(1 Geological Environment Monitoring Institute of Xinjiang Uygur Autonomous Region, Xinjiang, 830000; 2 China Geo University 200 1 Master's class is studying, Beijing, 100083).
The complex geological environment and fragile ecological environment in Urumqi, coupled with frequent engineering activities such as human coal mining, have caused serious ground collapse, collapse, landslide and debris flow disasters in this area, and their distribution has certain laws. Based on the principle of giving priority to prevention and combining avoidance with prevention, measures such as monitoring and forecasting, avoidance, project management and comprehensive planning of project construction layout are taken to prevent and control the above disasters in a planned and step-by-step manner, so as to achieve the purpose of disaster prevention and mitigation.
Keywords: prevention and control of sudden geological disasters in Urumqi
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Urumqi is located at the northern foot of Tianshan Mountain, on the southern edge of Junggar Basin, surrounded by mountains on three sides, with Bogda Mountain in the northeast and Tianshan Mountain in the south. Urumqi is surrounded on three sides from northeast to southwest, and only the northwest plain borders changji city and Miquan City. Among them, the area of high mountains and low mountains accounts for 53. 1%, the area of low mountains and hills accounts for 20.6%, and the area of plains only accounts for 26.2%.
Urumqi is located in the compound part of Tianshan geosyncline fold belt and Junggar depression. The tectonic and neotectonic movements in this area are strong, faults and folds are developed, landform types are complex, strata lithology changes greatly, and geological environment is fragile. The mountains are high and steep, and valleys are developed, forming steep slopes, cliffs, deep valleys, pedestal terraces and other landforms. Structure and weathering make joints and fissures in rock strata develop and rock mass break, which provides basic conditions for the occurrence of collapse, landslide and debris flow. The rainfall in this area is not very large, but it is concentrated and heavy. In addition, human activities make collapses, landslides and mudslides happen frequently. The area is rich in coal resources, and the ground collapse disaster caused by human coal mining activities is also very serious.
With the acceleration of economic development, the intensity and scope of human engineering activities are getting larger and larger, and the damage to the geological environment will become more and more serious, resulting in more and more geological disasters and increasing losses and threats to human life and property. The prevention and control of geological disasters has become one of the main tasks facing people at present.
1 Types, distribution and hazards of sudden geological disasters
According to the results of investigation and zoning of geological disasters in Urumqi completed by Geological Environment Monitoring Institute of Xinjiang Uygur Autonomous Region in 200 1, there are a total of sudden geological disasters in Urumqi 159, including ground collapse 102, collapse 20, landslide 14 and debris flow 23. 159 geological disasters, 97 have occurred and 62 are potential points, all of which are hidden dangers.
1. 1 ground collapse
Ground collapse is mainly caused by roof caving after coal mining (10 1), followed by roof caving in civil air defense projects (1). The ground subsidence area of the city is 4.85km2, with small-scale (7 1) subsidence as the main factor, followed by medium-sized (8) and large-scale (2).
The distribution of land subsidence is closely related to the distribution of coal seams. Jurassic coal-bearing strata are distributed in Hongguangshan-Lucaogou, northeastern margin of Chaiwobao basin, Xishan area, Xia Hou basin and Aiweiergou area. After years of mining, a large area of mined-out area has been formed. Under the action of artificial caving, blasting vibration, earthquake or rainfall, the infiltration of snowmelt water and the gradual destruction of security coal pillars, the surface rock and soil collapsed, leading to ground collapse. On the surface, there are mainly two forms: beaded circular collapse pit and long strip collapse ditch. The diameter of the collapse pit is generally 10 ~ 20m, the maximum is 30m, and the depth is 5 ~ 15m. The width of the subsidence ditch ranges from less than 1m to 120m, and the depth ranges from less than 1m to 40m.
The hazards of ground collapse mainly include: ① endangering or threatening people, vehicles and animals that have strayed into mined-out areas; (2) destroying the original ecological environment; (3) destroying farmland and groundwater system, resulting in dry wells, shallow wells and leakage irrigation; (4) A large number of unconsolidated underground mined-out areas bring great inconvenience and hidden dangers to the ground construction and affect the development of urban construction; ⑤ Causes uneven settlement or crack of building foundation. For example, in March of 1972, Xiaohonggou in Dongshan District was flooded, and people were fighting flood above the goaf of coal mine, and suddenly the ground collapsed, causing 27 deaths.
