(The First Hydrogeological Engineering Geological Team of Henan Bureau of Geology and Mineral Exploration and Development, Xinxiang, 453002)
Henan Baoquan Pumped Storage Power Station is a national key construction project, located in Zhongshan District, where geological disasters such as collapse, landslide and debris flow are relatively developed. This paper analyzes and discusses the distribution and characteristics of various geological disasters in the site, evaluates their risks, and puts forward corresponding geological disaster prevention measures.
Keywords: geological disaster investigation and risk prevention measures of Baoquan Pumped Storage Power Station
Baoquan Pumped Storage Power Station in Henan Province is located in Baoquan Reservoir on Yuhe River in huixian city, Henan Province. The installed capacity of the pumped storage power station is 1200MW, the annual power generation is 21100 million kw h, and the annual pumping power consumption is 2.642 billion kw h, which is a daily regulated pure pumped storage power station with a comprehensive efficiency of 0.76. After the power station is completed, it will be connected to Xinxiang 500kV substation with 500kV primary voltage double-loop outgoing line, and undertake the tasks of peak load shedding, emergency standby and frequency modulation in Henan power grid. This is an important national construction project. The power station consists of upper reservoir, lower reservoir, water diversion and power generation system and ancillary facilities.
The construction site of Baoquan Pumped Storage Power Station in Henan Province is located in Zhongshan District, with relatively developed geological disasters, large topographic relief, complex geological structure, unstable lithology and lithofacies, intense human engineering activities and complex geological environment conditions. This work adopts the methods of data collection, field geological disaster investigation and comprehensive analysis. This paper analyzes and discusses the distribution and characteristics of various geological disasters in the site, evaluates the risk of geological disasters, and puts forward the corresponding preventive measures of geological disasters.
1 Types and characteristics of geological disasters
According to the comprehensive investigation of geological disasters in the field, there are geological disasters such as collapse, landslide and debris flow in the construction site of Baoquan Pumped Storage Power Station in Henan Province, and their distribution and characteristics are as follows:
1. 1 crash
The collapse bodies in the evaluation area are densely distributed, mainly on the bank of the reservoir and the steep wall in front of the mountain. Their genesis and distribution are obviously controlled by topography, lithology and structural conditions. The main types of collapse are limestone collapse and timely sandstone collapse.
(1) limestone collapse:
It is mainly distributed on limestone cliffs of Maozhuang Formation (Lower Cambrian) and Zhangxia Formation (Middle Cambrian).
Maozhuang Formation limestone () distributed between 770-820m above sea level and Zhangxia Formation limestone () above 900m above sea level have medium-thick layered structure, hard lithology and great brittleness, and weathering and unloading cracks are developed in the rock mass, which makes some rock masses break away from the parent rock to form dangerous rocks. Dangerous rocks are widely distributed and have poor stability. Under the action of gravity, earthquake, precipitation and other factors, the dangerous rocks are unstable and collapse, and roll down the hillside. Most of the collapses are irregular in shape and different in size, with a volume of 3.0 ~ 135 m3.
(2) timely sandstone collapse:
It is mainly distributed in the cliffs formed by shallow metamorphic sandstone of Ruyang Group in Mesoproterozoic.
Topographically, the shallow metamorphic Mesoproterozoic Ruyang Group timely sandstone () formed a steep wall nearly 1.60m high, which made the rock mass open. Under the action of structural joints, weathered joints and unloading joints, dangerous rocks are formed in some areas and widely distributed. In addition, the existence of silty shale interlayer in rock mass leads to poor stability of dangerous rock mass, which is unstable under the action of gravity, earthquake and precipitation. This kind of collapse generally appears in the following two forms: one is that the crack at the rear edge runs through from top to bottom, and the weak interlayer at the bottom forms a rock cavity, which leads to collapse; The other is that the crack at the rear edge is wide, and the dangerous rock mass slides along the weak interlayer, forming a landslide. Collapse bodies are mostly rectangular, with different sizes, with a volume of 6 ~ 350m3 and a maximum of 22× 104m3.
1.2 landslide
Guishan landslide is the main landslide in this area, which is located on the steep cliff on the left bank of the lower reservoir of the power station 160m, facing the air. The sliding direction is down the reservoir, which directly threatens the safety of the power station. Its characteristics are described as follows:
1. range
The south and southwest boundary of the landslide is Yu He River, the east boundary is the bending zone developed by Shantou Formation, Maozhuang Formation and Xuzhuang Formation, and the west and northwest boundary is the river valley. Guishan landslide is 550-800 meters long from east to west and 260-350 meters wide from north to south. The maximum thickness of landslide is 2 10m, the average thickness is about 1 10m, and the volume is 21100,000 m3. This is a huge landslide.
2. Sliding body
Landslide strata are lower CAMBRIAN Mantou Formation (), Maozhuang Formation (), Middle CAMBRIAN Manxuzhuang Formation () and Zhangxia Formation () in turn from west to east, and the main strata are limestone and dolomite of Zhangxia Formation (). Most of the surface of the landslide has been cemented, and the interior is generally complete, basically maintaining the original rock structure. The bottom interface of landslide is flat and smooth, which is a friction mirror.
