1 Preface
On February 18, 2013, at about 11:37 pm, a landslide occurred in Laoshan Xincun, Fork River Group, Fishing Cave Village, Longchang Town, Kaili City, Qiandongnan Prefecture, Guizhou Province, at the geographic coordinates of 107°54′31.3″E, 26°42′33.5″N. A sporadic falling, rockfalls, and sliding of cave fill occurred on the slope surface and in the cave at the upper part of the collapsed mountain body. The slope surface and the upper cave of the collapsed body continued to have sporadic falling blocks and rocks, as well as sliding and collapsing of cave fillings, and at 8:30 p.m. on February 19th, a small-scale collapse occurred once again. The collapse body was 186m high, 127m wide, 10-24m thick, and the size of the collapse pile was about 300,000m3 (Figure 1). The collapse pile is distributed in the valley of Yuandong River, blocking the river channel, the river gradually congested, flooding the coal mining sheds near the river bank, forming a small weir. After investigation and verification: this disaster **** caused 5 people dead and missing. The scale of this landslide rating for large, disaster rating for medium.
Figure 1 Kaili Landslide in Guizhou
2 Geological Hazard Characteristics
2.1 Regional Geological Conditions
2.1.1 Topography and Geomorphology
The area of the landslide is a dissolution and erosion landform. The left bank of Yuodong River has high and steep slopes with slope inclination of 100°~130°, gently inclined reverse slope, and asymmetric U-shaped river valley geomorphology. The terrain is strongly cut, the terrain is complex, with large undulations, and there are a large number of collapse deposits along the riverbed. The right bank of the river valley is a steep-slow (approximate platform)-steep zigzag terrain, and the natural slope on the left bank is 75°～85°, with local concave rock cavities, and the relative elevation difference reaches 217m, and the original terrain is distributed with a narrow-type small platform in its center, and the local terrain has been changed by the collapse of the mountain body, and the slope body is now in the form of near-erect, with the upper part of the slope body protruding outward to form a nearly upright shape. The upper part of the slope body protrudes outward to form an inverted rock cavity.
2.1.2 Stratigraphic lithology and geological structure
The landslide is located in the north-west flank of the LuiGongShan complex fold tectonics, the east flank of the NNE-oriented Fishing Hole Directional Diagonal, and the upper plate of the NNE-oriented Datang Fault, with the fault plane yielding 45°～50°∠70°, the slope spreads out the Permian Lower Qixia Formation (P1q) medium-thick layered tuffs, and the foot of the slope is composed of the coal-bearing mudstone and shale of the Lower Liangshan Formation, with monoclinic output of rock layers. The shale at the foot of the slope is coal mud-bearing shale of the Liangshan Formation of the Lower Permian, and the rock stratum is monoclinic, with the shape of 325°∠9°. Under the influence of regional tectonic structure, the NNE and NW directions of the area have developed the large-scale fissures, and there are three groups of large-scale joints and fissures along the river slope, one group of joints is 125°～135°∠65°～80°, which is in the shape of closure, and is a hard structural surface; the other group of joints is 75°～85°∠70°～80°, which is a hard structural surface in the form of closure; and the third group is 270°∠80°～87°, which is half-open, without filling, and has no filling. The third group of nodules, 270°∠80°～87°, is half-open and not filled.
The carbonate rocks and clastic rocks are mainly distributed in the area, and the exposed strata include the Quaternary System (which is thinly distributed in the area), Permian Qixia Formation, Maokou Formation, and Liangshan Formation. The stratigraphy is divided from top to bottom as follows:
Quaternary loose layer (Q): yellow and yellow-brown residual slope deposit clay, hard - plastic state, containing chert breccia, particle size of about 0.02 ~ 2cm, content of 10% ~ 30%, soil layer is about 3 ~ 7m thick.
Permian Qixia, Maokou Formation (P2q + m): the bottom lithology for the dark gray, medium-thick to thick layers of bioclastic chert, with siliceous clumps; top of the Qixia Group, Maokou Group, Liangshan Formation, and the Liangshan Group. with siliceous clasts; the top is light gray thick-bedded massive chert. Stratigraphy is weakly developed, while joints and dissolution fissures are more developed. The maximum diameter of the cavern is about 2.5m, which is filled with yellow clay, and the direction of the cavern extends to the surface, and the collapse of the cavern leads to the formation of a funnel-shaped pit on the surface.
The Permian Liangshan Formation (P2l): the lithology is black and gray-black charcoal shale, clayey shale, and mineable coal beds, with a thickness of about 20 m.
According to the survey, under the influence of the geological structure, the rock body is developed by joints and fissures and has a certain scale; especially in the riparian zone, the river undercutting leads to the increase of the air space surface, and the fissures are well penetrated, and the joints cut the rock body into diamond-shaped blocks of different sizes, so that the rock body has been cut into diamond-shaped blocks with different sizes. diamond-shaped blocks, so that the integrity of the rock body suffered damage.
According to the 1:4 million "China Earthquake Intensity and Dynamic Parameters Zoning Map" (GB18306-2001) and 1:4 million "China Earthquake Response Spectrum Characteristic Cycle Zoning Map", the peak acceleration of the earth tremor is 0.05g, the characteristic cycle of the dynamic response spectra is 0.35 s, and the basic intensity of the earthquake is VI degree. Late and recent tectonic activity is not obvious, and it is a tectonically stable area.
