The Baishilazi section of Changbai County, Jilin Province collapsed.

20 1 165438 2003+10/at 3: 00 am on October 23rd, the Baishilazi section of Shenchang Line (381k+200m-) located between Jiguanlazi Village and Lenggouzi Village in Shisidaogou Town, Changbai Korean Autonomous County, Jilin Province. When the disaster occurred, no vehicles passed through the affected sections, causing no casualties. The collapse caused damage to the 200-meter-long highway, which blocked the Linjiang-Changbai section of the Shenchang line and blocked the traffic. After the disaster, the competent departments of land and resources of provinces, cities and counties immediately launched the emergency plan for sudden geological disasters and organized experts to rush to the disaster site to carry out emergency investigation and disposal.

2 Geological hazard characteristics

2. 1 regional geological environment

(1) Terrain

The disaster occurred in the lava plateau area, and the landform type was lava plateau landform. The plateau has flat surface, high river density, deep cutting depth and V-shaped valley.

(2) Formation lithology

The exposed strata in Shidaogou Town, where the disaster occurred, include diorite formed in the early Yanshan period and granite intrusive rocks in the late Yanshanian period, most of which are exposed in the form of bedrock.

(3) Geological structure

The geological structure in this area is mainly Shibadaogou-Changbai syncline, which is located in the south of Changbai County. The syncline axis is NW-SE in the west of Shibadaogou, and gradually turns to NW-SE in the east. Both ends of the syncline extend into South Korea, with a length of about 100km from east to west and a width of 6- 12km on both wings, showing a strip shape.

(4) Hydrogeological conditions

Caves, primary joints and structural cracks develop in the subsidence area, which provides space for the occurrence and migration of groundwater. General spring flow is 1 ~ 10L/s, single well water inflow is 100 ~ 1000m3/d, the hydrochemical type is mainly magnesium bicarbonate, and the salinity is less than 0.3g/L. ..

(5) Meteorological conditions

Shidaogou Town belongs to the continental humid monsoon climate in the north temperate zone. The climate is characterized by long and cold winters, short and rainy summers and distinct seasons. The annual average temperature is 2. 13℃, the annual accumulated temperature is 2500℃, and the frost-free period is about 120 days. Over the years, the dominant wind direction in Shidaogou Town is southwest wind, with an average annual precipitation of 622.35 mm and a maximum precipitation of 82.4 mm. ..

2.2 Geological hazard characteristics

The collapsed mountain is a vertical steep cliff, and there are three groups of joints in the rock mass (dip angle 3 10, dip angle 90; Go down 280, go down 80; The dip angle is 95, and the dip angle is 7). The above joint combination reduces the integrity of rock mass, which is an unfavorable combination and provides a boundary foundation for the occurrence of collapse. The joint with nearly vertical dip angle is the key structural plane leading to collapse, as shown in Figure 1-3.

Figure 1 Panorama of folded body

2.3 Disasters and dangers

The collapse is located between Lenggouzi Village and Jiguanlazi Village in Shisidaogou Town of Changbai Korean Autonomous County, 38 1K+200 m to 38 1K+400 m away from Baishilazi section of Shenchang Line. The landslide blocked the 200-meter-long section of expressway, and the height of rockfill from the road surface to the highest point of accumulation slope reached 260 meters, which interrupted the Linjiang-Changbai section of Shenchang long line and damaged some subgrade. The collapse is near the Yalu River, and the width of the river that flows through it is about 100m. The collapsed sediments fill the Yalu River, and the width of the blocked river is about 2/3, and the downstream length is more than 200m, and the blocked river area reaches 70%.

Figure 2 Yalu River collapse

Fig. 3 shows that there is still a small collapse.

3 Geological hazards cause analysis and trend judgment

3. 1 disaster cause analysis

(1) internal structure

There are three groups of joints in the rock mass where the collapse occurred, namely, the dip angle is 3 10 and the dip angle is 90; Go down 280, go down 80; The inclination angle is 95 and the inclination angle is 7. It is easy to see that two groups of structural planes are relatively vertical, and the other group is close to horizontal. This joint combination reduces the integrity of rock mass and provides structural conditions for the occurrence of collapse, in which the joint with near vertical dip angle is the key structural plane leading to collapse.

(2) external dynamic conditions

Snowfall and frost heaving are two external dynamic conditions of this collapse. Before the collapse, there were large-scale snowfalls and even local blizzards in Jilin Province. With the increase of snow, the load of dangerous rock mass also increases. 1 1 year1in late October, with the gradual entry of winter in the north, the temperature dropped continuously, and the cracks in the rock mass gradually penetrated under the action of frost heaving, which also provided favorable conditions for the occurrence of collapse.

3.2 Disaster trend judgment

After the collapse is basically stable, with the gradual stabilization of the temperature and the end of the heavy snowfall in Changbai County, the factors that are conducive to the collapse are reduced, and it is unlikely that the collapse will occur again. However, after the disaster, the collapse body and its forming environment have not been fully and carefully investigated, so it should be carried out as soon as possible. If there is heavy snowfall again, we should strengthen the monitoring of the collapsed body and its nearby dangerous rock mass.

4. Emergency prevention and control of geological disasters

According to the relevant contents of the Emergency Plan for Sudden Geological Disasters in Jilin Province, the emergency response of large-scale geological disasters (level II) is started. After the collapse, the local competent department of land and resources immediately reported it to the Jilin Provincial Department of Land and Resources, which immediately appointed the Jilin Provincial Geological Disaster Emergency Technical Guidance Center to form an expert group, and conducted a detailed survey of the collapse site together with relevant leaders of the local government and relevant personnel of the Department of Land and Resources. And discussed and formed a preliminary disaster cause, mechanism judgment, and post-disaster emergency treatment advice. On the basis of field investigation, the expert group of Jilin Geological Disaster Emergency Technical Guidance Center put forward emergency treatment opinions: the collapse has been basically stable and can be cleaned up; Cleaning work must be carried out from top to bottom. Clean up the dangerous stones on the steep cliffs first, and then clean up the gravel piles and roads from top to bottom. In order to ensure construction safety, observation work must be strengthened during construction; In order to pass through Shenchang expressway safely and quickly, it is suggested that blasting be used to remove the gravel accumulated above the road surface.

5 Experience and Enlightenment

In recent years, extreme abnormal weather occurs frequently in Jilin Province, and the hidden danger points of geological disasters are in the process of dynamic change, which puts forward higher requirements for early warning and emergency prevention of geological disasters. Through the emergency treatment of Baishilazi collapse in Changbai County, the following experiences are obtained:

(1) In case of extreme or abnormal weather conditions within the jurisdiction, it is necessary to strengthen the inspection and monitoring of the identified hidden points of geological disasters. For traffic facilities seriously threatened by geological disasters, measures such as rerouting and bypassing should be taken. If it is impossible to reroute, obvious warning signs and warning lines should be set up.

(2) When the highway and railway lines are damaged or interrupted due to geological disasters, the emergency plan should be started immediately, and the relevant departments should take effective measures to clean up and open the lines as soon as possible to ensure the normal life and social and economic activities of the local people.

(3) It is urgent to study the formation mechanism of landslides in cold regions.