Trend prediction of geological disasters in Shanxi Province

(Shanxi Geological Environment Monitoring Center, Taiyuan, 030024)

This paper analyzes the geological disasters caused by natural factors and human activities in Shanxi Province. In view of the fact that the change of hydrodynamic conditions is an important factor affecting the change of natural geological disasters, the development trend of natural geological disasters is predicted according to the change of precipitation in the next 13 years. According to the overall planning of mineral resources development, highway traffic development planning and water resources development and utilization planning, the development trend of landslides, mudslides, land subsidence, ground fissures and land subsidence caused by engineering activities is predicted.

Keywords Shanxi geological disaster trend forecast

Geological disasters refer to all kinds of disasters related to geological processes that cause damage to people's lives and property. Geological disasters can be divided into natural geological disasters and geological disasters caused by human activities according to their dynamic conditions. Shanxi is located in the plateau, with large terrain elevation difference, complex geological conditions and concentrated precipitation, and the dynamic conditions for the formation of geological disasters such as collapse, landslide, debris flow and ground fissures are sufficient. It is a natural geological disaster-prone area, and natural geological disasters have the characteristics of many points and wide areas in history. Shanxi is a big province of mining development. With the increase of mining depth and breadth, man-made geological disasters such as ground fissure, ground subsidence, collapse, landslide and debris flow caused by mining frequently occur in this province, resulting in serious economic losses and casualties. In addition, the construction of railways and highways in Shanxi and the centralized over-exploitation of groundwater near important cities have also induced man-made geological disasters to some extent, such as collapse, landslide, ground fissures and land subsidence. According to incomplete statistics, since 1980s, the direct economic losses caused by various geological disasters in Shanxi have reached 654.38 billion yuan, and more than 2,000 people have died. The number of people and property threatened by potential geological disasters is staggering. In recent years, although the relevant departments of Shanxi Province have done a lot of work in the prevention and control of natural and man-made geological disasters, and achieved certain results, due to the variety and wide distribution of geological disasters, geological disasters are still an important factor affecting the safety of people's lives and property in Shanxi Province and hindering the development of the national economy in the province. The genetic mechanism, disaster-causing law and distribution of various geological disasters have not been fully ascertained. Preventing and mitigating geological disasters has become an important practical problem facing Shanxi Province. It is urgent to effectively protect and rationally develop and utilize the geological environment and prevent geological disasters.

According to the dynamic conditions of disaster formation, geological disasters in Shanxi Province can be divided into two categories: geological disasters caused by natural factors and geological disasters caused by human activities. Under the same geological environment, the change of disaster-causing dynamic conditions is the decisive factor to determine the trend of natural geological disasters, while human engineering activities and waste accumulation are the decisive factors for the development and change of man-made geological disasters. On this basis, the development trend of natural and man-made geological disasters in the whole province is qualitatively predicted.

1 prediction of natural geological disasters in Shanxi province

The disasters caused by natural geological processes in Shanxi mainly include collapse, landslide, debris flow, tectonic ground fissures and collapsible ground fissures in loess. From the economic losses and casualties caused by natural geological disasters, collapse, landslide and debris flow are the main disaster-causing bodies, followed by tectonic ground fissures. The economic loss caused by collapsible ground fissures in loess is relatively small, and there is no record of casualties.

The formation of natural geological disasters must have certain topographic and geomorphological conditions, stratigraphic and lithologic conditions, geological structural conditions and hydrodynamic conditions. Among the above conditions, topography, stratum lithology and geological structure conditions are the basic conditions for geological disasters in any area where natural geological disasters are relatively developed, and their changes are slow, but the hydrodynamic conditions change with the different precipitation intensity. Therefore, the change of hydrodynamic conditions plays a very important role in the development trend of natural geological disasters.

The study of natural geological disasters in Shanxi Province shows that there is a very significant positive correlation between debris flow, landslide and collapse and precipitation, and these geological disasters are most likely to occur in the year of sudden rainstorm after years of continuous Mao Mao rain or heavy precipitation. Collapsible ground fissures in loess also have obvious positive correlation with precipitation, and these geological disasters are most likely to occur after heavy rain. Taking Yuanping City as an example, in the investigation and zoning of geological disasters in 200 1, there were eight landslide geological disasters in this area in the 1990s, and the formation time of these eight landslide geological disasters was concentrated in June, July and August of 1995(2 cases) and 1996(6 cases) respectively. Looking up the precipitation data of Yuanping city over the years, the average precipitation for many years (1954 ~ 2000) is 436 mm, the precipitation for 1990 ~ 2000 is 250 ~ 700 mm, and the precipitation for1995 ~11996 is 600 ~ 700 mm The catastrophic geological disaster of debris flow in Taiyuan1August 4, 1996 was also caused by the once-in-a-century rainstorm in Xishan and Gujiao mining areas in the upper reaches of Taiyuan.

