Classification of prone degree of land subsidence in China

4.5. 1 Discriminant characteristics of classification of susceptibility to ground subsidence

Ground collapse is mainly divided into karst collapse and goaf collapse.

(1) karst collapse

The geological environment conditions and influencing factors of karst collapse are mainly the existence of open karst caves, loose sediment coverage and dynamic conditions of water activities.

China's Yunnan-Guizhou Plateau, hills, basins and plains in South China are the areas with the most and most concentrated karst collapse disasters. Especially in the hilly basin of Hunan and Guangxi, continuous pure carbonate rocks are widely distributed, and modern karstification is strong, including karst caves, karst troughs, underground rivers, tiankeng, shafts and natural bridges. Karst collapse is mainly soil collapse and a small amount of bedrock collapse. Karst collapse is mainly concentrated in peak-cluster valleys, peak-forest plains, hilly basins and valley terraces with thin soil layer, developed underground karst and strong groundwater activity, which are mainly caused by mine drainage and groundwater pumping. Yunnan-Guizhou Plateau is dominated by karst depressions and basins, while Guiyang area is a peak forest plain with strong karst development. The fluctuation of groundwater level is mostly on the bedrock surface and its vicinity, which is mostly caused by pumping and reservoir storage except natural collapse.

Carbonate rocks with continuous distribution and pure thickness are favorable conditions for karst formation and development. The Cambrian and Ordovician limestone strata in northern China are thick and pure, with karst development. Taihang Mountain, Luliang Mountain and Yanshan Mountain are covered with coal measures strata in the upper part, and tertiary glutenite and quaternary loess in the local part. A large number of collapse columns are developed in the uplift and fold belt and marginal piedmont belt of Taihang Mountain, which is an important geological disaster in coal mining. Modern karst collapse is mainly developed in shallow covered karst areas in hilly plains.

Thin layer or dolomite or siliceous, argillaceous interlayer or interbed and impure limestone and dolomite are generally poorly developed, so it is difficult to form karst collapse.

(2) goaf collapse

The collapse of goaf is caused by the destruction of ore body (layer) by goaf and overlying strata. After the underground coal seam is mined, the direct roof strata in the goaf move downward and bend under the action of its own weight and overlying strata, and then fracture and delamination occur. When the mining area is large enough, the rock strata move to the surface. The surface formed a subsidence basin much larger than the goaf. Goaf collapse is distributed in mines and their surrounding areas all over China, among which coal mine collapse is the most prominent.

Table 4.6 shows the different characteristics of the classification of the susceptibility degree of ground collapse caused by karst collapse and goaf collapse.

4.5.2 Briefly describe the zoning of land subsidence susceptibility and the characteristics of each zoning.

According to the characteristics of the above classification of land subsidence susceptibility, the land subsidence susceptibility in China is classified, and the results are shown in Figure 4.3 and Table 4.7.

Figure 4.3 National Map of Land Collapse Vulnerability

Figure 4.3 National Map of Land Collapse Vulnerability

Table 4.6 Discriminant Characteristics of Classification of Vulnerability Degree of Ground Collapse

Table 4.7 Ground Collapse Vulnerability Zoning Table

4.5.2. 1 high incidence area of land subsidence

(1) prone area of land subsidence in hilly plain of Hebei, Xuzhou and Huaihe (H 1)

Including Laiwu, Zaozhuang, Taian, Linyi, Yongcheng coalfield in eastern Henan, Xuzhou in northern Jiangsu and so on.

Karst development in this area is moderate to strong, and the thickness of overburden is generally less than 30m.

The goaf subsidence area in this area is more than 5 18.86km2, and the maximum subsidence depth is12.5m.: : 62 1 more karst collapses, resulting in direct economic losses of10.75 billion yuan.

(2) High incidence areas of land subsidence in Jinzhong and Jinnan (H2)

Including the mined-out areas of various mines in Shanxi.

The soluble rocks in this area are mainly Cambrian limestone and Ordovician limestone, with strong karst development. The upper part is covered with coal measures strata, and the tertiary sand, conglomerate and quaternary loess are partially covered. It is located in an area with strong neotectonic activity, loose lithology, many caves, strong water conductivity and easy water inrush.

