The "8" landslide disaster in Yinjiang Bay, Gulin County, Luzhou City, Sichuan Province

2014 At 5: 30 am on August 8/KLOC-0, a massive landslide occurred in Yinjiang Bay, Jiushe, Shunhe Village, Longshan Town, Gulin County, Luzhou City, Sichuan Province, causing 29 houses to collapse, roads to be interrupted and land to be destroyed. Due to timely pre-disaster warning and effective measures of early avoidance and active avoidance, there were no casualties among 42 people in 1 1 household.

2 Geological hazard characteristics

2. 1 Regional geological environment conditions

2. 1. 1 meteorological conditions

Gulin County belongs to the transitional monsoon climate zone between subtropical zone and warm temperate zone, with distinct seasons and mild climate. The relative height difference in the region is large. Under the comprehensive influence of solar radiation, atmospheric circulation and landform types, the vertical difference of regional climate is large and the three-dimensional climate is remarkable. Rainfall in this area is mostly concentrated from May to August, accounting for about 65% of the annual rainfall.

2. 1.2 Terrain

The survey area is located in the south of Sichuan Basin, and the landform generally belongs to the slope landform of low mountainous area. The terrain in this area is generally characterized by low in the north and high in the south. The elevation of the landslide area is about 832 ~ 872 m, and the relative height difference is about 40 m. The upper part of the landslide on the south side of this area is steep, while the lower part is slightly gentle, and the terrain slope is about15 ~ 30. Below the landslide is a farming platform, and the front edge of the platform is a river ditch formed by gently inclined cutting; Landslide slopes are mostly forest land and cultivated land, with lush vegetation, farmers' houses on the slopes, and the top of the slopes is close to rural roads.

2. 1.3 Formation lithology

The overlying soil in the survey area is mainly Quaternary gravel soil, which is presumed to be an old landslide accumulation with a large thickness. Quaternary silty clay with different thickness is distributed locally around the landslide area. The underlying bedrock is mainly limestone of Permian Qixia Formation, sandy mudstone and shale of Liangshan Formation, and no bedrock is exposed within the landslide range.

2. 1.4 geological structure

Regionally, this area belongs to the Daloushan fold structural belt in the Yunnan-Guizhou-Sichuan-Hubei depression of the Yangtze paraplatform, which is located between the radial structural belts of Sichuan-Yunnan and Sichuan-Guizhou, with extremely developed faults and folds. The exposed strata are limestone of Permian Qixia Formation, sandy mudstone and shale of Liangshan Formation, and the rock occurrence is about 335 ~ 348 ∠ 18 ~ 30. The basic earthquake intensity in Gulin County is ⅵ, and the seismic activity in this area is weak, causing slight damage.

2. 1.5 Hydrogeological conditions

There is a gully at the front of the landslide in the survey area (below the main sliding direction). The running water in the gully is seasonal, and the surface water on the slope is mainly gully water formed by surface runoff and precipitation. Surface runoff mainly flows into the landslide area from the steep slopes and trailing edges on both sides, and the atmospheric precipitation in the gully and on the slope surface flows into the river ditch developed in the depression in front of the slope along the terrain. Rivers and ditches are perennial running water with an average flow of about 0.52m3/s, which erodes the soil in front of the slope all the year round. In addition, some survey areas are paddy fields.

Groundwater in the area is mainly upper stagnant water and pore water, which is replenished by atmospheric precipitation and surface water. Upper stagnant water occurs in gravel soil and silty clay, pore water occurs in loose gravel soil, strongly weathered sandy mudstone and shale, and fissure water mainly occurs in bedrock cracks.

