced effect of flowing water was mainly reflected in the3.56 slope instability caused by the 123456789101112 1.02 2.54 0 0 000 0 Month 26 27 28 29 30 31 1 2 3456789 10 11 12 13 14 15 erosion of the foot of the slope by the flowing water. This wasJUL an importantAUG inducing factor for several landslides along the Niri River. During the period from 25 July to 15 AugustDate 2019, because of the (a) (b) continuous heavy rainfall and the channel dam caused by the landslide that happened on 30 July 2019 (see FigureFigure9), the 8. Niri (a) Average River levelmonthly rose rainfall, sharply the highest and significantly temperature (H weakened temperature), the and stability the lowest of the foot of the slope. temperature (L temperature) in Ganluo; (b) daily rainfall in Ganluo prior to landslide A (red triangles show the date of the landslides).

Figure 9. Flood and channel dam caused by the landslide at Aidai village on 30 July (picture source from [34]).

3.2.3. Human Activity

Figure 9. Flood and channel dam caused by the landslide at Aidai village on 30 July (picture source Figure 9. Flood and channel dam caused by the landslide at Aidai village on 30 July (picture source from [34]). from [34]). 3.2.3. Human Activity

Geosciences 2019, 9, 497 8 of 12

3.2.3. Human Activity The Chengdu–Kunming railway is the only railway connecting the southwest of China with the rest of the country. Considering the safety of the railway passengers in the rainy season and the demand for railway transportation for the economic development of this region, the EMD rushed to repair the railway line after the mudslide occurred on 4 August. After the railway line was repaired on 10 August, the railway authorities arranged this trial run of trains loaded with goods. At 12:44 on 14 August, shortly after a train passed the site at 12:40, the landslide occurred.

3.3. Recommendations The Chengdu–Kunming railway is the only railway connected to the southwest region. It is essential for the economic development of this region. The railroad navigates many steep, geologically complex valleys located in remote mountainous areas with no human presence to monitor geological conditions. Landslide risk analysis, pre-disaster early warning, and post-disaster reconstruction management are three significant points when encountering a natural disaster. Therefore, the following recommendations are given to reduce human casualties and property loss.

1. Risk assessment should be conducted to reveal the risk level along the Chengdu–Kunming railway. There are many quantitative or statistical risk assessment methods able to predict landslide susceptibility, e.g., logistic regression (LR) [35], analytical hierarchy process (AHP) [36–41], and frequency ratio (FR). The landslide susceptibility can also be mapped using geographic information system (GIS) technology [36–44]. Based on a comparative study, Yalcin [45] concluded that the AHP method yielded a more realistic scenario regarding the actual distribution of landslide susceptibility. The application of these models can give guidance for monitoring the occurrence of a landslide. 2. Therefore, the application of remote sensing (RS) and GIS for landslide disaster management is necessary [15]. For instance, two consecutive landslides within a month starting on 11 October 2018 and twice blocked the Jinsha River which is the upper reaches of the Yangtze River at the junction of Sichuan Province and Tibet in China [46]. However, with the deployment of a real-time landslide early warning system, local authorities took immediate action to quickly and safely construct spillways to drain the dammed lake. It avoided the most serious cases, where loss of life and property is at least one order of magnitude lower than that observed without rapid intervention. Because the western region of Sichuan is the transition zone of the Sichuan Basin and Yun-Gui Plateau and the geological characteristics of these two regions are similar, the railway and its related departments can follow this model for further research and development of monitoring. The government may be able to obtain all the data from the time-lapse to the end of a landslide by monitoring areas where landslides occur on a long-term basis such as the example above. In addition, drones can also periodically measure the topography of the landslide’s starting area, combined with GIS technology to analyse the time variation of the storage space distribution in the landslide’s starting area [36,38,47]. 3. In Ganluo County, Sichuan Province, the summer rainfall is rich, and the groundwater is abundant [31]. Most landslides are triggered by rainfall, with the influence of the monsoon climate and environmental changes. The hydro-meteorological data also show that two series of early precipitation for 10 days may produce excess pore water pressure and high saturation in landslide and debris flow areas [48]. Therefore, the data using the rainfall assimilation method provides a new method for merging multisource data with models, which may be used to predict the displacement of landslides [49]. In addition, the landslide simultaneous state and parameter estimation strategy were able to make use of time-series displacements and hydrological information for the joint estimation of landslide displacement and model parameters. It was able to improve the performance considerably. The establishment of a groundwater flow model may be effective for better planning and location of landslide stability enhancement Geosciences 2019, 9, 497 9 of 12

measures [50]. In addition to the methods mentioned above, relatively low-cost countermeasure could be employed to define rainfall thresholds that have been used as a base for an EWS in Emilia Romagna (Italy). Experiences show that only a few data are needed if a long-term research project is established, but the performance can improve greatly with time [51]. 4. The deaths and missing persons at the landslide site were station staff and workers who were clearing the railway drains. Therefore, in such a remote area, if the geological survey and landslide warning after the landslide occur, similar casualties could be avoided. In particular, after the first mudslide (19 July) and landslide (4 August), measures such as reinforcement, blasting, or removal of the surrounding loose soil should be taken quickly.

4. Concluding Remarks This article reports on the landslide that occurred on 14 August 2019 in Sichuan, China. After preliminary investigation and analysis, the following conclusions are drawn:

1. A moderate size landslide event, with about 48000 m3 of earth and rocks, occurred at Ganluo, resulting in 12 fatalities and five people reported as missing, destroying a section of the railway of approximately 70 m and causing this section of the train service to be suspended for 15 days. 2. The reason that caused the landslides were due to the combined effects of frequent former earthquakes, steep topography, large amounts of rainfall water, deep-seated sliding interface, dynamic train running load, and the effects of the previous two geological disasters, etc. These effects led to severe casualties and environmental impacts. For prevention and mitigation of these slide hazards, risk assessment concerning landslides should be conducted first to reveal the risk level along the Chengdu–Kunming railway line. Based on the risk assessment results, early warning systems should be provided through cost-effective precipitation and groundwater sensing technologies as well as the establishment of GIS databases to continuously monitor geologically risk-prone areas. 3. After the landslide disaster, continuous monitoring of the surrounding soil in a timely manner should be conducted to deploy and evacuate relevant rescue workers. Disaster prevention education for villagers living in vulnerable areas is also important. This will reduce casualties in similar incidents in the future.

Author Contributions: This paper represents the result of collaborative teamwork. S.-L.S. developed the concept; Q.Z. drafted the manuscript; A.-N.Z. and H.C. provided constructive suggestions and revised the manuscript. The four authors contributed equally to this work. Funding: This research was funded by the Research Funding of Shantou University for New Faculty (Grant No. NTF19024-2019). Acknowledgments: The authors would like to express sincere thanks to the anonymous reviewers and editors. Their constructive comments help the authors to improve the quality of the manuscript. Conflicts of Interest: The authors declare no conflict of interest.

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