Ground collapse refers to the geological phenomenon that the surface rocks and soil fall downward under the action of natural or man-made factors, forming collapse pits (holes) on the ground. When this phenomenon occurs in areas with human activities, it may become a geological disaster, especially karst collapse.
Second, what harm will the ground collapse cause?
Many cities in China have experienced karst ground collapse. The collapse caused a large number of buildings to collapse, roads to collapse, fields to be destroyed, wells to dry up or be scrapped, and scenic spots to be destroyed, which caused great losses to urban production and construction and people's lives. According to incomplete statistics, the cities with serious karst ground collapse disasters in China include Dalian, Liaoning, Qinhuangdao, Tangshan, Jinan, Tai 'an, Zibo and Zaozhuang, Wuhan, Huangshi and Xianning, Hubei, Huaihua, Loudi, Qiancheng, Xiangtan and Chenzhou, Nanjing, Jiangsu, Hangzhou, Zhejiang, Jiujiang, Yichun, Shanggao, Kunming, Yunnan and Guiyang, Guizhou. Among them, Dalian, Qinhuangdao, Tai 'an, Wuhan, Guilin, Shuicheng and Kunming. It has strong destructive power and great influence, especially the ground collapse in Shuicheng, Guizhou Province. Shuicheng (Liupanshui City) produced 1023 collapse pits within a range of about 5 square kilometers due to the massive pumping of groundwater from the well 16, which caused 89 houses to crack or collapse, roads to collapse, 423 mu of farmland to be destroyed, and telephone poles to collapse, which once caused power failure in the whole city, with direct compensation and economic losses reaching more than 2.6 million yuan. In some areas, sewage injection has caused groundwater pollution and ecological environment deterioration. In addition, the Cuihu Lake in the center of Kunming, Yunnan Province collapsed, which made the water of Cuihu Lake, a scenic spot with a long history, dry up, pavilions collapsed, small bridges and flowing water were destroyed, and the famous spring Kowloon Pool became a sinkhole, and the flowers in the lake withered. full of green.
In underground mining, due to strong drainage and water inrush, karst ground collapses in many mining areas, resulting in cracking and collapse of buildings, destruction of farmland, interruption of roads, delay of mine production, even suspension of production and scrapping, which has great economic losses and social impact. According to incomplete statistics, the direct economic loss of karst ground collapse in China's mining areas has reached more than 40 million to 50 million yuan. According to preliminary investigation data, at present, the large-scale mining areas that have caused karst ground collapse disasters in China are Enkou Coal Mine, Doulishan Coal Mine, Qiaotouhe Coal Mine, Carboniferous Dam Coal Mine, Shuikoushan Lead-zinc Mine, Daye Tonglushan Copper Mine, Daye Yehuaxiang Copper Mine, Daye Daguangshan Iron Mine, Yidu Yi Song Coal Mine, Jiangxi Yufenzhuang Coal Mine, Leping Huating Manganese Mine, Leping Qiaotouqiu Coal Mine and Leping Mingshan Coal Mine. Guangdong Shilu Copper Mine, Fankou Lead-zinc Mine, Yingde Pyrite Mine, Heishigang Pyrite Mine, Yangchun Pyrite Mine, Liaoning Asbestos Mine, Shandong Laiwu Iron Mining Zhuang Mine, Laiwu Gujiatai Iron Mine, Anhui Tongling Xinqiao Copper Mine, Huainan Coal Mine, Tongguanshan Mine, Hebei Tangshan Kailuan Coal Mine and other dozens of mining areas. Among them, the karst ground collapse in Enkou Coal Mine, Shuikoushan Lead-zinc Mine, Fankou Lead-zinc Mine, Yudingshan Lead-zinc Mine and Tonglushan Copper Mine is the most typical and intense.
Karst ground collapse is also one of the main disasters of railway. Over the years, there have been about 52 major collapses of railway lines and stations in China, with the cumulative outage of 1680 hours, and the treatment cost of some work sites has reached hundreds of millions of yuan. Among the main trunk railways in China, Beijing-Guangzhou railway, Guiyang-Kunming railway, Zhejiang-Jiangxi railway, Jinpu railway, Shenyang-Dalian railway and Chongqing-Dalian railway have serious karst ground collapse disasters. Collapse causes station buildings to be destroyed, subgrade to sink, roads to be suspended, bridges and culverts to crack and collapse, tunnel construction to be blocked, railway stops from time to time, and even trains to derail. In some sections, the train runs at a low speed for a long time, causing huge losses. For example, the ground of Nanling tunnel and Dayaoshan tunnel on Beijing-Guangzhou line collapsed, causing the built railway to sink, traffic to be interrupted and tunnel construction to be blocked; Three major landslides occurred successively in K4 13-K606 section of Guiyang-Kunming Railway, which caused two trucks to overturn and stopped running for 7 1 hour, and the treatment investment reached170,000 yuan; The ground subsidence of Tai 'an Station on Jin-Pu Line caused the subgrade to sink, the track was overhead, and the traffic was once interrupted, and the reconstruction cost reached more than 20 million yuan. The ground collapse of Wafangdian urban section of Shenyang-Dalian railway caused the train to stop for 8 hours.