2.1.3 Hydrogeological Characteristics
Based on the lithology of the exposed strata in the area, the characteristics of the water-bearing medium, and the dynamic conditions of the groundwater, the groundwater can be divided into three types: carbonate karst water, bedrock (clastic rock) fissure water, and the pore water of the Quaternary Loose Layer. The pore water of the loose layer of the fourth system is mainly distributed in the alluvial and residual slope accumulation layer on both sides of the river valley, and the water content is relatively small; the main water-bearing rock groups of carbonate karst water are the Qixia Formation of the Permian System and the Maokou Formation, with the lithology of medium-thick layered tuffs, muddy tuff and dolomitic tuff, and the groundwater is mainly piped flow, and the water-rich nature is relatively good; the water-bearing rock groups of the bedrock (crushed rock) fissure water are the Liangshan Formation of the Permian System, and the lithology of these rock groups is coal-bearing mudstone shale, and the water-rich nature is weak. The water-rich nature is weak.
Groundwater is mainly recharged by atmospheric precipitation, and most of the atmospheric precipitation in the carbonate distribution area falls into the ground through waterfall holes and karst funnels, or infiltrates through the surface, forming karst water, which is transported through karst pipes and fissures, and is exposed as springs in low-lying areas of the terrain or at the contact surfaces of clastic rocks, and most of the water is discharged into the Yudong River through surface runoff.
2.1.4 Human engineering activities
The landslide is distributed within the Pingdi coal mine in Longchang Township, and about 100m upstream of the landslide is the main shaft entrance of the mine, which is a roadway excavated from the hard gray rock at the top of the coal seam. The coal mining sheds are built along the river, with the river flat as the building point, and human engineering activities are relatively strong.
2.2 Geological Hazard Characteristics
The mountain collapse body is about 186m high, 127m wide, 10-24m thick, and the size of the collapse pile is about 300,000m3, which consists of middle-thick layer to thick layer of chert in the Qixia-Maokou Formation of the Permian System, and the right edge of the collapse is bounded by a large-scale, steeply-standing jointed fissure with the direction of NWW, and a clear, nearly horizontal tectonic scuffing can be seen in the jointing surface with serious erosion phenomenon. The right edge of the collapse is bounded by a large NWW-oriented near-steep fissure, with clear near-horizontal tectonic scuffs visible on the face of the fissure, and the phenomenon of dissolution is serious and filled with yellow clay; the left edge is bounded by a cave formed by a near-dissolution fissure; and a dissolution joint fissure is also distributed parallel to the slope. Above the slope, there is still about 2000m3 of dangerous rock body remaining, the upper and middle part of the distribution of full-filled caverns, from the top of the slope 16-18m distribution of a karst collapse of about 20m in diameter, the karst collapse pit filled with gravel yellow powdery clay. The karst collapse did not appear in the surface survey before the collapse occurred, but was formed after the exposure of the cave after the collapse so that the material filling it was lost.
The collapse pile is distributed in the upstream of the intersection of Yudong River and the Two Forks of the River at about 150m, the pile is "oval" in size, distributed along the river, about 175m in length, about 128m in width, and the pile is about 27m in thickness at the thickest place. 5m, more than 2m of the total volume of the blocks accounted for about 35% of the total volume of the pile, more along the foot of the steep slope line distribution; length of 0.5 ~ 2m of the total volume of the blocks accounted for about 45% of the total volume of the pile, more distributed in the river, the other block size of about 20%. The formation of a small weir.
3 Analysis of the causes of geological hazards and trend judgment
Based on the characteristics of the collapse body, combined with topography and other geological conditions, the development of the river characteristics of the comprehensive analysis that: the collapse of the mountain is mainly controlled by the downslope NNS to the NWW direction of the two groups of large-scale joints cleavage to the formation of wedge-shaped block, the rock body is layered - fracture structure, the slope topography is steep, the formation of the unloading of the fissure of the flat shape on the slope surface The topography of the slope is steep, forming unloading fissures that are flat on the slope surface, and the degree of opening of the joints and fissures increases under long-term weathering and dissolution.
Due to the unfavorable slope structure of upper hard and lower soft with the strong influence of groundwater dissolution and weathering, the rock body is extremely unstable, as well as the long-term weakening of the bottom of the mining, which ultimately led to the generation of the collapse of the mountain, which is highly insidious and sudden. At present, the possibility of an overall large-scale collapse of the mountain is relatively small.
4 Geological disaster emergency prevention and control
Kaili municipal government immediately started the municipal disaster prevention plan to carry out emergency rescue, set up a cordon area and cordon line, Kaili (Kaili) Shi (Bing) secondary highway to carry out temporary traffic control, and the formation of a weir to take diversionary measures. After receiving the report of the disaster, the Department of Land and Resources of Guizhou Province organized a 40-member emergency expert group from the Guizhou Geological and Environmental Monitoring Institute to rush to the site to carry out field investigations and actively assist the local government in rescue and relief work. The Ministry of Land and Resources paid close attention to the situation and sent a geological disaster emergency expert group to the site to understand the danger of the disaster and the progress of rescue and relief work, to consult and guide the on-site rescue and relief work and emergency disposal, and to use three-dimensional laser scanning technology to quantitatively evaluate the basic features of the collapse body (Figure 2). In order to prevent similar disasters from occurring in neighboring areas, the local government organized and carried out an emergency geologic disaster investigation in the vicinity of the mountain for nearly 27km2, and used drones to take remote sensing aerial photographs of 7km2 in the vicinity of the disaster.
Figure 2: Measuring geometric parameters of the collapse body from point cloud data
5 Experience and inspiration
(1) This disaster reflects that in the fragile geologic environment, attention should be paid to the temporary shelter site, and the site of the temporary shelter should be protected from the disaster. The assessment of the risk of geologic hazards should be emphasized in the selection of the site for the temporary shed.
(2) In the emergency investigation of this disaster, high-tech means such as drone aerial photography and three-dimensional laser scanning were adopted, and the practice shows that the non-contact measurement technology plays an important role in the emergency working condition.