2.2 Geological hazard characteristics

2.2. 1 Characteristics of disaster bodies

Landslide is located in No.9 community, Shunhe Village, Longshan Town, Gulin County. There was a landslide in the 1990s. 20 14, 1 8 On the morning of June 20th, under the continuous heavy rainfall, the Yinjiangwan landslide occurred again on a large scale (photo1). The rear edge of the new landslide is located in the southwest side of the slope, with an elevation of 857 ~ 872 m, and a through arc crack with a length of about 100m is formed at the rear edge of the landslide, and the soil is displaced by 2 ~100 m; The shear outlet of the landslide front is located at the gully in the middle and lower part of the slope (northeast side) and has been covered by the upper sliding zone soil; Parallel tensile cracks can be seen on both sides of the landslide, with a width of 1 ~ 7 cm and local penetration; The horizontal width of the landslide area is about 100m, the vertical length is about 250m, and the thickness of the landslide body is 2 ~10m. The landslide volume is about 65438+500,000 m3, and the main sliding direction of the landslide is about 25. The landslide is a small old soil landslide, and its sliding form is nappe type, and the parts with strong deformation are mainly concentrated in the middle and rear part of the landslide (photo 2).

Photo 1 Panorama of Yinjiangwan Landslide in Gulin County

Fig. 2 Strong failure area in the middle and rear part of landslide

2.2.2 Preliminary analysis and evaluation of disaster causes

Preliminary analysis on the genetic mechanism of (1) landslide

The slope terrain in the survey area is steep, and the shallow Quaternary on the slope is mainly gravel soil accumulated by thick old landslides, which is the internal cause of landslide formation, and the surface water erosion and infiltration formed by continuous heavy rainfall is the main external cause. The infiltration of surface water increases the weight of landslide and reduces the shear strength of structural plane. Sliding soil slides along the weak structural plane inside the accumulation layer under the action of gravity, resulting in landslide. The main factors affecting the formation of landslides include:

First, terrain and surface water factors. The terrain at the landslide is steep; The overlying Quaternary is an old landslide gravel soil accumulation, with loose stratum structure and poor mechanical properties. When there is continuous heavy rainfall, surface runoff is formed on the slope, and surface water permeates into the sliding body all the way to the foundation covering interface, which reduces the shear strength of the sliding surface (belt), increases the weight of the sliding body, changes the internal structural state of the soil, and thus reduces the stability of the landslide.

The second is the class factor. Landslides are mainly composed of gravel soil accumulated from Quaternary ancient landslides. The stratum structure is loose, and the soil composition is mainly silty clay, which is easy to deform and destroy under the action of external forces such as groundwater, and local soil is easy to soften after long-term soaking.

(2) landslide analysis and evaluation

According to field investigation, this landslide occurred during the continuous heavy rainfall in the rainy season this year. The landslide is the resurrection of an old landslide, and the slope where the landslide is located has local peristalsis before, and its stability is average. At present, the landslide has no obvious signs of new deformation or continuous sliding, but there are still creeping deformation in some areas. Because the landslide is an old landslide accumulation body, the accumulated gravel soil is thick, and it is possible to slide again in the case of continuous rainfall or rainstorm.

At the same time, on the slope on the right side outside the landslide area (on the right side of the gully below the landslide), near the river ditch below it, the slope is steep, the soil layer is thick, and landslides occur locally, with tens of meters of tensile cracks visible, and the soil body is staggered by about 0.3m m. There are two adobe houses in the middle of the slope, and cracks can also be seen on the dam wall, indicating that the landslide may develop in this direction. If the landslide below continues to develop, it will have a certain impact on the two households on the slope.

2.3 Disasters and dangers

At 5: 30 am on August 18, a landslide occurred in Yinjiang Bay, Jiushe, Shunhe Village, Longshan Town, causing 29 houses to collapse, road interruption, land damage 1 mu, and direct economic losses of more than 5 million yuan.

3 Geological hazards cause analysis and trend judgment

3. Cause analysis of1

(1) The cutting landform is developed, and the height difference between the front and rear edges of the landslide is large. The area where this point is located belongs to the slope landform of low mountain area, with a farming platform below the landslide and a river at the front edge of the platform, which is a cutting valley landform; There is a small gully under the landslide, and most of the slopes are woodland and cultivated land, with lush vegetation, and the top of the slope is close to the country road. The height difference between the front and rear edges of the landslide is nearly 50m, and the terrain slope is about15 ~ 30.