3. Sliding belt
The sliding zone is marl at the bottom of the first member () of the Lower Cambrian Shantou Formation, and the thickness of the sliding zone at the bottom is 0 ~ 15m. The lithology of the sliding zone is composed of breccia, silt and marl fragments. The breccia varies in size, showing subangular shape and argillaceous or calcareous cementation. In the area where the elevation of the sliding surface is 652 ~ 736 m, it is in the water level fluctuation zone.
4. Sliding bed
The main body of the sliding layer is the Mesoproterozoic Ruyang Group () shallow metamorphic sandstone.
5. Motion characteristics
Direction of movement: the sliding body generally slides west or southwest;
Sliding distance: the sliding distance of the leading edge sliding body can reach 5 10m, and the sliding distance of the trailing edge sliding body can reach 250m；;
Sliding time: According to the dating data of the materials in the sliding zone, the age of the sliding body ranges from 654.38+0.4 million to 265.438+0.0 million years, so it is judged that the sliding body was formed in the middle and late Pleistocene.
6. Formation and evolution of sliding body
The formation and evolution of Guishan landslide can be roughly divided into three stages.
The first stage: normal rock strata are eroded by faults, cracks and rivers, forming massive rock masses separated from surrounding rocks, with high and steep slopes and effective free surfaces at Yu He and Baoquangou;
The second stage: under the action of crustal movement and seismic force, the separated massive rock mass slides in the empty direction along the weak marl;
The third stage: after sliding, the sliding body is further influenced by geological tectonic movement, river erosion, weathering and human factors, forming the present landform.
1.3 Debris Flow
There are Donggou and Sigou in the debris flow gully in the evaluation area, and their characteristics are described as follows:
1. Donggou Debris Flow
Donggou is a tributary of the left bank of Yu He River, located in the east of Baoquan Village. The upstream is surrounded by mountains on three sides and has a water outlet on one side. The valley is V-shaped, and the downstream valley is U-shaped. The catchment area of the basin is 6km2, the length of the basin is about 4km, the slope of the basin is 30 ~ 40, and the longitudinal slope of the basin is 4% ~ 10%. The above landform conditions are favorable for the formation of debris flow.
The overburden of Donggou Valley is composed of slope proluvial, and its lithology is mainly gravel, block stone and loam, which is loose or semi-cemented. The thickness of valley bottom overburden is 0 ~ 15m, and the thickness of valley slope overburden is 0 ~ 6m. According to the investigation and calculation, the solid reserve of debris is about 90× 104m3, which provides the material source conditions for the formation of debris flow.
Donggou has a good landform, a good condition for debris source fixation and a good vegetation development in the valley. Debris flow is easy to form under the action of heavy rain. According to the survey, the debris flow is small.
2. Sigou Debris Flow
Sigou is a tributary of the left bank of Yu He River, located in the north of Baoquan Village. The upstream is surrounded by mountains on three sides and exits on one side. This valley is V-shaped. The catchment area of the basin is 2km2, the length of the basin is about 2km, the slope of the basin is 30, and the longitudinal slope of the basin drops to 13%. The above landform conditions are also conducive to the formation of debris flow.
The overburden of Sigou Valley is composed of slope proluvial, and its lithology is mainly gravel, block stone and sub-clay, which is loose or semi-cemented. The thickness of valley bottom overburden is 0 ~ 13m, and the thickness of valley slope overburden is 0 ~ 5m. According to the investigation and calculation, the solid reserve of debris is about 30× 104m3, which provides the material source conditions for the formation of debris flow.
Sigou landform and clastic solid source conditions are good, and vegetation is well developed. Debris flow is easy to form under the action of heavy rain. According to the survey, the debris flow is small.
2 Geological hazard risk assessment
2. 1 collapse disaster
The site collapse disaster mainly occurs on the steep cliff formed by limestone and shallow metamorphic sandstone. Collapse bodies are accumulated in the valley slope zone. Under the current conditions, it is in a stable state and the danger is not great. In the process of engineering construction, under the action of induced factors such as construction disturbance or blasting vibration, dangerous rocks are easy to lose stability and form geological disasters of collapse, with moderate risk; It may also affect the stability of the original collapse body, make it unstable again, and cause collapse disaster with moderate risk; It is also possible to change the stability of the original slope and form a collapse with moderate risk.
2.2 Landslide disaster
According to the Special Report on Stability Analysis of Guishan Landslide of Baoquan Pumped Storage Power Station in Henan Province, the risk assessment of Guishan Landslide is as follows. From the qualitative analysis:
(1) The surface of the sliding body and some sliding zone materials have been cemented, and no new cutting surface running through the whole sliding body has been found;
(2) The slip body was formed in the Middle Pleistocene and the Late Pleistocene;
(3) In the geological history from 65.438 0.4 billion years to 26.5438 0.5 billion years, Guishan landslide has withstood the test of countless ancient earthquakes.
From the quantitative analysis, the overall stability coefficient of sliding body in natural state is 1.27 ~ 1.53.
