On July 7, Gedi landslide occurred in Yinjiang Tujia and Miao Autonomous County, Guizhou Province.

2014 At 3: 5438+07 on July 6th, a landslide occurred in Gedi Village, Huang Mu Town, Yinjiang Tujia and Miao Autonomous County, tongren city, Guizhou Province. Three people were injured in the landslide disaster, and 260 buildings 1 180 houses and a school collapsed in Gedi village, involving 334 households 1024 people. The direct economic loss was nearly 50 million yuan, but fortunately no one died. Landslides may cause secondary disasters, threatening the safety of 85 households and 325 people in Siguliang, Xiagedi and Podixia villages downstream of landslides, and the provincial roads from Yinjiang to Huang Mu and Huangmu to Heaven, with potential economic losses of nearly 1 100 million yuan.

2 General situation of geological disasters

2. 1 Geological environment conditions

(1) Terrain

The bottom landslide area is a deep valley slope landform with dissolution-invasion and erosion, and the micro-landforms such as terraces and ridges on the slope are staggered and developed. The overall terrain is high in the east and low in the west. The highest point in the area is located at the back peak of Gedi Village in the east of the investigation area 1033.45 meters, and the lowest point is located at the two forks river in the southwest of the investigation area, about 768.5 meters, with the maximum relative height difference of 264.95 meters. The original landform has been strongly transformed by human engineering and economic activities, and the overall landform is characterized by alternating distribution of platforms and slopes with a slope of 5 ~ 40.

② Formation lithology

The rock and soil layer distributed and exposed in the area is Quaternary cultivated soil layer (Qd) from top to bottom, with a thickness of 0.2 ~ 0.5m；; The eluvial silty clay is mixed with gravel layer and gravel soil layer (Qdl+el) with a thickness of 3.1~ 7.1m; The underlying bedrock is the middle-thick bedded marl of the Lower Ordovician Dawan Formation (O 1d), which is divided into strongly weathered layer and moderately weathered layer. Strongly weathered marl is broken, with a thickness of 2.5 ~ 8.6m ..

(3) Hydrogeological conditions

According to the strata lithology, water-bearing medium and groundwater dynamic conditions exposed near the landslide area, the groundwater types in the area are mainly Quaternary loose layer pore water and bedrock fissure water. Pore water in the Quaternary loose layer exists in the Quaternary loose layer in the form of stagnant water in the upper layer, which is mainly replenished by atmospheric precipitation and gentle catchment at the top of the slope. Part of it supplies the underlying bedrock cracks through vertical infiltration, and the other part is discharged from the free surface and low-lying areas in a dispersed form, with weak water abundance and water quantity mainly controlled by rainfall. Bedrock fissure water is mainly concentrated in bedrock joint fissure in the form of diving, and the main recharge sources are the lateral recharge of the plane catchment area at the top of the mountain, the vertical recharge of the pore water in the Quaternary unconsolidated layer and the atmospheric precipitation recharge, which has a good hydraulic connection with the pore water in the overlying unconsolidated layer. Most of the water is discharged along the 270 slope, exposed in the form of spring water on the east bank of the gully on the west side of Gedi Village, converted into surface water, and finally discharged into Huangmu River along the gully; Disperse and discharge a small amount of water in the exposed bedrock or low-lying areas of Gedi and Toli villagers' building areas.

2.2 Disaster scale and scope of influence

The landslide is located in Gedi Village, Huang Mu Town, Yinjiang County, with a trumpet-shaped overall plane and an overall sliding direction of 283. See photo 1. From the trailing edge of the landslide to the top of Gedi village, it basically reaches the second watershed position; The front of landslide is located at the bottom of Duimengou at the foot of slope. In the process of landslide, the sliding body was cut from the bottom of Duimengou, which caused the surface to uplift and pushed a long distance along the sliding direction. The front edge of the sliding body crosses the gully and reaches about 85 m on the right bank of Duimengou. The left and right sides of the landslide are bounded by the slope break and the gully edge line.

Figure 1 Panorama of Gedi Landslide

The width of the trailing edge of the landslide is175m, the width of the leading edge is 530m, the inclined length of the landslide is 615m (excluding 85m pushed to the right bank of Duimengou), the average thickness of the landslide is 1 1 m, and the volume of the landslide is about 238.47×104m3.

Fig. 2 Landslide characteristics

According to the terrain restoration, local villagers' reflection and site investigation, the houses in Gedi Village slipped about150m along the 250 direction during the landslide deformation and sliding. Tuoli Village slides along the direction of 245 100 meters, and some houses rush up the slope about 50 meters on the right bank of Duimengou with the landslide.