Shanxi lies inland on the east coast of the mainland. Surrounded by mountains, the outer edge is influenced by sea breeze, forming a strong continental climate. At the same time, due to the attack of cold air mass in Inner Mongolia in winter, the north is relatively cold, forming the climatic characteristics of Shanxi, such as long winter, cold and dry, less precipitation, short summer, hot and rainy, large daily temperature difference in spring, heavy sandstorm, severe drought, short autumn and mild climate. The climate type of Shanxi province belongs to temperate continental climate, with obvious changes in four seasons and great differences between north and south. The average annual precipitation in the whole province is between 400 ~ 650 mm. Among the total annual precipitation, it accounts for 15% ~ 20% in spring, 50% ~ 75% in summer, 0/5% ~ 30% in autumn and 2% ~ 3% in winter. Precipitation is highly concentrated from July to September every year. The distribution of annual precipitation in the whole province has the characteristics of decreasing from southeast to northwest, and mountainous areas account for more than 20% of the basin. The precipitation in Shanxi Province changes greatly every year, and there is often a phenomenon of continuous rain and drought. Precipitation has a period of 10 ~ 13 years. The precipitation in Shanxi from 1990s to now is a dry year, which is about 2.8% less than that in 1980s. After entering 2 1 century, with the end of the drought and precipitation cycle in the last decade, Shanxi will enter a rainy and precipitation cycle in the next 13 years, and the precipitation will increase obviously compared with the previous decade. Under the influence of increased precipitation and enhanced hydrodynamic conditions, the frequency of natural geological disasters in Shanxi will gradually increase with the change of precipitation in the next 13 years. However, in recent years, Shanxi Province has intensified the propaganda and prevention of geological disasters, and the people's awareness of disaster prevention and mitigation in disaster-stricken areas and hidden danger areas has been significantly enhanced. Although the frequency of natural geological disasters will gradually increase, the economic losses and casualties caused by natural geological disasters will be effectively controlled.

2 Shanxi man-made geological disaster trend prediction

Disasters such as collapse, landslide, debris flow, cracks in mined-out areas and ground collapse caused by human engineering activities in Shanxi Province mainly include mining, cutting and building cutting. Excessive pumping of groundwater in industrial and mining enterprises and urban residents will induce man-made geological disasters such as land subsidence and ground fissures. Judging from the economic losses and casualties caused by man-made geological disasters, goaf cracks, goaf ground collapse, mining landslide and mining collapse are the main disaster-causing bodies, and the economic losses caused by ground subsidence and ground cracks caused by excessive pumping of groundwater are also great. However, the economic losses and casualties caused by geological disasters such as cutting and building cutting are relatively small.

The type and intensity of man-made geological disasters induced by human engineering activities are closely related to the national economic development level and national industrial policy at that time. In the 1970s and 1980s, when the economic development level was low, there were many small and medium-sized mines in Shanxi, and the construction of county and township highways and national first-and second-class highways flourished. Geological disasters such as collapse, landslide, ground fissure, land subsidence and debris flow induced by human engineering activities have the characteristics of wide range, high frequency and large accumulated losses. After entering the 1990s, highway construction entered the era of expressway. Because of the high requirements for site selection, survey, design, construction and prevention of geological disasters in expressway construction, the geological disasters caused by road construction and slope cutting are obviously reduced. At present, there is no record of man-made landslide or man-made geological disaster damage caused by expressway construction in Shanxi Province. Since 1990s, coal mining in Shanxi Province has entered a period of standardized development. The administrative department shut down and destroyed a large number of illegal small coal mines, which fundamentally improved the mining order in Shanxi. Man-made geological disasters, such as ground collapse and house damage caused by unauthorized excavation and cross-border mining, have been obviously controlled, and mine geological disasters, mainly coal mining, have changed from sudden and random before treatment to frequent occurrences within people's control and prediction. The losses caused by man-made geological disasters induced by mining are obviously reduced.

