"8" Yutian Formation Landslide in Wengduo Village, Nanlong Township, Kaiyang County, Guizhou Province

On August 20th, 20 13, affected by continuous heavy rainfall, two landslides occurred in Yutian Formation, Wengduo Village, Nanlong Township, Kaiyang County, Guiyang City, which caused damage to many houses, cultivated land and roads in this area, including 6 households with 28 people, but no casualties were caused. The geographical coordinates of the disaster site are 107 04' 49.3 "east longitude and 27 0 1' 15.5" north latitude.

2 Geological hazard characteristics

2. 1 Regional geological environment conditions

2. 1. 1 meteorology and hydrology

The disaster area belongs to the humid and mild climate zone in the middle subtropical zone, with mild and suitable climate, no severe cold in winter, no heat in summer, and wet and rainy. Disastrous weather includes summer drought, late spring cold, summer drought, heavy rain, hail, continuous autumn rain and freezing. Annual average temperature 13.3℃, extreme maximum temperature 33.7℃, minimum temperature -7.7℃. The annual average precipitation 10 19.4 mm, with rainy season from May to September and dry season from 165438+ 10. It belongs to the Wujiang River system in the Yangtze River basin, with a north-west gully, and the flow during the investigation period is about1.5l/s.

2. 1.2 Terrain

The survey area is gully landform of eroded hillside. The gully extends to the northwest, and the terrain in the area is undulating. The overall terrain is high on both sides and low in the middle, with an altitude of 780 ~ 105438+06.438+0m and a relative height difference of 236.38+0m ... Landslide geological disasters develop in the middle and lower part of the left bank slope of Xigou. The natural slope is about 30, the residual slope on the slope is 0 ~ 5m thick, and the trees and shrubs are flourishing. The residents of Yutian Formation live scattered on the landslide.

2. 1.3 Formation lithology

The strata exposed from new to old in this area are:

(1) Quaternary residual (QEL+DL): the lithology is gravel soil, with gravel content more than 50%. The lithology of gravel is mainly mudstone and argillaceous dolomite, and the lithology of gravel is limestone, with gravel fragmentation of 0.1m× 0./kloc-0.

(2) The lithology of Lower Cambrian Qingxudong Fm is mainly gray and dark gray medium-thick massive limestone, and the rock mass integrity is good. The thickness of this layer is 150 ~ 400 m, which belongs to hard rock engineering geological rock group.

(3) The lithology of Jindingshan Formation in Lower Cambrian is mainly grayish yellow shale and purplish red calcareous mudstone, and the rock mass is broken. This layer is100 ~ 250m thick and belongs to soft rock engineering geological rock formation.

(4) The lithology of Niutitang Formation in Lower Cambrian is mainly black carbonaceous shale mixed with gray green sandy shale, and the rock mass is broken. This layer is100 ~ 200m thick and belongs to soft rock engineering geological rock formation.

2. 1.4 Hydrogeological conditions

According to the stratum lithology, groundwater dynamic conditions and water-bearing medium characteristics exposed in the area, the groundwater types in the survey area are divided into loose rock pore water, carbonate karst water and bedrock fissure water. Among them, loose rock pore water exists in the pores of residual slope gravel soil, and its water abundance is weak; Karst water occurs in caves and fractures of limestone in Qingxudong, Lower Cambrian, with medium water abundance. Bedrock fissure water occurs in weathering fissures of Jindingshan Formation and Niutitang Formation of Lower Cambrian, and its water abundance is poor.

Groundwater in the survey area is mainly replenished by atmospheric precipitation, which seeps into groundwater through cracks. After receiving recharge, groundwater flows from west to east and is discharged into low-lying areas in the form of springs. Three descending springs are exposed in the survey area.

2. 1.5 geological structure and earthquake

The geological structure of the survey area is complex, and two faults with unknown properties are developed: ① strike is about 70, length is about 2.5km, and the affected width is about 300 m; ② The strike is about 35, the length is about 1.5km, and the affected width is about100m; The two faults intersect in the middle and lower part of the left bank slope of Xigou. Affected by faults, joints and fissures are extremely developed. The occurrence of the two main control fractures are 250 ∠ 75 and 70 ∠ 60 respectively, with the fracture width of 1 ~ 5 cm and the fracture spacing of 0. 1 ~ 0.5 m, and the rock mass is partially penetrated, with poor integrity.

According to the Seismic Parameter Zoning Map of China issued by the State Bureau of Quality and Technical Supervision (GB 18306—200 1), the basic earthquake intensity in the working area is VI, and the crust is stable.