2.3 Causes of occurrence

The formation of landslide geological disasters has the following four factors.

(1) Topographic and geomorphological conditions

The narrow platform and short slope of the landslide are distributed alternately, and the top of the slope is a gentle platform, with a large number of paddy fields, good water collection conditions and abundant external water sources. The middle and front of the landslide are stepped slopes formed by human engineering activities, which change the original topographic conditions and aggravate the deformation of the slope rock and soil.

② Geotechnical structure

The slope direction of the landslide is 307, the slope10 ~ 35, the occurrence of underlying bedrock is 285 ∠ 23, and the slope structure is along the slope, which is an unfavorable factor affecting the slope stability. The upper landslide is Quaternary (Q) overburden and strongly weathered marl. Joints and cracks in strongly weathered bedrock are developed, and there are weak interlayers with poor mechanical properties. When the sliding force of the upper landslide exceeds the sliding resistance, the sliding surface of the landslide will shear along the weak interlayer.

(3) Atmospheric rainfall

Before the Gedi landslide, it rained continuously for half a month in Yinjiang County, especially on July 6 (14), the day before the landslide, Huangmu Town suffered a rainstorm lasting about 8 hours, with the rainfall exceeding 200 mm. Part of sudden precipitation flows to low-lying areas along the surface gullies, which accelerates the formation of landslide boundaries and reduces the lateral sliding resistance of landslides. The slope at the top of the landslide is gentle, and the slope soil that constitutes the landslide has loose structure and good water permeability, and the bedrock at the lower part is relatively waterproof. Under the action of atmospheric rainfall, some rainfall and domestic production water are discharged from surface runoff, and the other part is vertically infiltrated and discharged along the bedrock surface of the landslide front and low-lying areas on both sides. On the one hand, the self-weight of landslide increases, the mechanical properties of soil decrease, the water content of sliding zone soil increases and the shear strength of sliding zone soil decreases; On the other hand, the seepage pressure generated by rainfall in the sliding body changes the hydrodynamic conditions of the slope rock and soil. Increasing the sliding force of landslide and reducing the sliding resistance of landslide will aggravate the deformation of slope and lead to instability and failure.

④ Human engineering economic activities

Gedi village, as a village around Huangmu town government, has good economic conditions and is one of the richest villages in Huangmu town. With the continuous improvement of economic conditions in recent years, a large number of small houses with three or four floors have emerged on the slope, which greatly increases the load of the slope (geological environment), reduces the critical state of slope stability, and accelerates the deformation and sliding of the slope.

3. Geological hazard inspection and monitoring

3. 1 Daily inspection and monitoring

In previous detailed investigations, investigations and daily inspections, no abnormality was found in the disaster area, which does not belong to the hidden danger point of geological disaster monitoring.

3.2 Identification and early warning of dangerous situations

(1) Identification and judgment: In the construction of "Ten Counties" and "Five Places" for the prevention and control of geological disasters in our county, villagers in disaster areas can be vigilant according to the common sense of geological disasters and identify the signs of impending landslides.

(2) Start the early warning mechanism: the villagers who find the danger report to the village cadres in time, and the village cadres immediately report to the town government and actively organize self-help. The town government immediately launched an emergency plan after receiving the report, and organized villagers to evacuate the dangerous area in a timely and orderly manner, without causing casualties.

4. Safe haven resettlement for geological disasters

4. 1 emergency treatment

After the occurrence of geological disasters, the municipal party committee and municipal government immediately launched the municipal disaster prevention plan, provided emergency assistance to the affected people and construction workers, and reported it to the superior land and resources department.

4.2 Temporary Resettlement and Restoration and Reconstruction

(1) The local people's government properly arranged the production and life of the affected people, actively carried out ideological work for the affected people, and maintained social stability.

(2) Strengthen the vigilance and monitoring of landslide danger areas and implement traffic control. Before the landslide treatment, people and vehicles are strictly prohibited from passing through the dangerous area, and before the landslide disaster stabilizes, people are prohibited from entering the disaster group to rush to transport materials;

(3) Because there are still some free surfaces on both sides of the front edge and the rear edge of the landslide, it is very likely that the landslide will happen again, so the emergency rescue work must ensure the safety of personnel.

(4) Speed up landslide control, and carry out control design and construction as soon as possible.

(5) Strengthen the propaganda of geological disaster prevention knowledge, and improve people's awareness of geological disasters, prevention and avoidance.

5 Experience and Enlightenment

(1) The Party committee and government attach importance to the prevention and control of geological disasters.

② Pay attention to the propaganda of geological disaster prevention knowledge.

(3) Firmly build a group prevention and treatment system.