According to the highway traffic development plan and the overall planning of mineral resources in Shanxi Province, during the planning period of 13, highway traffic construction in Shanxi Province will still focus on highway construction, and it is estimated that man-made geological disasters induced by highway construction are slight, far less than those induced by low-grade highway construction.

Judging from the overall planning of mineral resources, the short-term planning objectives of Shanxi Province in 2005 are: the total amount of mineral resources development and utilization is effectively controlled, and the total amount of coal mining is controlled at about 300 million t; Adjust and optimize the mining structure and layout, the coal industry will change from quantity to quality and benefit, from producing primary products to comprehensive development and utilization, improve the overall quality, consolidate the position of coal industrial base, and form three major coal group companies; Continue to close small coal mines that are illegally exploited, have low recovery rate, threaten the safety of large mines, do not have safe production conditions, destroy the ecological environment and cause serious pollution, so as to reduce the number of coal mines in the province to less than 3,000; Adjust the scale structure of mines to form a pattern of coordinated development with large and medium-sized mines as the backbone; The development and utilization mode of mineral resources has initially changed from extensive to intensive, the utilization efficiency has been obviously improved, and indiscriminate mining and destructive mining have basically been put an end to; The mining scale of newly-built mines basically adapts to the scale of deposit reserves, and the recovery rate of coal resources mines is obviously improved; The ecological environment of mines has been initially improved, and the supervision and management of mine environment have been strengthened. No new mining projects with irreparable damage to the ecological environment will be built, and the deposit system for prevention and control of geological disasters will be implemented in the development of mineral resources. The incidence of secondary geological disasters in mines has obviously decreased, the treatment rate of "three wastes" in mines has obviously increased, the recovery and treatment rate of mine ecological environment has reached 20%, and the land reclamation area of mines has increased by 6,543,800 hectares. The long-term goal of the province in 20 10 is to further intensify the reform and opening-up in the field of mineral resources exploration and development, initially realize the fundamental transformation of mineral resources utilization and management methods, and basically form a competitive new mining economic system that meets the requirements of the socialist market economy and focuses on scale operation. The structure and layout of mineral resources development and utilization were further adjusted and improved, the efficiency of resource utilization was further improved, the development of mineral resources and ecological environment protection were coordinated, and the mining ecological environment was further improved. Judging from the above short-term and long-term planning objectives, under the principle of keeping the total amount basically unchanged, Shanxi's mining development will gradually realize the substitution of large for small, form a new mining economic system with large-scale operation as the main body, and maintain the coordinated development of mining development and environmental protection. At the same time, in the overall planning of mineral resources in Shanxi Province, according to the principles of corresponding laws and regulations, relevant planning, safeguarding national strategic interests and following natural and economic laws, the mineral resources in Shanxi Province are divided into four categories: encouraged mining areas, restricted mining areas, prohibited mining areas and protected mining areas. From the perspective of mining layout, with the gradual depletion of coal resources in major mining areas such as Datong, Yangquan, Fenxi and Taiyuan Xishan, Shouyang in the north wing of Qinshui coalfield and Liulin, Baode, Hequ and Pianguan in Hedong coalfield have become the second battlefields opened by Shanxi Coal Army, and a number of large and medium-sized mines with an annual output of 600,000 ~ 3 million tons are being built in these areas. Some of them are planned to have an annual output of 9 million tons (Shanxi can predict that with the continuous production of these large and medium-sized mines, the geological environment conditions in the above areas will deteriorate sharply, and man-made geological disasters such as ground fissures, ground subsidence, mining collapse, mining landslide and water resources destruction will occur in large numbers. Therefore, during the planning period, in addition to geological disasters caused by coal mining in Datong, Shuozhou, Xuangang, Taiyuan Xishan, Yangquan, Fenxi, Xiaoyi, Huozhou, Lu 'an, Changzhi and Jincheng, the above-mentioned new mining areas will also induce many geological disasters in the future. Man-made geological disasters induced by mining in Shanxi Province are on the rise. However, due to the strict production planning and environmental protection planning of these large mines, the man-made geological disasters induced by them are inevitable geological disasters in the mine production process, which can be predicted and planned, and the losses caused are relatively small.