(2) The formation lithology is complex. The landslide area is presumed to be a landslide accumulation body, mainly gravel soil with a large thickness. Silty clay with different thickness is distributed locally around the landslide. The underlying bedrock is limestone of Permian Qixia Formation, sandstone mudstone and shale of Liangshan Formation, and no bedrock is exposed in the landslide area.

(3) Abundant surface water. There is a gully at the front of the landslide, and the flowing water in the gully is seasonal. In the rainy season, a small amount of rainwater on the slope penetrates into the ground through the pore cracks in the geotechnical layer, and the atmospheric precipitation in the gully flows into the river valley below, which exists all the year round, with a height difference of nearly 40m from the landslide.

(4) Adequate groundwater. Groundwater in the area is mainly stagnant water, pore water and fissure water, which is replenished by atmospheric precipitation and surface water. Upper stagnant water occurs in gravel soil and silty clay, pore water occurs in gravel soil, strongly weathered sandy mudstone and shale, and fissure water mainly occurs in bedrock cracks. Hydrogeological conditions are generally simple, and heavy rainfall is easy to make soil water saturated and unstable. If it encounters heavy rainfall again, it will easily lead to landslide sliding and cause harm.

3.2 Trend judgment

Below the main sliding direction of landslide (on the right side of slope) is gully. The gully is full of gravel soil sliding down from the landslide above, and debris flow is formed in the gully. A large number of soil inclusions carry vegetation and crops on both sides of the gully to the lower gully, which has a certain blocking effect on the gully. At present, the soil above the gully tends to be basically stable and has not slipped down. Comprehensive judgment shows that it is unlikely that debris flow will completely block the river and form a dammed lake.

4. Emergency prevention and control of geological disasters

4. 1 Emergency Response and Emergency Rescue

Monitor and Guo measure and record the identified hidden danger monitoring points every morning, noon and evening. On rainy days, in addition to monitoring before, during and after the rain, they are also on duty 24 hours a day. August, 2065438 16, 2065438, after receiving the information from the geological disaster early warning platform of Gulin County Land and Resources Bureau, the monitor immediately conveyed the rain information to the threatened farmers at the monitoring point. On August 17, there was a general rainstorm in Luzhou City, and the maximum rainfall in Gulin County was Yongle Town 174.6mm, and Longshan Town was 65434.6 mm In the early morning of August 18 1: 30, the monitor Wang Junshu inspected the hidden danger points and found that the front edge of the landslide was deformed, cracked and collapsed, and the monitoring points changed obviously. He predicted that the disaster might happen, and then used a semiconductor megaphone to call farmers to evacuate quickly according to the evacuation route of the geological disaster prevention plan, and gathered at the dam of Guo Dengshujia, an oriental villager who went up and down the fields along the landslide, and counted and checked the responsible contacts one by one to quickly help the elderly. At 2: 00 a.m., all 65 people from the hidden danger point 15 households have been evacuated. At the same time, another monitor, Guo, immediately reported this major danger to Shunhe Village Committee, Longshan Town Government and Land Emergency Department, and the town launched an emergency plan. At 3: 00 a.m.10, Shunhe villagers, Longshan town government, police station and land office staff rushed to the scene to support evacuation and avoidance.

4.2 Emergency treatment

After receiving the report of major danger, Shunhe Village Committee and Longshan Town Government immediately launched disaster prevention personnel and rushed to the scene at the first time to carry out evacuation, emergency rescue, resettlement of the affected people and on-site vigilance. Wan Qilong, deputy mayor, conducted on-the-spot command, implemented the division of labor between the squad leader, Guo, the village head, Chen Zuping of the National Land Office and the police station, and blocked four field paths and 1 tractor road entering the landslide to prevent villagers from evacuating.

After the disaster occurred, the municipal and county land and resources departments organized professional and technical personnel and geological prospecting units stationed in Luzhou to rush to the scene to carry out the work of delineating dangerous areas of geological disasters, strengthening inspections, investigating and monitoring, preventing secondary disasters, etc., and initially selected the post-disaster reconstruction housing address. Gulin county government led relevant departments to rush to the scene to direct rescue and disaster relief, properly resettle the affected people, ensure that the affected people have food, water, clothing, shelter and medical care, and send disaster relief materials such as cooking oil, rice, clothes and medicines. At the same time, the post-disaster reconstruction plan and relocation and avoidance subsidies were determined, and the affected people were comforted, emotionally stable and full of confidence in post-disaster reconstruction. After four months' efforts, the main body of newly-built housing for 26 families affected by the disaster has been basically completed, and most families can move into their new homes before the Spring Festival.

