"5 9" Guangkengcao landslide disaster in quanzhou county, Guilin, Guangxi.

Guangkenggao landslide of Luojiang Village Committee in quanzhou county, Guilin is located at the back of Guangkenggao quarry in Luojiang Village, quanzhou county. The length of the landslide along the slope is 100m, the width is 76m, the thickness of the landslide is 3 ~ 35 m, the average thickness is about 25m, and the total scale of the landslide is about 200,000m3. The landslide body is mainly composed of Quaternary residual, Cambrian sandstone, mudstone, siltstone and some moderately weathered Jiangjiashan Formation granite (Caledonian). On May 9, 20 1 1, the landslide slipped from 13: 30 to 13: 30, and the coordinate of the center point of the landslide was 1 10 40' 59 "in east longitude and 25 49" in north latitude.

The landslide killed 22 people, injured 1 person, destroyed many sets of production equipment such as large excavators, transport vehicles and domestic vehicles, and buried 6 mobile homes (construction area is about 1000m2). The direct economic loss is estimated to be more than 3.5 million yuan. After the disaster occurred, all personnel and equipment in the landslide danger zone were evacuated quickly, without causing further casualties and property losses.

Figure 1 Landslide Panorama (photo direction 220)

2 regional geological environment conditions and genetic trend analysis

2. 1 Regional geological environment conditions

The landslide area belongs to subtropical humid monsoon climate, with Yuechengling mountain system in the northwest, Dupangling mountain system in the east, Haiyang mountain in the south and low terrain in the middle. The annual average temperature 16 ~ 18.5℃ and the annual average rainfall1156 ~ 2601mm. Rainfall is mainly concentrated from April to July, accounting for 57% ~ 75% of the annual rainfall. According to the data of the weather station in Xianshui Town (4km from Xianshui Town Reservoir), the rainfall in the landslide area was 12: 00 from May 8 to noon on May 9, which was a rainstorm (Figure 2).

Fig. 2 Landslide plan

The mountain where the landslide is located is of medium-low mountain landform, with an elevation of 400 ~ 700 m, a relative height difference of 100 ~350m, and an elevation of 70 1 at the top of the landslide. The valley under the slope is 370m above sea level, with a relative height difference of 33 1. 9m, the slope is 60 ~ 75, and the mountain is steep.

The landslide area is located at the edge of Yuechengling granite body in northern Guangxi, which is porphyritic biotite adamellite in Jiangjiashan unit. There is a small area of Cambrian mudstone stratum in the landslide area, which belongs to the capture body of igneous intrusion. Granite rock mass and CAMBRIAN strata as "capture bodies" in landslide area have strong weathering, developed fractures and deep fractures. The thickness of the slope eluvial layer on the mountain surface is 5 ~ 10m. Below the slope eluvial layer are granite and Cambrian mudstone, with strong weathering cracks and structural cracks.

2.2 Landslide characteristics

The main sliding direction of the landslide is 80. The length of the landslide along the slope is 100m, the width is 76m, the thickness of the landslide is 3 ~ 35 m, the average thickness is about 26 m, and the total scale of the landslide is about 200,000m3. Landslide is mainly composed of Quaternary residual, Cambrian sandstone, mudstone, siltstone and some moderately weathered Jiangjiashan granite (Caledonian). The sliding layer is mainly composed of moderately weathered Jiangjiashan granite (Caledonian), and a few upper sections are moderately weathered Cambrian sandstone, mudstone and siltstone. A steep wall with a width of 76m and a height of 73m is formed at the trailing edge of the landslide, which can be seen on the steep wall.

After the landslide, the sliding body first slides down to 80 from the height with a relative height difference of 1.75m, and then jumps, rolls and slides along the slope for 200m before being blocked by the mountain in front. Part of the sliding body (volume about 1 0,000m3) smashed the barrier and washed down the back of the barrier. The rest of the sliding body turned to 350 and pushed forward 1m, and was blocked by the mountain again 100m and pushed to 58, then pushed to 328 by 150m, and finally piled up.

In the process of landslide sliding to the front valley at high speed, the rock and soil at the bottom of the valley and on the hillside are scraped, and the landslide volume is greatly increased. At present, the valley * * accumulation layer 150000 m3, and the proportion of soil and rock in landslide accumulation layer is about 1: 1. The largest stone is 6 ~ 7 meters in diameter and its volume ranges from 0. 5 ~ 100 m3。 There is still1500,000m3 loose rock and soil on the hillside in front of the landslide.

There are quarry sheds and stockyards in the lower reaches of the valley section, and the slipper quickly buried the sheds and stockyards, causing the sheds to be completely destroyed and buried, causing 22 deaths, 1 person being injured, and many sets of production equipment such as large excavators, transport vehicles and domestic vehicles being destroyed. Bury 6 mobile homes (construction area is about1000m2); The direct economic loss is estimated to be more than 3.5 million yuan.

2.3 Cause analysis and trend judgment

According to field investigation and comprehensive analysis, the causes of landslide disasters are closely related to factors such as stratum lithology, topography, local rainfall, quarry mining and so on.

The landslide is located in the middle and low mountain landform area with a peak elevation of 70 1. The elevation of the toe valley is 370m, the relative height difference is 33 1.9m, the mountain is steep, and the slope is 60 ~ 75, which provides a favorable free surface for landslide.