Therefore, the Guishan landslide is in a stable state, causing no loss and less danger.
However, the storage of water in the upper reservoir of Baoquan Pumped Storage Power Station in Henan Province will affect the stability of Guishan landslide. The water level of the upper reservoir is 758 ~ 790 m, while the elevation of the bottom sliding surface of Guishan landslide is 630 ~ 800 m, and most of the bottom sliding surfaces are below the water level of the upper reservoir. The upper reservoir is close to Guishan landslide (about 1.4km). After the upper reservoir is filled with water, the sliding surface at the bottom of Guishan landslide will reduce the stability of the landslide under the action of long-term infiltration and runoff of reservoir water. In addition, under the action of blasting vibration and other factors, the stability of landslide will also be affected. According to the Special Report on Stability Analysis of Guishan Landslide in Baoquan Pumped Storage Power Station of Henan Province, the stability coefficient of Guishan Landslide is 1.27 ~ 1.53 in natural state, and the landslide is in a stable state. However, under the condition of earthquake intensity above 7 degrees, when the earthquake coefficient k=0. 12, its stability coefficient is 0.92 ~ 65433. Under the direct threat of reservoir engineering safety, the danger is even greater.
2.3 Debris flow disaster
1. Danger of debris flow in Donggou
Under the current conditions, Donggou has topographic conditions and solid debris source conditions, and the vegetation is well developed. Under the action of heavy rain, debris flow is easy to form, and the occurrence degree is moderate. According to records and interviews, a major mudslide occurred in the summer of 1996. Debris flow destroyed a small amount of farmland during the rainstorm, causing no other losses and little harm. Therefore, the risk of debris flow disaster in Donggou is small.
The possibility of engineering construction inducing and aggravating debris flow is mainly manifested in the following two aspects: first, the engineering construction part changes the natural stability of the ditch cover and increases the possibility of solid source migration; Second, a large amount of waste slag produced by engineering construction will become a potential source of debris flow.
The large-scale projects in Donggou and Sheung Shui reservoir areas, as well as the large-scale slope excavation and slag disposal, provide abundant loose material sources for the debris flow in Donggou, so the project construction in Sheung Shui reservoir area may aggravate the debris flow disaster and the risk is moderate.
2. Danger of Sigou Debris Flow
Sigou landform and clastic solid source conditions are good, and vegetation is well developed. Under the action of rainstorm, it is easy to form debris flow, and the occurrence degree is relatively light. According to the investigation, the debris flow in Sigou is small in scale, which has not caused the loss of life and property of residents for many years and has little harm. Therefore, the risk of debris flow disaster in Sigou is small.
There is no engineering construction in Sigou, which has no influence on the debris flow in Sigou and is less dangerous.
3 Prevention and control measures
The prevention and control of geological disasters should implement the principle of "prevention first, combining prevention with control", protect the geological environment and avoid or reduce the loss of geological disasters. In view of the geological disasters such as collapse, landslide and debris flow in the evaluation area, the corresponding prevention measures and suggestions are put forward respectively.
3. 1 Precautionary measures for collapse disaster
Dangerous stones harmful to the reservoir bank should be removed or reinforced.
In the collapse distribution area, the excavation should be carried out in strict accordance with the requirements of relevant codes to avoid slope instability and collapse disaster. Avoidance measures should be taken when necessary.
In case of bank collapse caused by reservoir impoundment project, corresponding protective measures shall be taken in accordance with relevant specifications to avoid the occurrence of collapse disaster.
3.2 Landslide disaster prevention measures
During the excavation of this project, the construction shall be carried out in strict accordance with the requirements of relevant codes to avoid slope instability and landslide disaster.
In view of the landslide caused by the instability of the reservoir bank caused by the reservoir impoundment project, corresponding protective measures should be taken according to the relevant specifications to avoid the occurrence of landslide disasters.
According to the characteristics of Guishan landslide, combined with engineering, topography, stratigraphic lithology and other characteristics. Under the condition of earthquake, it is advisable to take preventive measures of excavation and unloading to improve the stability of landslide. The excavated stone can be used as the filling material of the dam body of the power station reservoir, and the excavation unloading method adopts the contour excavation scheme from top to bottom layer by layer to avoid inducing landslide instability. This preventive measure not only ensures the stability of the Guishan landslide, but also provides filling materials for the dam body of the power station reservoir. This is a scientific, safe and economical landslide prevention measure. According to Supplementary Report on Feasibility Study of Baoquan Pumped-storage Power Station in Henan Province, some tests have confirmed that the landslide is in a stable state from 900m elevation to 800m elevation after excavation and unloading.
3.3 Prevention and control measures of debris flow disaster
Engineering construction will produce a lot of waste slag, and the location of waste slag yard should be reasonable. The construction of waste dump should take corresponding engineering measures according to relevant specifications to prevent debris flow in Donggou River and Yu He River.
For Donggou debris flow and Sigou debris flow, measures such as building sand dams and expanding vegetation coverage should be taken to avoid the occurrence of debris flow disasters. It is suggested to relocate Baoquan village within the scope of debris flow to avoid the loss of people's lives and property.