"8·" Landslide in Shangjie Group, Matatun Village, Yanxia Township, Guiding County, Qiannan Prefecture, Guizhou

1 Overview of the landslide

The Shangjie Group in Matatun Village, Yanxia Township, Guiding County is located in the southeast direction of Guiding County, Qiannan Prefecture, Guizhou Province, about 5km away from Yanxia Township. The geographical coordinates are: 107°17'43″ east longitude, 26°23'11″ north latitude, and 1180m above sea level. On August 18, 2011, a landslide occurred in the Shangjie Formation of Matatun Village, Yanxia Township, Guiding County. It was about 300m long, 150m wide, 5-15m thick, with an average thickness of about 10m, and a volume of 450,000 m3. It was a medium-sized landslide. The landslide threatened the lives and property of three construction houses in the Shangjie Group, construction workers, the 110KV-036 high-voltage transmission line tower of the Jiugu Line, the S309 Highway, and the passing pedestrians and vehicles. Mainly because the villagers' houses were built close to the mountain and cut into the slope, and no protective measures were taken after cutting the slope. Since mid-August, the area has been hit by heavy rains for several consecutive days, leading to landslides. Due to timely and accurate early warning forecasts, rapid emergency response, effective organization, and measures in place, 40 people successfully escaped danger and no casualties or property losses were caused.

2 Basic environmental background

2.1 Topography

The landslide area is located in the southern part of the Guizhou Plateau and is dominated by valley basins and hilly landforms. The topography in the area is relatively undulating. Large, the highest altitude is 1502.5m, the lowest is 1142.6m, the maximum relative height difference is 359.9m, and the slope is 30°~50°.

2.2 Stratum Lithology

The karst landform is developed in the landslide area, and the exposed strata from new to old are Quaternary (Q) residual slope deposits containing sandy clay and sub-clay; The dolomite of the Yaosuo Formation (D3y) of the Upper Devonian System contains mud in the upper part and the top is limestone; the dolomite of the Wangchengpo Formation (D3w) of the Upper Devonian System is intercalated with a small amount of limestone; the Dushan Formation of the Middle Devonian System (D2d) Dolomite, limestone, quartz sandstone, and intercalated shale; medium to thick quartz sandstone in the Upper Bangzhai Formation of the Middle Devonian System (D2b).

2.3 Hydrogeology

According to the analysis of the lithology of the strata exposed in the landslide area and adjacent areas, the water-bearing medium and the dynamic conditions of groundwater, the main types of groundwater in the area include pure carbonate rock. There are three categories: karst water, clastic rock fissure water, and loose rock pore water. Groundwater is recharged by atmospheric precipitation, mainly through karst; carbonate rock karst water and bedrock fissure water are mainly recharged by infiltration and discharged in gullies or low-pressure areas cut by terrain.

2.4 Meteorology and Hydrology

The landslide area has a typical warm and humid monsoon climate in the mid-subtropics, with four distinct seasons, abundant heat, abundant rainfall, cloudiness and fog, small temperature difference, and mild climate. . The average temperature is 15℃, the average rainfall is 1100~1400mm, there is no severe cold in winter and no scorching heat in summer. The average temperature in the hottest month (July) is 24.3~28.3℃, and the average temperature difference is 15.1~17.3℃. The multi-year average rainfall is 1217.5mm, with an annual maximum of 1411.7mm and an annual minimum of 1158.3mm. The most important surface water system in the landslide area is the Gudi River, which runs from northeast to southwest and is located about 100m south of the landslide point. Other surface water systems are mostly seasonal streams and belong to the Wujiang River system in the Yangtze River Basin.

2.5 Human Engineering Activities

There are three households under construction near the landslide. The front edge is unreasonably cut, forming a high and steep slope. No effective treatment measures have been taken. The shear strength of rock and soil is significantly reduced, causing cracks in the mountain and leading to landslides after heavy rains.