2.2 Disaster characteristics and scope of influence

2.2. 1 disaster characteristics

Of the two landslide disasters, 1 is located on the left bank of the gully upstream, and No.2 is located on the left bank of the gully downstream (Figure 1).

Characteristics of landslide 1: 1 is a residual slope nappe landslide with an original slope of 45 and a back slope of about 30. The elevation of the landslide shear outlet is 776m, and the elevation of the rear edge is 885m m. The landslide is tongue-shaped, with a longitudinal length of about 300 meters and a lateral width of about 200 meters, with an average thickness of 5 meters and a total volume of about 300,000 cubic meters. The main sliding direction of the landslide is 45, and the sliding control structure surface is the rock-soil contact surface. The main component of the sliding body is clay mixed with gravel, with gravel content of about 50% and loose structure.

At present, the characteristics of the landslide are obvious, which are embodied in the following two aspects.

(1) tensile crack

A tensile crack is developed at the trailing edge of the landslide, which is arc-shaped, about 60m long and about 10cm wide, and filled with gravel soil. According to the local villagers, the crack first appeared in June of 20 10, and it tends to widen year by year.

Figure 1 Landslide disaster panorama

(2) Local landslide

After the rainstorm on May 25th, 20 13, four small-scale landslides occurred in this landslide:

① Located in the farmland on the right side of the upper part of the landslide, the landslide range is about 25m long and 40m wide, and the sliding direction is 0. A staggered ridge with a height of 0.2 meters is formed near the top of the slope.

② It is located under the middle dirt road in the middle and upper part of the landslide, with a landslide range of about 12m, a width of about 10m and a sliding direction of 45, forming a staggered ridge with a height of about1.5m..

③ Behind Nie Shaofu's house on the right side of the lower part of the landslide, the landslide range is about 5m long and 30m wide, the sliding direction is 20, and the sliding distance is 5m, causing a reservoir to move forward 5m, and the pillars of the house are partially buried.

④ It is located under the cement road on the left side in the middle of the landslide. The landslide range is about 13m, the width is about 10m, and the sliding direction is 90, causing a fir tree to slip 5m, forming a staggered ridge with a height of about 2.5m.

Characteristics of No.2 landslide disaster: No.2 landslide is a residual slope type landslide, with an original slope of 45 and a slope of about 30. The elevation of the landslide shear outlet is 700m, and the elevation of the rear edge is 8 10m. The plane shape of the landslide is nearly rectangular, with a longitudinal length of about 300 meters and a lateral width of about 300 meters. The average thickness of the landslide is 3m, and the total volume is about 270,000m3. The main sliding direction of the landslide is 30, and the sliding control structure surface is the rock-soil contact surface. The main component of the sliding body is clay mixed with gravel, and the gravel content is about 75%. Gravel is limestone falling from the top of the slope with loose structure.

The characteristics of this landslide are obvious, which are embodied in the following two aspects:

(1) tensile crack. There are three tension cracks on the left side of the middle and upper part of the landslide. A long crack appeared in the yard of Li Guoping, a villager, with a strike of 120, a length of 3m and a width of about 2cm. According to local villagers, the crack first appeared in June of 20 1 1 year, and it tends to widen year by year. The second crack developed in the yard of Liu Bingbing, a villager, and it was long, with the strike of 130, the length of 6m and the width of 0.5 ~ 1cm. According to local villagers, the cracks first appeared in 20 12 1 month, and there is a trend of expanding year by year. The third crack appeared on the wall of villager Liu Bingbing's house, and the building structure was brick-concrete structure. The fourth fracture is long, with the occurrence of 230 ∠ 20, the length of 1.5m and the width of 0.5 ~1.5m.. According to local villagers, the cracks first appeared in 20 12 1 month, and there is a trend of expanding year by year.

Figure 2/Characteristics of LandslideNo. KLOC-0/

(2) Local slump. There was a landslide 20 years ago, and after the rainstorm on May 25, 20 13, there were three small-scale landslides:

① Located in the farmland above the cement road in the middle and upper part of the landslide, the landslide range is about 15m long and 10m wide, and the sliding direction is 0, forming a staggered ridge with a height of 3m near the top of the slope.

(2) Behind the residential building on the right side of the middle and upper part of the landslide, the landslide range is about 15m long, about 10m wide, and the sliding direction is 40, forming a staggered ridge with a height of about 2.5m, which is the main point of this disaster.

③ It is located under the cement road on the right side of the middle and upper part of the landslide. The sliding range is about 3m long and 2m wide, and the sliding direction is 320, which makes the cement road half suspended.