According to records and statistics, land subsidence has caused 33 deaths and 2 injuries, resulting in a direct economic loss of 2,083,200 yuan.
1.2 crash
Collapse is divided into two forms: bedrock collapse (8 places) and Quaternary accumulation collapse (collapse) (12 places). The collapse is mainly small (19), and only 1 bedrock collapse is moderate.
Affected by folds and fault structures, rock masses in bedrock mountain areas are broken, and bedrock collapses can be seen everywhere on steep slopes, but the scale is not large, and the mountainous areas are generally sparsely populated, so the possibility of disasters is low. In human engineering economic activity areas, such as mines, mountain roads, grazing roads, etc. They are vulnerable to the danger of collapse. In several isolated low mountain residual hills in the central city (such as Hongshan and Pingdingshan), the slopes often collapse and sink due to the narrow mountain range, steep slopes, developed joints and cracks, and prominent dangerous rock masses. When the collapse occurred, stones of different sizes quickly rolled down and formed a pile at the foot of the slope.
The collapse of accumulation layer is mainly distributed in high-order land and high-steep slope, which is characterized by loose scarps or cliffs on the slope. Collapse mainly occurs at the foot of the slope, which forms a loose accumulation cone. The scale of collapse is small, but the scarp or toe of slope is often inhabited, which is easy to form disaster events.
The main hazards of collapse are: threatening the safety of life and property of residents at the foot of the slope, destroying and blocking roads, and damaging vehicles and engineering facilities at the foot of the slope. For example, the dangerous slope in Heishantou, Pingdingshan, is abrupt at the top and easy to collapse, posing a serious threat to the residents at the foot of the slope.
The 20 collapses in Urumqi did not cause casualties or property losses.
1.3 landslide
Landslides in this area are undeveloped, mainly soil (loose accumulation layer) landslides (1 1), followed by bedrock landslides (3). Small in scale.
Soil landslides mostly occur on steep slopes and scarps in low-middle mountain and hilly areas. The sliding body is a loose accumulation of residual slope deposits, mainly cohesive soil and gravel soil, with loose structure, small cohesion and strong water permeability, which is obviously different from the lower bedrock, and landslides are prone to occur in the stratum and contact surface. Generally, the scale is small, ranging from ten meters to tens of meters, with the maximum not exceeding 100 meters and the thickness of 1 ~ 3m. The occurrence of landslide has the nature of sliding first and then sliding.
There are three bedrock landslides in the area: one is Heijiashan landslide; Secondly, the coal mining face landslide in Miaoergou village of Shuixigou township, both of which are closely related to artificial quarrying and coal mining engineering activities; The third is the landslide at the natural steep slope on the east bank of the upper reaches of Toutun River.
The hazards of landslide are firstly burying and destroying residential areas and buildings at the foot of slope, causing casualties and property losses; The second is to block roads and destroy canals. For example, 1984, 1990, 1996, landslides occurred in the east, west and middle parts of the south side of Heijiashan in turn, resulting in two deaths, and 17 houses collapsed, resulting in economic losses of more than 654.38 million yuan. At present, landslides in the middle and west sections still threaten 65,438 people living at the foot of the slope of Heijia Mountain.
Landslides in the jurisdiction have caused four deaths and direct economic losses of 4,065,438+10,000 yuan.
1.4 Debris Flow
Debris flow in this area belongs to gully debris flow. The scale is mainly small (18), followed by medium (5).
Debris flow formation areas are mostly confined to the mountainous areas with medium and low bedrock at an altitude of 1000 ~ 2500 m, mainly in Aragou area, the seat of the former Nanshan mining area government, and Xiaoshagou, Daxigou and Gangou in Dabancheng in front of Nanshan Mountain. Gullies are developed in this area, and the longitudinal slope of the gully bed is large, which has the topographic conditions to form debris flow gullies. At the same time, the bedrock is exposed, with strong weathering and crushing, and the surface vegetation coverage rate is low. There are a lot of loose debris in the slope, toe and trench bed. Debris flow can occur during heavy rain or heavy rain, mostly in June-September when heavy rain is concentrated.