5 Experience and Enlightenment

(1) Party committees and governments at all levels and disaster prevention departments attach great importance to it. The Sichuan Provincial Party Committee and the provincial government attach great importance to the prevention and control of geological disasters and regard the prevention and control of geological disasters as a "life project". In order to implement this requirement, the municipal party committee and the municipal government have carried out centralized and special rectification of disaster prevention and control throughout the city, and carried out large-scale publicity, drills, investigation and rectification. The disaster prevention and control will be included in the target assessment of governments at all levels, and the responsibility system for prevention and control will be established and implemented point by point for the hidden dangers of disasters that have been identified. A county-level leader will be implemented at the monitoring points above the municipal level, and a department-level leader will be implemented at the county-level monitoring points. The responsibility for disaster prevention was implemented step by step, and the member units of emergency headquarters actively participated in the disposal of geological disasters, which laid a solid foundation for the successful risk avoidance.

(2) Adhere to the monitoring and early warning mechanism. In the process of weather turning cloudy, timely consult with meteorological departments, pay close attention to the changing trend of rain conditions, and dynamically release monitoring and early warning information, forming a top-down geological disaster early warning and forecasting release mechanism. August 18 Before the Yinjiangwan landslide occurred in Shunhe Village, Longshan Town, Gulin County, the land and resources departments of provinces, cities and counties issued early warning information of geological disasters intensively and dynamically according to the rain information notified by the meteorological department. The early warning information was quickly transmitted to the full-time monitor of the hidden danger point of geological disasters in Yinjiang Bay, Shunhe Village, Longshan Town, Gulin County. Full-time monitoring and timely detection of dangerous situations and early warning are important prerequisites for this successful hedging.

(3) Establish a team of full-time supervisors at the grass-roots level. According to the requirements of ministries and agencies, city and county governments have established and improved a team of full-time monitors, requiring each monitoring point to be equipped with more than two full-time monitors, and training full-time monitors every year to comprehensively improve the monitoring level and emergency response capability. In this rainfall, the full-time monitoring personnel of Jiushe, Shunhe Village, Longshan Town, Gulin County worked solidly. Adhere to the dynamic investigation and inspection of hidden dangers of geological disasters in flood season, carry out 24-hour uninterrupted monitoring and inspection as required, issue early warning in time after discovering dangerous situations, and immediately report to the disaster site through semiconductor speakers and propaganda. And ask the personnel at the disaster site to evacuate to a safe area immediately according to the exercise route. People often refer to monitors as propagandists, commanders and security guards on the front line of geological disasters. It is the life guardian of people in hidden dangers.

(4) Strictly implement the "three avoidance" measures. Once the meteorological warning information of geological disasters is released, resolutely organize the masses to prevent evacuation in advance according to the plan. During the period of heavy rainfall from August 16 to August 18, the city took the initiative to avoid danger 3 1 hidden danger points in advance, with 809 people, including 608 people in 24 places in Gulin County. On August 17, the rainfall in Longshan Town reached 147.7mm, and at dusk on August 17, the Jiushe landslide monitoring point in Shunhe Village made preparations for villagers to visit relatives and friends, resettle nearby, evacuate people and give early warning signals. Only when the danger is discovered at night can we decisively organize the orderly evacuation of the masses.

(5) Enhance people's awareness of disaster prevention and avoidance through training and drills. In recent years, through government-led, departmental organizations and mass participation, the city has organized various forms and rich contents of publicity and training on disaster prevention and avoidance and emergency drills, which greatly improved the people's ability and autonomy in disaster prevention and self-defense. Every year, the town government will organize an emergency escape drill for geological disasters at the hidden danger point of Yinjiang Bay in Shunhe Village, Longshan Town. When disaster comes, people can evacuate quickly according to the established route.