The area is dominated by goaf collapse, with the collapse area of 529. 14km2, resulting in direct economic loss of 331173,000 yuan.

(3) China southern hilly basin (H3) land subsidence prone areas.

Including the hilly plains in the middle and lower reaches of the Yangtze River in Anhui and Jiangsu, western Zhejiang, Daye, Huangshi, Yangxin, Ezhou, Tongshan and Tongcheng in Hubei. The piedmont plain basin in Jiangxi, the hilly basins in central and southern Hunan, western Guangxi, northern Guangxi and northern Guangdong.

The elevation of this area is less than 200m, which is mainly composed of peak forest plains and hilly basins, with continuous pure carbonate rocks and strong karst development. The overburden thickness is generally less than 30m, and the overburden thickness along the hilly plains in the middle and lower reaches of the Yangtze River is 10~80m ~ 80 m, and the groundwater level is shallow.

Karst collapse is common and serious in this area, with more than 3,330 places and more than 22,000 collapse pits, which are mainly distributed in the peak forest plains and basins. The collapse pits are caused by drainage and groundwater pumping in the pits. The largest subsidence group in Guangxi is in Xincheng County, covering an area of 5.5km2, and the density of subsidence pits is between 500 ~ 1000 /km2.

(4) The mountainous areas in eastern Chongqing and western Hubei are prone to land subsidence (H4).

Including eastern Sichuan, northeastern and southeastern Chongqing and western Hubei.

The ground collapse in this area is mainly karst collapse, which mainly occurs in limestone and marble distribution areas.

(5) The prone area of land subsidence in Yunnan-Guizhou Plateau (H5)

Including coal mines in eastern Yunnan, Liupanshui, Bijie and Zunyi, phosphate mines in Guiyang and Qiannan, and mercury mines in Zunyi and Tongren.

The elevation of this area is above 1000m, and there are many depressions and basins. Guiyang area is a peak forest plain with strong karst development. The thickness of overburden is generally 10~30m, which is greater than 10 ~ 30m in the faulted basin. The groundwater is shallow and fluctuates above and near the bedrock surface.

Collapse is very common in this area, about 2050 places have been found and more than 25000 collapse pits have been found. In addition to natural collapse, most of them are caused by pumping and reservoir storage. There are more than 1800 collapse pits in Shuicheng basin due to pumping groundwater, and the collapse density in the basin is 268 /km2. The total area of karst subsidence area in Kunming is 5.5 1km2.

Land subsidence prone areas in 4.5.2.2

(1) Land subsidence prone area in hilly area of Northeast China (M 1)

Including Mudanjiang, Jixi, Qitaihe, Yichun and other places, central Jilin.

The mountainous area in this area is more than 500 meters above sea level, and there are few soluble rocks distributed and exposed, mainly Proterozoic, Cambrian, Permian limestone and marl, with weak karst development. Mainly for goaf collapse.

The land subsidence in this area is relatively dispersed, and the subsidence area of Jixi, Hegang, Shuangyashan and Qitaihe River is 500km2.

(2) The prone area of ground collapse in Yanshan, Taihang and Funiu hills and plains (M2)

Including Fushun, Fuxin, Tiefa, Benxi, Beipiao, Nanpiao and Shenbei coalfields in the hills and foothills of Liaodong Peninsula. Fangshan District and Mentougou District in the west of Beijing, the loess plateau west of Luliang Mountain, Taihang Mountain and Zhongtiaoshan and the surrounding hilly areas, and the mined-out areas in Handan, Xingtai, Zhangjiakou and Tangshan are prone to ground collapse.

The karst development in this area is moderate to strong, and the carbonate rocks in this area are mainly Proterozoic, Sinian, Cambrian and Ordovician limestone. Locally contiguous, karst development is weak to moderate, and the thickness of Quaternary caprock is between 10~50m ~ 50m.

