1 Basic situation
At around 3 a.m. on June 26, 2011, a landslide geological disaster occurred in the Xiaodongou Mining Area, Baiyuli, Xingao Township, Dai County, Shanxi Province. The landslide body is about 290m long and 60m wide, and the volume of soil and rocks slid out of the slide bed exceeds 6000m3. The sliding earth and rocks buried the temporary migrant workers' houses down the slope, causing 9 deaths and 4 injuries to the migrant workers.
2 Analysis of regional geological environment and genetic trends
2. 1 Regional geological environment conditions
Dai County has a temperate semi-arid climate. According to the meteorology of Wuli Village in Dai County According to the station data, the average annual rainfall is 430. 6mm, the average annual evaporation is 1770. 4mm, and the relative humidity is 56%. The maximum monthly rainfall is 330. 5mm, and the maximum daily rainfall is 100. 4mm.
This area is located in the bedrock mountainous area of ??the western section of Wutai Mountain. The terrain is high and undulating, with strong terrain cutting and relatively developed gullies. It is a typical bedrock erosion landform. The highest elevation in the mining area is 1,700m, the lowest elevation is 1,400m, and the maximum relative height difference is 300m. It belongs to a medium-low mountainous area.
The strata in this area are the metamorphic rock series of the Jingangku Formation of the Shizui Group of the Archaean Wutai Super Group. The original rock is a set of clay-clastic rocks deposited from the continental margin to the coast. After multi-stage regional metamorphism and thermal action, a set of low- and medium-grade regional metamorphic rock series was formed. The lithology is mainly composed of various types of schist.
This area is located at the eastern end of the Baiyuli syncline structure at the outer edge of the regional Taihuai Group's double-fold and syncline. The main structure in the mining area is the Baiyuli inverted tilt, with the north wing inverted to the southeast. The inverted tilted hub moves northeast-northeast, undulating, with the northeast end rising to a high amplitude and the south-west end slightly upturning.
Within the mining area, there are no river valleys with perennial water flow. Each valley is a temporary flood drainage channel after heavy rains in summer, and is usually a dry ditch. This area belongs to a mountainous area fed by metamorphic rock bedrock in the regional hydrogeological unit, and the main stratigraphic lithology in the area is metamorphic rock. Atmospheric precipitation is the main supply source of groundwater in this area. The water richness of each aquifer is poor, and the groundwater level is deeply buried.
2. 2 Landslide geological hazard characteristics
The landslide is developed on the ridge on the southwest side of Xiaodong Valley in Baiyu. The upper part is bounded by the gully, and the upper part is edged by the landslide scarp, sliding towards the Xiaodonggou ravine in the northeast direction. The landslide body is horseshoe-shaped on the plane and distributed irregularly. The landslide body is about 290m long in the southwest-northeast direction and about 60m wide in the northwest-southeast direction. The average thickness of the landslide body is about 3m, and the height difference between the front and rear edges is about 140m. According to on-site observations, the landslide body is mainly composed of residual slope deposits and highly weathered rock formations. The volume of the landslide is about 50,000 m3, and the volume of earth and rock that slides out of the slide bed is about 6,000 m3. It is a small landslide. The topography of the landslide area, landslide scarps, cracks and other characteristics are detailed in Figures 1 and 2.
Figure 1 Landslide site
Figure 2 The cliff at the top of the landslide
2. 3 Disaster and danger trends
The landslide is a natural disaster. A landslide caused the earth and rocks that fell from the upper part of the slope to slide down the slope, destroying 10 temporary houses buried at the bottom of the slope, causing 9 deaths and 4 injuries.
At present, the disaster point is still in the unstable deformation stage, and it is the local rainy season. Under certain inducements, sliding will still occur, directly threatening the safety of rescue and disaster relief personnel.
Figure 3 Local terrain slope of landslide area
3 Analysis of causes of landslide geological hazards
3. 1 Topographic and geological factors
This area is The landform of mountainous valleys and mountain ridge slopes. The terrain slope in the landslide area is steep, with a terrain slope of 30° to 45°. The rock layers are mainly composed of various types of schists. The shallow residual slopes have thicker loose accumulations and strongly weathered rock layers, and the geotechnical properties are loose. , the shear strength is low, and it has the basic conditions for landslides.
3. 2 Atmospheric precipitation factors
Before this geological disaster occurred, there was heavy rainfall in the area. On the one hand, heavy rainfall directly increases the weight of the rock and soil mass and increases the sliding component; on the other hand, rainfall infiltration changes the physical and mechanical properties of the loose layer, reduces the internal friction of the loose medium, and reduces the rock The anti-skid ability of the soil layer.
Analysis shows that the steep terrain slope of the landslide area, thick residual slope sediments and strongly weathered rock layers accumulated in the shallow part are the basic conditions for the occurrence of this landslide, and heavy rainfall is the main inducing factor leading to the occurrence of this landslide.
4 Geological disaster emergency prevention and control
4. 1 Emergency response and rescue and disaster relief
At around 3 a.m. on June 26, Baiyuli, Xingao Township, Dai County After the landslide geological disaster occurred in the Xiaodonggou mining area, Xinzhou City immediately launched the Level III emergency plan for sudden geological disasters, established the "6·26" accident rescue headquarters, and mobilized land and safety supervision technicians, public security officers, and explosion prevention team members. and other teams to form emergency medical rescue and emergency response teams to carry out emergency rescue and disaster relief work.
4. 2 Emergency Response
After the June 26 accident, the Shanxi Provincial Party Committee and Provincial Government attached great importance to it, and relevant departments such as the Provincial Emergency Office, the Provincial Department of Land and Resources, and the Provincial Work Safety Supervision Bureau rushed to Direct rescue on site. The specific emergency response measures taken are: ① After investigation and verification, the number of casualties has been determined and all buried persons have been found. ②Delimit the danger zone, set up a warning line around the entire landslide, and prohibit idlers from entering the danger zone. ③ Strengthen monitoring, set up observation points at different parts of the landslide body, conduct 24-hour uninterrupted deformation monitoring and keep records. ④ Evacuate all personnel and equipment downstream of the landslide ravine to prevent secondary geological disasters. ⑤ It is recommended to entrust units with corresponding qualifications to conduct detailed survey, design and treatment of landslides and other related work.
5 Experience and Enlightenment
The occurrence of the “6·26” landslide disaster caused heavy losses, great impact, and profound lessons, and brought the following enlightenment:
We must change our mindset and adhere to the concept of people-oriented and safe development. Properly resettle and improve the living conditions of migrant workers.
The city immediately carried out a large-scale investigation of geological disaster hazards to identify various geological disaster hazards, and demolished all temporary work sheds set up by all enterprises in unsafe areas to effectively prevent the occurrence of similar geological disasters.
It is necessary to conduct study and training for relevant personnel, vigorously publicize the knowledge of geological disaster prevention and control, improve the awareness of disaster prevention and avoidance of relevant personnel, and enhance the people's self-rescue and mutual rescue capabilities.
After the occurrence of this geological disaster, the emergency rescue was timely, the emergency response was orderly, and the measures taken were effective. Thanks to the timely activation of the emergency plan, the development of the situation and the occurrence of secondary disasters were effectively controlled.
(The basic information for this section is provided by the Shanxi Provincial Department of Land and Resources, editor-in-chief Wei Yunjie)