3. What are the types of land subsidence?
1. Karst collapse
Because karst caves exist in soluble rocks (mainly carbonate rocks, followed by gypsum and rock salt, etc. ). In karst areas covered by loose soil layer on karst rocks, the collapse mainly occurs in soil layer, which is called "soil layer collapse", with the largest number of development and the widest distribution; When all kinds of rocks forming the roof of the cave are broken, the "bedrock collapse" of roof collapse will also occur. Karst collapse is widely distributed in China, and it has occurred in 26 provinces (autonomous regions and municipalities directly under the Central Government) except Tianjin, Shanghai, Gansu and Ningxia, among which Guangxi, Hunan, Guizhou, Hubei, Jiangxi, Guangdong, Yunnan, Sichuan, Hebei and Liaoning are the most developed provinces (autonomous regions). According to statistics, the total number of karst collapses in China is 284 1, and there are 33 192 sinkholes, covering an area of about 332 square kilometers, resulting in economic losses of more than 654,380+0.2 billion yuan every year.
2. Non-karst collapse
Collapse caused by non-karst caves, such as goaf collapse, collapse caused by loess caves in loess area, collapse caused by tunnel roof in basalt area, etc. The latter two are limited in distribution. Goaf collapse means that the roof of underground goaf in coal mines and metal mines is easy to fall and collapse, which is widely distributed in China. At present, it has been found in 24 provinces (autonomous regions and municipalities) except Tianjin, Shanghai, Inner Mongolia, Fujian, Hainan and Tibet, among which Heilongjiang, Shanxi, Anhui, Jiangsu and Shandong provinces are more developed. According to incomplete statistics, in 2 1 province (autonomous region and municipality directly under the central government), * * has 182 mined-out collapses, 1592 potholes, and the subsidence area is 1 150 square kilometers, resulting in an annual economic loss of 3/kloc.
Among the above types of collapse, karst collapse has the widest distribution, the largest number, high frequency and the most inducing factors, which is very concealed and sudden and seriously threatens people's lives and property safety.
The plane shapes of karst collapse are round, oval, long and irregular, which are mainly related to the opening shape of karst cave in the underlying rock and the uniformity of the properties of overlying rock and soil on the plane. Its cross-sectional shapes are altar-shaped, well-shaped, funnel-shaped, dish-shaped and irregular, which are mainly related to the nature of the collapsed layer. The collapse of cohesive soil layer is mostly altar or well-shaped, the collapse of sandy soil layer is mostly funnel-shaped, the collapse of loose soil layer is often dish-shaped, and the collapse profile of bedrock is often irregular step-shaped.
The scale of karst collapse is expressed by the size of a single collapse pit, which mainly depends on the development degree of karst, the opening size of karst cave, the thickness of overburden and other factors. According to statistics, the diameter of soil subsidence pits is generally less than 30 meters, most of which are less than 5 meters, reaching 63%~7 1%, 5~ 10% ~ 20%, and some are as high as 60~80 meters. The visible depth of subsidence pits is mostly less than 5 meters, accounting for 84%~97% of the total. The scale of bedrock collapse is generally large. For example, Xiaoyan Bay in Xingwen County, Sichuan Province collapsed, with a length of 650m, a width of 490m and a depth of 208m.
Fourth, the causes of ground collapse
Human activities have played an important role in the formation and development of land subsidence. Unreasonable or excessive human activities may induce or lead to ground collapse. Several human activities that have an important influence on land subsidence and their functions are briefly described as follows.
Underground goaf of mine. Underground mining activities caused a certain range of mined-out areas, which made the upper rock mass lose its support and led to ground collapse. This kind of human activity is the main reason for the ground collapse in the mining area. This kind of ground collapse has occurred in many mining areas in China, causing considerable harm. For example, the ground subsidence in the coal mining area under the Eighth Mining Bureau of Shanxi Province has affected the normal production and life of hundreds of villages, tens of thousands of acres of farmland and hundreds of thousands of people.
Underground engineering drainage water inrush (mud outburst). In underground projects such as mines, tunnels and civil air defense, due to the discharge of groundwater or water inrush (mud outburst), the groundwater level drops rapidly, and the surface rock and soil above it loses balance. When underground cavities appear, they will collapse. This kind of human activity plays a great role in karst ground collapse, and the resulting karst ground collapse is the largest, strongest and most harmful. The karst ground collapse in many mining areas and railway tunnels in China is caused by this activity.
Excessive pumping of groundwater. Excessive pumping of groundwater will reduce the groundwater level, aggravate the potential erosion, make the rock mass and soil out of balance, and cause ground collapse when there are underground cavities. This kind of ground collapse is also very common in karst areas, mostly in urban areas.
Artificial water storage. This not only increases the water load in a certain range, but also increases the groundwater level, which strengthens the potential erosion and erosion of groundwater, thus causing ground collapse. For example, the ground collapse caused by the Baxu Reservoir in Nandan, Guangxi, caused all the reservoir water to leak.
Manual loading. Manual loading above the development site of hidden caves will also lead to ground collapse. For example, the ground collapse of the yard of Wuhan Zhongnan Rolling Mill is caused by man-made stacking.
Artificial vibration. Blasting and vehicle vibration can also cause ground collapse in the hidden cave development area. For example, the blasting in Wuliang Village, Gui County, Guangxi caused the ground to collapse, forcing the whole village to move.
Surface water leakage. Leakage of water pipeline or poor drainage of the site will cause surface water infiltration or chemical sewage infiltration, and also cause ground collapse. For example, the ground collapse of the second paper mill in Guilin, Guangxi, was caused by the infiltration of chemical sewage discharged from the factory.