There are 7 karst collapses and more than 300 collapse pits in this area. There are 3 collapse columns and 80 collapse columns. It is mainly caused by pumping karst groundwater, followed by earthquake collapse and mine drainage. There are few collapse points in this area, but they are concentrated. There are 32 mined-out collapses in Pingdingshan, Jiaozuo, Hebi, Jiyuan, Yima, Yongcheng and other mining areas, with an area of 162. 13km2, resulting in economic losses of more than 38.39 million yuan.

(3) China southern hilly basin plain (M3) land subsidence prone areas.

Including northwest and south-central Hunan, Pingxiang-Fengcheng, Leping, Jingdezhen, Ruichang-Jiujiang, Yongxin-Anfu, Ji 'an and Gannan karst basins, coal, tungsten and copper mining areas, Chun 'an-Hua Kai, Anji-Lin 'an in western Zhejiang, Dongyang in central Zhejiang and northern Guangdong.

Carbonate rocks are scattered in this area, and the karst development degree is different: Hunan is generally strong to medium, and East Jiangxi-Hangzhou is generally medium to weak. The thickness of Quaternary overburden is generally less than 10m, and the groundwater level is generally shallow. Mainly karst collapse.

(4) The Qin-Ba Mountain area (M4) is prone to ground collapse in hilly and gully areas.

Including southern Shaanxi.

Carbonate rocks of Permian and Triassic are exposed in this area, and karst development is weak.

There are some unexplained crashes.

(5) Land subsidence prone areas in Sichuan-Yunnan (M5) high and Zhongshan areas.

Including the alpine valleys in the western Sichuan Plateau, northeastern Yunnan, the middle and lower reaches of Jinsha River, Nujiang River, Yuanjiang River, Lancang River and Jiang Lixian.

This area has high altitude and strong terrain cutting, and belongs to the karst landform of Zhongshanxia. The exposed soluble rock stratum is complete, and the karst development is weak to medium, and it is strong locally.

There are 17 collapses and 166 collapse pits in this area, which are mostly caused by natural collapse and reservoir impoundment.

(6) Land subsidence prone areas in Tianshan Mountain and West Junggar (M6)

Include that coal-bearing belt in the southern and northern foothills of Tianshan mountain and the low hills of western Junggar.

Neotectonic movement caused Tianshan Mountain to uplift strongly, faults developed, metamorphic rocks and magmatic rocks were widely distributed, Quaternary sediments were abundant, and loess was distributed in the foothills. There are also Mesozoic Triassic and Jurassic coal measures strata.

The area is dominated by goaf collapse, with 48 collapses.

Low prone area of land subsidence in 4.5.2.3.

(1) Low-prone areas of land subsidence in eastern plains and mountainous areas (L 1)

Including the northeast mountainous area, plain and North China plain.

The mountain area in this area is above 500 meters above sea level, and the plain area is below 200 meters above sea level. The distribution and exposed area of soluble rocks are less, mainly Proterozoic and Cambrian, Permian limestone and marl, with weak karst development. This area is covered by a large area of Quaternary soil, the thickness of which is generally greater than 100m, and the soluble rocks are buried deeply.

Karst collapse is less.

(2) The central plateau, mountains and basins are low, which is prone to land subsidence (L2).

Shaanxi, Gansu, Ningxia, Mengshan Plateau, Qinba Mountain Area and Sichuan Basin.

Soluble rocks are scattered in this area, with a small amount exposed in Yanshan Mountains, and karst development is weak.

There is basically no collapse in this area.

(3) The western plateau, platform and basin are low prone to land subsidence (L3)

Mainly for the Qinghai-Tibet Plateau, Inner Mongolia platform and Xinjiang and Qinghai desert basins. The elevation of this area is generally above 2000m, and the elevation of desert basin is generally above1000 m. The southwest of this area is a relatively complete plateau with many lake basins. The eastern and northwestern regions are strongly cut, showing deep valleys with great height difference. Carbonate rocks of Paleozoic and Mesozoic are mainly exposed in this area. Modern denudation is dominated by physical weathering, freeze-thaw and gravity, and karst is extremely weak.

At present, there is basically no collapse in this area