DISASTER ANALYSIS AND COUNTERMEASURES OF LAND SUBSIDENCE CAUSED BY COAL CUTTING IN CHINA

T HINESE GEOCRAPHICAL SCIENCEVolume: 13, Number 2. pp 130-133, 2003Scien e Press. Bciiing. ChinaDISASTER ANALYSIS AND COUNTERMEASURES OF LANDSUBSIDENCE CAUSED BY COAL CUTTING IN CHINASHI Tong-guang", JIANG Lu-guang', LI Yue, YANG Yong-liang1. partment of Urban Geographic Information System, Shandong Institute of Architeeture and Engineering, Jinan 2500/4P. R. China; 2. informalion Engineering University of the Chinese Peoples liberation Army, Zheng=hou 4.50052.P.R.Chinai. College af Population, Resources Environnent. Shanong Mormal t'niersiry, Jinan 250014, P. R. china4. Department of Entironmerual Sciences, Qingdao linirersity, Qingdao 266071, P. R.ChinaARSTRACT: In recent years, many coul-producing countries have paid great attention to the land subsidence causeby coal cutting. In China. because of the dense population in coalfield areas, the land subsidence hazard is more seri.ouN. After a brief analysis on the mechanism of land suhsidence, this paper gives a comprehensive and systematical aecount on all kinds of hazards caused by the land subsidence in China. The study shows that land subsidence has endan-gered land, buildings, traffic and communication lines, dykes and tlams. It also causes damage to ecologic al and sor ialenvironment. In orer to lessen the hazard of land subsidence. preventive measures should be taken to reduce the eollapse amount, such as extraction with stowing, banded mining system, succession and coordination mining system,orhigh-pressure nudnow between ruck strata. Measures of reinforeing or moving certuin buildings should also be take n toubridenee land and bring them undrol forres should he taken such as filling with spoil or fine breeze, excavating the deeper and covering the shallower landKEY WORDS: coal cutting: land subsidence; disaster analysis; countermeasuresCLC number: x43Document code: AArtiele: ID):002-0063(2003)02-1)130-04Underground cutting is the main means of coal cutting in depth and thickness of the coal bed. Unde r normalChina. Its output makes up 97%0 of the lotal outpuL, condilions, the subsidenee area on ground surfacThe main method of mining is long-wall working with larger than the exhausted area under groundcaving, which will inevitably cause large-scale land sub-silence(XIAO, 2001).With the increasing of coal ex- 1. 2 Land Subsidence Area in Chinaraction amount, the exhausted area expands rapidly.Land subsidence has become the most serious engineer- According to the prelininary statistics, land subsidenceing hazard and has caused serious influenee on the phys- has occurred in nearly 50 coalfields in China sinceical environment and social environment in coalfields. 1980. For example, there was a 60-km subsided areain Yangyuan Coalfield of Shanxi Province, 52-kminI MECHANISM OF LAND SUBSIDENCE AND SUB- Jiaozuo Coalfield of Henan Province, 30-km in FushunSIDENCE AREA IN CHINACoalfield of liaoning Province and 20-km in Pingding-shan Coalfield of Henan province. The subsidence area1. 1 Lund Subsidence Mechanismin Xuzhou Coalfield of Jiangsu Province was more thanubsidence volume was equal to 60%nCoal extraction destroys the original stress balance in 70% of the extraction volume, the area of land subsiembracing rocks and causes stress concentration. Once dence was 20% higher than that of coal extrac tion, thethe stress surpasses the intensity of the rocks, the depth of water in subsidence area was 2.5-4.Omstarts fo collapse area. The Acstatisties of xuzhou, Yanzhouvolume and area are related directly to the中国煤化工m;( Huaibei andd ua ate;2002-03-0lCNMHGBiography: SHI TonF-guang(1963-), nale, a native of Shandong Province, professor, specialized in the influene: of hutman activitiesanl cology und environnentDisaster Aalysis and Countermeasures of Land Subsidence Caused by Coal Cutting in ChinaHuainan in Anhui Province)coalfields in recent years, deformation with different characteristics may have dif-the subsidence area can be 0. 15-0. 24ha, as the result ferent effects on buildings. Ground slipping and deforof coal extraclion of 10 OOUt. Supposing the land sub- mation destroy the original balanee bet ween the buildlingsidenre area caused by each 10 000-t coal extraction is and its foundation. Following the reformation of stress0. 