The damage caused by debris flow mainly occurs in the accumulation area, and most of it is due to people's lack of judgment on debris flow ditch and its harm, and they misoperation in the disaster risk area, becoming victims or threats of disasters, causing great losses. The main failure modes of debris flow are: ① siltation hazard. It can destroy the facilities in the accumulation area and bury them. For example, on August 4th 1995, the debris flow in Nanshan mining area buried factories, workshops, warehouses, office buildings, shops and other buildings, covering an area of 2000m2, and the direct economic loss was128.04 million yuan; (2) Wash away. Debris flow has the characteristics of fast arrival, fast velocity and large energy, so it has great scouring and impact ability, which directly threatens the safety of engineering facilities and people's lives and property in the downstream area of debris flow. For example, on June 24th 1988, a sudden mudslide occurred at the location of Dongfeng Machinery Factory in Nanshan Mining Area, which destroyed 6422m2 of various factories, warehouses, offices, houses and other areas, resulting in a direct economic loss of 6,077,800 yuan. ③ Danger of blockage. Most roads in mountainous areas are built along the river. When debris flow occurs on both sides of the valley, it is easy to be washed away or blocked, resulting in traffic jams. In addition, the occurrence of debris flow will also cause the blockage and destruction of water diversion channels and the blockage of rivers and ditches. During the period of 1997, the debris flow occurred for the first time in Daxigou Youth Canal, which destroyed the silted diversion canal by 0.8km and the flood discharge canal by 0.5km, resulting in a direct economic loss of 2.8 million yuan.
To sum up, the distribution of sudden geological disasters in Urumqi has obvious laws. Collapse and debris flow are mainly distributed in the eastern and southern bedrock mountainous areas, followed by ground collapse and landslide, and debris flow is the most harmful. The low mountains are dominated by ground collapse, followed by collapse and landslide; Sudden geological disasters in plain areas are not developed.
All kinds of sudden geological disasters occurred in Urumqi, causing 37 deaths and 2 injuries, and the direct economic loss was 25 195200 yuan. It is predicted that the threatened population is 2524, which may cause direct economic losses of 90.07 million yuan within the disaster area.
2. Prevention and control plan for sudden geological disasters
2. 1 control principle
(1) Highlight the principle of "people-oriented". Put people's life safety in the first place, and minimize casualties and property losses caused by sudden geological disasters. Further popularize the knowledge of geological disaster prevention and control, and improve the public's awareness and ability of disaster prevention and mitigation.
(2) Adhere to the principle of "prevention first, combining avoidance with treatment". Actively adopt forecasting and early warning to prevent sudden geological disasters, especially those induced by human beings. Give full play to the leading role of governments at all levels, mobilize the enthusiasm of society and the general public, adjust measures to local conditions, pay attention to reasonable avoidance, and choose key governance.
(3) adhere to the principle of overall planning, highlighting key points and implementing them step by step. According to the distribution law, development characteristics, danger and harm degree of sudden geological disasters, combined with the local economic level and development planning, the prevention and control areas of light, heavy, slow and urgent are divided, and the prevention and control of sudden geological disasters are implemented respectively, so as to combine the short-term with the long-term and focus on local environmental improvement.
(4) Adhere to the principle of combining engineering governance with non-engineering governance. On the premise of giving priority to prevention, supplemented by avoidance, the hidden danger points of sudden geological disasters that are particularly harmful will be treated by engineering, and the monitoring and emergency system and information system of sudden geological disasters will be further improved, so that passive emergency avoidance will become active disaster reduction and prevention, and the prevention and control of sudden geological disasters will achieve a virtuous circle.
(five) the implementation of the "Regulations on the Prevention and Control of Geological Disasters" stipulates that geological disasters caused by natural acts shall be governed by the government, and the beneficiaries shall bear reasonable burdens; Man-made geological disasters are the responsibility of the responsible person.
2.2 Prevention and Control Plan
2.2. 1 monitoring and forecasting scheme
Monitoring and forecasting is one of the important means to prevent sudden geological disasters. Using the monitoring network system, fully mobilize the masses, through the combination of professional monitoring and mass monitoring, the implementation of sudden geological disasters monitoring and forecasting.
According to the characteristics of sudden geological disasters in Urumqi, the following simple methods can be adopted:
1. Ground collapse
(1) Macro-geological survey method: manual investigation and monitoring of subtle changes in surface cracks and collapses.
(2) Monitor and record the change of goaf in time.
2. Collapse and landslide
(1) Monitoring of ground deformation and displacement: set up stable and fixed detection control points around the landslide area, set up monitoring points in the landslide area, and measure the displacement change dynamics of the monitoring points by line of sight method.