With the sustained and rapid development of mining industry, the discharge of mining waste in Shanxi Province has increased year by year, and there are more and more dumping sites. According to the Report on Investigation and Remediation of Mine Tailings, Solid Waste, Land Reclamation and Geological Environment Protection in Some Areas of Shanxi Province, the discharge of mine tailings and solid waste in some areas of Shanxi Province is as follows (table 1) and (table 2):

Table 1 Statistics of tailings discharge from some mines in Shanxi Province

Table 2 Discharge Table of Solid Waste in Main Mining Areas of Shanxi Province

In addition, driven by the national coal industry policy and the western development policy, a large number of large-scale coal-fired power plants have been built in Shanxi Province in recent years. The scale of the first phase project is 600- 1200mw, and the annual ash discharge of each coal-fired power plant is 350,000-700,000 m3. According to the estimation of the number of existing and under construction coal-fired power plants in the province, the total annual ash discharge of coal-fired power plants in the province is1more than 0 million m3. These mine tailings, solid wastes and power plant ash are huge and widely distributed, and most of them are distributed in valleys, which constitute an important source of geological disasters of mudslides in Shanxi Province. Under the condition of rainstorm, these substances are easily washed out of the valley, forming a geological disaster of debris flow. Therefore, during the planning period, the danger of geological disasters caused by human engineering activities in Shanxi is increasing.

According to the investigation, Jianshan Iron Mine in loufan county, Taiyuan, Pingshuo Open-pit Mine in Shuozhou, Zhongtiaoshan Nonferrous Metals Company in Yuncheng, Xishan Mining Area in Taiyuan, Dongshan Quarry in Taiyuan, etc. Geological disasters caused by human factors may occur during the planning period. Once these debris flow geological disasters occur, the economic losses and casualties will be very serious.

Man-made geological disasters such as ground subsidence and ground fissures induced by groundwater overexploitation in Shanxi are mainly distributed in large and medium-sized cities with dense population and concentrated industrial and mining enterprises, such as Taiyuan, Datong, Linfen and Yuci. Among them, Taiyuan has the earliest land subsidence time, the largest affected area and subsidence, and the largest economic loss. The land subsidence in Taiyuan City is caused by excessive pumping of groundwater, and the range of land subsidence is in good agreement with the range of shallow and deep groundwater drop funnels. Once the land subsidence disaster is formed, it is difficult to recover under the existing economic and technical conditions, and the main prevention goal can only be to control the scope and amount of subsidence. According to the planning of Shanxi Provincial Water Resources Department, the design water supply capacity of the South Main Line of Taiyuan Yellow River Diversion Project and the Yellow River Diversion Water Supply Project is determined according to the sum of water shortage and groundwater overexploitation in Taiyuan water supply area, plus the increased water demand of urban development. Therefore, while the new water source of the Yellow River Diversion Project is flowing, Taiyuan will close some groundwater exploitation wells according to the overexploitation of different groundwater units, so as to reverse the overexploitation of groundwater in the water supply area, realize a virtuous circle, meet the sustainable development of the ecological environment and groundwater resources, and ensure the long-term stable operation of the Yellow River Diversion Project. At present, the proposed regulation scheme is as follows: after the Yellow River diversion for water supply in 2003, the annual exploitation of key water users will be reduced from 273.35 million m3 to184.07 million m3, and the exploitation of compressed groundwater will be 88.03 million m3/a, accounting for 82% of the over-exploitation, including 49.52 million m3 of pore water and 37.43 million m3 of karst water. Coupled with the regulation of decentralized water users, the over-exploitation of groundwater in Taiyuan will be effectively controlled and the balance between groundwater exploitation and compensation will be basically realized. By 2005, when the water supply of the Yellow River Diversion Project is increased to 800,000 m3/d and the exploitation is reduced to 43.09 million m3/a, the groundwater in the control area will be restored and enter a virtuous circle. After the Yellow River water in Shuozhou City, Datong City, the north trunk line of the Yellow River Diversion Project began to supply water, the groundwater protection scheme was similar to Taiyuan. In Yuncheng, another seriously over-exploited area, combined with the completion, supporting and water supply of Yumenkou, Zuncun Yellow River Project and Langdian Water Source Project, the industrial and agricultural groundwater exploitation in this area was reduced to 80 million m3/a, accounting for 56% of the over-exploitation in this area, and the Yellow River water was used instead. Therefore, during the planning period, the land subsidence disasters in Shanxi's big cities, mainly Taiyuan and Datong, will be controlled, but with the improvement of urbanization level, the rapid development of industry and agriculture and the sharp increase of water consumption in small and medium-sized cities, the original land subsidence disasters may aggravate or appear new small-scale land subsidence and ground fissure geological disasters.