2ha. Imore than 200 x 10t coal extraction in plain balance, addlitional stress emerges in the building. Thiscoalfield in China per year may damage more than will lead to the buildings deformation and destruct4000ha of fine lan(YE, 1998)Buildings in different location in the slipping basin havedifferent dlamage characters and degrees. At the center2 HARM OF LAND SUBSIDENCEof the basin, the ground sinks vertically. It does ligdarmage to the building. On the edge of the basin, dif-2. I Damage to landferent stresses concentrate. Buildings will be damagedmosl. According to the observation in Yanzhou Coalfield(1) Forming slipping basins. Coal extraction causes (Shandong Province), the damage critical puints ofthe deformation of upper embracing strata. When the brick building are as follows:subsidence wave affects the earth's surface. this will degradient i=3mm/mstroy the original landform, posing great difficulty forhorizontal-deformation 8= 2mm/mfarming and irrigation. Furthermore, if the ground sub-h=0.2×10-3/msides below the ground water level, the ground will be It has proved that the damage degree of buildingswaterlogged and not be farmed. Land subsidence can even is not only relaled to the ground deformation, but alsodestroy the form of water-bearing stratum, leading lo de- related to the structure, span, length, height, planescent of underground water level and aridity of ground. form, building quality, material quality, service life etc(2)Geo-suture. During the course of mining flat-dipp- Sohard to forecast(QIAN and WANG, 1993)ng coal bed, geo-suture may emerge on the edge of slip-ping basin. Its occurrence, width and depth are closely 2. 3 Damage to Traffic and Communication Linesrelated to the plasticity, stickiness and the tensile defomation degree of the topsoil. Geo-suture may occur in elay (1)Damage to roads, railways, bridges and owhich has strong plasticity when the tensile deformation verts. There are many roads and mine railways in toalexceeds the limit of 6-10mm/m. Geo-sulure may also field. Land subsidence may cause subsidence of roademerge in arenaceous clay, clay sand or rock when the and railway foundations, make the road surface water-tensile deformation exceeds the limit of 2-3mm/m. logged or make the rail distorted or hung in the airGec-sulures destroy land continuity, pose difficulties for Bridges and culverts demand strict integrity and stabil-farming and may cause serious soil erosion(MA, 1999). ity. ' Their unit costs are high. Once they are damaged3)Collapse hole Collapse hole may emerge during by land subsidence, it is difficult to repair and wille course of mining in steep dipping of coal bed. Col- cause enormous losses.lapse hole can be divided into two kinds: funnel hole (2)Damage to underground pipelines Undergroundand notch hole. Collapse hole may cause humus erosion pipelines in coalfield mainly consist of gas-supply pipeland make soil poor in nutrition. In short, land subsi- ines, waler-supply pipelines and irrigation pipelines. Thedence affects the natural form and nutrition of land se- damage manifestations of underground pipelines can beriously. The affected land presents marsh-land and divided into three aspects: First, the original slope ofarid-land forms in physical properties and presents soil pipelines is changed. This will cause hindrance to thacidization and nutrition erosion in chemical properties, circulation and decrease the transport efficiency. See-thus making land quality reduce to a lower rank or make ond, soil deformation may pose additional stress to theland lose its use value.asses the limit in-egree surpassestensity, it may cause rupture of the pipelines. Further-2. 2 Damage to Buildings on the Groundmore, land subsidence may cause that the groundwatersurface surpass the level of pipelines. This will poseSurface slipping and deformation caused by underground greatne maintenancemining can be divided into three forms: vertical defor-中国煤化工. Lund subsidemation (sink, incline, curve and twist), horizontal mayCNMH Gon lines and powerdeformation (level slipping, tensile or compressed de- transsupsiueu or crooked. The jinese-formation)and shear deformation. Ground slipping and lasticity is also changed. In fact, land subsidence notHI TCJIANG La-gtL I yue ef al.only damages lines, but also poses a great threat to the subsidence coefficient is 0. 