2.2.2 Scope of influence

The landslide 1 directly threatens the life and property traffic safety of Yutian Formation and Tiedingshan Formation on the hillside with 52 people from 9 households and 260m of rural roads, while the landslide # 2 directly threatens the life and property traffic safety of Yutian Formation 1 1 households with 63 people and 240m of rural roads on the hillside. To sum up, this landslide disaster has affected 20 households 1 13 people and 500 meters of rural roads.

Under the influence of special climate or engineering activities, if the landslide declines as a whole, it will pose a serious threat to 20 households 1 13 people in the dangerous area; Once the landslide slides locally, it will do harm to pedestrians and houses on the slope.

Figure 3 Characteristics of No.2 Landslide Disaster

Cause of disaster

Landslides 1 and No.2 are located on straight steep slopes, and the area belongs to the stratum combination type of "upper hard and lower soft", with thick residual slope, loose structure and strong water permeability and saturation. When it rains, the rain seeps into the residual slope deposit, which makes the sliding zone soil saturated and softened. On sunny days, the water level drops sharply. Under the combined action of internal pore water pressure, groundwater dynamics and soil weight, the soil at the rear edge soaked by water will deform, slide towards the empty surface of the valley and push down the slope.

3. Geological hazard inspection and monitoring

The landslide in Wengduo Village, Nanlong Township used to be a hidden danger point of geological disasters. Because it is monitored by Shuangliu Town Land Institute of Kaiyang County Land and Resources Bureau for a long time, it is inspected once a week at ordinary times, and the inspection density is strengthened when it rains, and the monitoring records are made to record the deformation of geological disasters in detail.

After the dangerous situation occurs, start the plan in time and implement emergency hedging. The Land and Resources Bureau of Kaiyang County and the People's Government of Nanlong Township immediately decided to start the plan, organized relevant personnel to rush to the scene of the phenomenon, set up warning lines and warning signs, demarcate dangerous areas, and organize the people to evacuate to safety.

4 Experience and Enlightenment

(1) patrol inspection should be in place and respond quickly. Focus on the hidden danger points of geological disasters, schools, towns, villages and other densely populated areas for detailed investigation to ensure that there are no omissions, no blind spots and no dead ends. This is the key to effectively deal with emergencies, especially for the emergency treatment of landslides and collapses. Because the collapse point is behind the village, the mountain is steep and covered with trees, it is difficult to monitor and find cracks in dangerous rock mass in detail. If the patrol inspection is not in place and the government department does not respond quickly, it may delay the best opportunity for evacuation and rescue.

(2) Establish and improve the emergency management system to ensure nip in the bud. We have established a perfect monitoring, early warning and forecasting system for group monitoring and prevention, a system for pre-flood investigation of geological disasters, a system for inspection in flood season and a system for post-flood review, a system for quick disaster reporting and a system for duty in flood season. Once a geological disaster occurs, we will immediately start the emergency plan. When the danger showed signs of collapse, the county land and resources bureau and the township government immediately reported it to the county party Committee and the county government, which bought time for the safe evacuation of personnel and set up an emergency evacuation leading group in time to deal with the emergency situation. Party member cadres in counties, townships and villages made preparations, and all of them devoted themselves to the rescue work that night, laying a solid foundation for the timely evacuation of people in dangerous areas.

(3) Emergency investigation and scientific disaster prevention. In order to truly understand the harm degree and development trend of potential collapse disasters, experts in geological disaster prevention and control were invited to carry out professional investigation in time, and a new model of professional technical support for geological disaster prevention and control at county level was established, which greatly promoted the emergency response of sudden geological disasters, and fed back the monitoring and prevention measures of experts to the county and township (town) people's governments, which improved the pertinence of geological disaster prevention and control and enhanced the professional and scientific management level of geological disaster prevention and control.

(4) Doing a good job in propaganda and training of geological disasters is the premise of successful hedging. Regular publicity and training on geological disasters can enhance people's awareness of active disaster prevention and enhance their ability of self-help and mutual rescue in group monitoring and prevention. In recent years, the county land and resources bureau has organized township leaders, village cadres and squad leaders. Carry out geological disaster prevention knowledge training before the flood season every year, teach basic knowledge such as simple monitoring of geological disasters, emergency disposal and emergency avoidance to grassroots cadres and masses, and enhance the awareness of disaster prevention of all threatened people. In the process of emergency evacuation, the threatened people can evacuate the dangerous area in the shortest time, which has won valuable time for successful evacuation. This is due to the effect of popularizing disaster prevention knowledge, the mutual assistance and cooperation of the people, and the people's awareness of disaster prevention and avoidance and self-help and mutual assistance.