Figure 1 Construction houses and high-voltage transmission towers threatened by landslides

Figure 2 Shear opening at the front edge of the landslide

3 Monitoring and emergency avoidance

3. 1 Monitoring and Early Warning

Guiding County has formulated a geological disaster inspection and monitoring system and implements the principle of "whoever is threatened is responsible for monitoring". The villagers of this group are responsible for daily inspection and monitoring of the hidden danger points. Observe the deformation and damage conditions of landslides and their macroscopic precursors, and record in detail the monitoring points, time, monitoring data and monitors of each inspection and monitoring. Monitors have stepped up monitoring after several days of heavy rain since mid-August. On August 15, monitoring personnel discovered that the foundations of houses under construction in the Shangjie Group of Matatun Village had cracks, and multiple cracks with a width of 3 to 10cm appeared on the ground. Shear displacement has occurred at the front edge of the landslide, and there is a danger of sliding down at any time. After the monitoring personnel discovered the danger, they immediately reported it to the Yanxia Township Land and Resources Office. After receiving the report, the Land and Resources Office immediately reported it to the Yanxia Township People's Government and the Guiding County Land and Resources Bureau. At the same time, it launched an early warning mechanism and issued a landslide early warning to residents of the Shangjie Group who were threatened by danger near the hidden danger point.

Figure 3 The trailing edge of the landslide collapsed

Figure 4 Plan of the 1:10,000 landslide

Figure 5 Topographic and geological map of the 1:50,000 landslide

3. 2 Emergency Evacuation

After receiving the report of the danger, the relevant leaders of the Guiding County Land and Resources Bureau and the Yanxia Township People’s Government immediately rushed to the scene and asked the street team 3 who were threatened by the landslide to The construction of the house was immediately stopped and nearby villagers were evacuated for proper resettlement. Danger areas are also demarcated, and protective fences and warning signs are set up in the areas to prevent people and animals from accidentally entering and causing casualties and property losses.

The landslide occurred on August 18. After receiving the disaster report, the Guizhou Provincial Geological and Environmental Monitoring Institute immediately organized professional and technical personnel to rush to Guiding County at noon on August 19, and together with the staff of the Guiding County Land and Resources Bureau, conducted emergency response to the disaster site. Investigate and take appropriate emergency measures.

4 Experience and Enlightenment

(1) Party committees and governments at all levels attach great importance to and deploy carefully, which is the prerequisite for the prevention and control of geological disasters.

At the beginning of the flood season, the Qiannan Prefecture Government organized various departments to hold consecutive emergency flood prevention meetings in response to a heavy rainfall, requiring all departments to carry out flood prevention and disaster prevention work in a timely manner. The Guiding County Party Committee and County Government conscientiously implemented the "four in place" system, laying a good foundation for emergency response to landslide disasters.

(2) The solid work of the land and resources departments and related departments is the key to the prevention and control of geological disasters.

First, the responsibility for disaster prevention is implemented at the grassroots level. Before the flood season, the Guiding County Bureau of Land and Resources assigned disaster prevention responsibilities at each hidden danger point to each person and signed responsibility letters layer by layer to form a mass detection and mass prevention system. Second, the basic work for disaster prevention is in place. Formulate practical emergency plans, resolutely implement the 24-hour duty system, and respond quickly to dangerous situations. Third, early warning and forecasting are timely and accurate. Accurate forecasts from the Guizhou Provincial Geological Environment Monitoring Institute and accurate early warnings from monitors are an important guarantee for successful avoidance this time.

(3) Mobilizing the masses to proactively prevent disasters is fundamental to the prevention and control of geological disasters.

First, promote disaster prevention knowledge. From March to May, Guiding County carried out touring publicity and training activities on rural geological disaster prevention and control knowledge in twelve counties and cities in Qiannan Prefecture, and widely publicized geological disasters through various forms such as distributing promotional materials, posting pictures, playing promotional videos, and on-site explanations. Prevention and control knowledge has made disaster prevention knowledge widely popularized. The second is to conduct emergency avoidance drills. Before the disaster, the Guiding County Land and Resources Department organized a geological disaster emergency avoidance drill in nearby towns and villages, which improved the people's disaster prevention awareness and emergency avoidance capabilities, which played a vital role in the successful avoidance of this disaster.

(The basic information for this section is provided by the Department of Land and Resources of Guizhou Province and the editor-in-chief is Chu Hongliang)