The strongly weathered layer in granite mountain area is prone to landslide, and the Quaternary eluvial layer is thick. The maximum thickness of strongly weathered granite layer in the original area of landslide is 30m, generally 10m. Quaternary eluvial layer is 1 ~5m thick, with loose soil structure and good water permeability. Landslide is located at the interface between clastic rock and granite. There is a NE-trending fault passing through about 1 ~ 2 km northwest of the landslide, and rock mass, rock mass joints and structural cracks are developed in the landslide area.

According to the data of the nearest rainfall station in Shandong province (7. From the landslide point 1km), from May 7 to 9, the maximum 0-hour rainfall is 1.0 mm, which is 120. 5mm hour 165. Five millimeters and six hours. In the landslide area, from continuous rainstorm to heavy rainstorm, a large amount of rainwater falls to the ground, which leads to the infiltration of surface runoff into the residual pores of loose slopes and the joints and cracks of strongly weathered clastic rocks and granite rocks, which makes the loose and broken rock and soil in a wet saturated state, and its self-weight increases, and the friction force decreases after the rock and soil are soaked in water.

According to the field investigation in the landslide area, four seasonal springs flowed out with the rainfall (moderate rain, rainfall greater than 30mm, measured during the landslide) at the elevation of 520 ~550m m. According to the interview, no spring flowed out before the landslide. Accordingly, before the landslide occurred, a large amount of rain fell to the ground, which led to the infiltration of surface runoff into the loose pores of the slope eluvial layer and the joints and cracks of the strongly weathered clastic rock and granite rock mass (rock), which made the pores and joints and cracks of the loose and broken rock mass saturated with water and the hydrostatic pressure in the rock mass increased.

On both sides of the landslide area are quanzhou county Guangkengcao Quarry (a quarry suffering from landslide) and quanzhou county Mingtai Quarry, which have been mined for many years. The mining edges of the two quarries are 70m and 200m away from the landslide edge (sliding boundary) respectively. It is understood that the blasting in quarry mining is a small explosive blasting, and its blasting vibration is small, but its blasting may have a slight impact on the development of rock cracks in landslide areas.

According to the field investigation, the landslide has slipped away from the sliding surface, moved nearly 500m along the slope surface and accumulated in the groove, with a volume of about 6,543.8+500,000 m3, but there is still 6,543.8+500,000 m3 of loose rock and soil on the sliding bed surface. In addition, there are tensile cracks about 20m long and 5 ~ 8cm wide on the wall at the rear edge of the landslide, and the soil layer of the slope is thick, and the lower part is open, so the stability of the landslide slope is poor. Once it encounters continuous heavy rainfall, the slope may collapse again.

3 emergency response and disposal measures

3. 1 emergency response

After the landslide, quanzhou county immediately launched a Class I emergency response to sudden geological disasters, and all emergency teams rushed to the scene at the first time. Technicians from the Department of Land and Resources of Guangxi Zhuang Autonomous Region and Guangxi Geological Environment Monitoring Station immediately rushed to the site for investigation, carried out emergency monitoring of landslide disaster points and other disposal technologies, and carried out emergency investigation of geological disasters, which provided strong technical support and support for emergency rescue and disaster relief and prevention of secondary geological disasters.

On 2011May 10, the Ministry of Land and Resources sent an expert group to the site for emergency treatment and technical guidance on disaster consultation, and submitted the Brief Report on Preliminary Investigation of the Landslide in Guangkengcao Quarry, Xianshui Town, quanzhou county at 23: 00 that night. On May 14, a team of 23 people from Xianshui Town, quanzhou county City, Guilin City, investigated the landslide again.

3.2 Emergency treatment

(1) During the emergency construction, strengthen the monitoring of the residual sliding body and the cracked soil and cracks above the trailing edge wall to prevent the secondary disasters from harming the emergency personnel.

(2) Drain and dredge both sides of the accumulated sliding body in the ditch to prevent the possibility of debris flow caused by accumulated water.

(3) Strengthen the investigation of areas with similar geological environment conditions around the landslide to prevent such disasters from happening again.

(4) After the rescue work, the accumulated deposits in the valley area shall be leveled with the slope of 1: 1.25.

(5) Build drainage ditches on both sides of gully landslide deposits, and use open ditches to divert rainfall and flood, so as to prevent the formation of weirs from causing geological disasters of debris flow and protect the safety of downstream villages.

(6) Loose deposits and landslide deposits in the spoil ground of Mingtai quarry on the hillside are covered with ponchos to prevent rainwater infiltration and erosion, and do a good job of drainage and guidance.

(7) Monitoring piles should be set up for the unstable slope formed in the spoil ground of Mingtai quarry to monitor the deformation and change of the unstable slope, and corresponding measures should be taken in time if any abnormality is found.

(8) Delineate the scope and boundary of this major hidden danger area, set up wire fences on the boundary for isolation, and set up warning signs to prohibit personnel from entering, so as to avoid causing heavy casualties and ensure the safety of people's lives and property (Figure 3).

Figure 3 Rescue site

4 Experience and Enlightenment

The occurrence of this landslide geological disaster and its heavy casualties and economic losses (the disaster level is relatively high) show that the knowledge of geological disaster prevention should be popularized not only by the original residents, but also by the employees of various industrial and mining enterprises with high mobility. The construction, production and part of life activities of various industrial and mining enterprises must be arranged in accordance with the requirements of risk assessment of geological disasters, and the monitoring and prevention of geological disasters should be done well.

(This part of the basic information is provided by the Department of Land and Resources of Guangxi Zhuang Autonomous Region, edited by Wei)