(2) Monitoring the relative displacement of cracks: set monitoring points on both sides of cracks between the landslide body and the landslide body, as well as on both sides of cracks in the side walls, retaining walls and mortar rubble ditches of the affected houses to measure the changes of cracks, or stick cement mortar sheets and paper on the cracks to observe the changes of cracks.
(3) Macro-geological survey, in which various subtle changes in the landslide area are investigated and monitored by manual daily patrol.
3. Debris flow
The key to monitoring debris flow in this area is to monitor rainfall (rainstorm), which can be monitored by setting fixed rainfall monitoring stations and temporary rainfall monitoring points.
The above monitoring results should be reported to the superior in time, so as to sort out and analyze and make accurate and timely forecasts.
2.2.2 Avoidance plan
For most sudden geological disasters in Urumqi, avoidance is the best choice. For example, for the ground collapse disasters in most coal mined-out areas, because the mined-out areas are mostly barren hills, as long as people and vehicles are prohibited from entering, casualties and property losses can be avoided; On the other hand, because there are only bungalows in the foothills of landslides and debris flow gullies, the living conditions are poor and the cost of disaster control is high. In the case of very limited prevention and control funds, compared with the cost of project management, it is necessary to relocate. If the relocation cost is low, choose the right one.
Governance plan
When the avoidance method is not applicable, governance is a disaster prevention countermeasure. Before taking control measures, further engineering investigation must be carried out on the disaster body. According to the different types of sudden geological disasters in Urumqi, the methods adopted are different.
Ground collapse: the underground mined-out area can be forced to collapse and backfilled with the original collapse to restore the ecological environment; In the area of important engineering construction or planning site, grouting is used to eliminate underground goaf.
Collapse and landslide: drainage works (mainly ground drainage and seepage prevention) shall be adopted; Supporting works (anti-slide piles, anti-slide walls, anchorage, etc.). ); Unloading, cleaning and maintenance works; Slope protection, shotcrete and other engineering measures.
Debris flow: Take comprehensive control measures such as monitoring, engineering (drainage), biology and the whole basin.
2.2.4 Reasonable planning of various construction layout schemes.
In the prevention and control of geological disasters, it is one of the important means to rationally plan the layout of various projects and embody the policy of "prevention first". In the past, due to people's lack of sufficient understanding of the occurrence of geological disasters, on the one hand, the destruction of geological environment by engineering construction itself led to the occurrence of disasters, on the other hand, the engineering construction was placed in the dangerous range of geological disasters, which led to the occurrence of disasters and caused casualties and property losses. Therefore, rational planning of the layout of various projects is also one of the important contents of geological disaster prevention and control. Therefore, according to the overall urban planning and land use planning of Urumqi, all kinds of engineering construction layout will be carried out, and the prevention and control of geological disasters will be effectively combined with urban construction planning, mineral development and land overall planning.
According to the requirements of the Notice of the Ministry of Land and Resources on Implementing Geological Hazard Assessment of Construction Land, urban construction, engineering construction in geological hazard-prone areas and other engineering projects that may cause geological disasters must be assessed at the project site selection stage.
In accordance with the principle of "whoever induces and governs", the compilation system of mine geological environment protection scheme and the access system for new mines shall be implemented, the mineral reserve system shall be strictly implemented, the supervision and management of mines shall be strengthened, the safety of people's lives and property shall be guaranteed, the mineral resources shall be protected, the ecological environment shall be protected and restored, and the sustainable development of mining industry shall be promoted.
Strengthen land use management in areas prone to geological disasters, and at the same time rationally plan the layout of various projects to prevent illegal land use of various projects from inducing geological disasters; Avoid improper land use, which leads to the project construction entering the threat range of geological disasters, thus causing disasters.
2.2.5 bioengineering treatment scheme
Bioengineering treatment is undoubtedly one of the important measures in the prevention and control of geological disasters, and the longer the time, the more obvious the effect. However, due to the sudden geological disasters in Urumqi and the constraints of regional physical geography and environmental conditions, it is not suitable for large-scale development at present. We can choose 1 ~ 2 debris flow gully in Alagou area as the pilot to implement bioengineering control measures, and obtain the methods and experiences of bioengineering control of debris flow in arid areas.
Through the full implementation of the prevention and control of sudden geological disasters, the safety of people's lives and property will be guaranteed to the maximum extent, the frequency and loss of geological disasters will be minimized, and the rapid development of social economy will be promoted.