1 9 <0. 2. But its cost islife of people and domestic animalshigh, so this method is not used widely. Fine breezestuffing and spoil stuffing are widely used in Xinwen2. 4 Damage to Dykes and Damsnlan Provinceand Jilin Jilin Province)areas. By applyi. and subsidence may cause horizontal or vertical dis. this method to coal cuttingvillages, railways,may destroy the integrity and decrease the intensity and vation can be reduced s and dykesplacement of dykes and dams. Horizontal displacement roads, transmission lines and dykes, the cost of reno-waterproof ability of dykes and dams. Vertical dis(2) Banded mining system. If there are few villagesplacement may decrease their height. As a result, their in the mining area and the depth of coal bed is not moreability of intercepting flood is decreased. The than 400, banded mining system can be used. It canabove-mentioned situations may bring flood disaster and be divided into several forms such as strike directionse a great threat to the people's lives and properties. band, tile direction band, collapse band, filling bandmining system, ete. The subsidence amount of bandled2. 5 Damage to Ecological and Social Environmentmining system is only equal to 1/6-1/4 of long-wallmining system. Its subsidence coefficient 9=0.Large quantities of lands are reduced to marsh or wa- 0. 2, tangent of main-effect angle tgB=1. 0-2.0terlogged depression by land subsidence. The original horizontal displacement coefficient b=0.2-0.3,andplain-cultivation environment is reduced to the water its active period is shortenvironment. The destruction of water-bearing stratum (3)Succession mining system and coordination min-causes the descent of the ground surface anding system. Succession mining system is to mine in or-ency of imigation water resources. The transformation der of coal seams. It can reduce the overlapping influfrom irrigable land to dry land has reduced the harvest ence to the ground deformation. Coordination miningseriously. The subsidence of dykes and dams has posed system staggers the work faces in order to offset stressa great threat of flood to the people. Farmers lose part of from different strata. The following are some points thattheir lands because of land subsidence. The contradic- should be paid attention to: 1) The edge of mining istion between growing population and reducing land is the main damage area. So do not let the mining edgefarmers and coalmines are usually the unstable social deformation, so coal column is not allowed below vilfactors in the mining area. With the expansion of the lages. 3)A proper relation between the coalface and theexhausted-area, the problem of damage compensation building trend will contribute to a minor deformation ofand village moving is becoming more troublesome. It is buildingnot only an economic problem, but also a serious social (4)High-pressure mud-flood between rock strataproblemAfter coal extraction, the upper rock strata will formcrack area or low-sink area, Differe3 COUNTERMEASURES OF THE COMPREHENSIVE rock strata have different anti-formation strengths andPREVENTION AND CUREsink speeds. A flexible rock stratum has lower bendingstrength thaun aock stratum. so it sinks faster thanThere are three ways to lessen the damages of land the hard one. As a result, a space emerges between thesubsidence: First, adopt new mining techniques to re- upper hard rock stratum and the lower flexible rockduce the amount of subsidence and deformation. Sec- stratum. Injecting mud in time can prevent the strataond, reinforce or move the installations on the ground from sinking. According to the experimental resultsbefore mining. Third, reclaim the wasted lands in the Laohutai of Fushun Coalfield Liaoning Province)ubsidence areasubsidence amount can be decreased by 62%I Preventive Measures to Reduce Subsidence Amount 3. 2 Preventive Measures to Reduce Destructive Degree1)Extraction with stowing. Extraction with stowing In oH中国煤化工mee, fois the most effective means to lessen the subsidence. moCNMHGve way. The basisSands, fine breeze and spoil can be used as packing ofIs Le: anIi-iormation ability ofmaterials. Water-sand stuffing is more effective. Its ground installations and the forecast of moving amount ofisaster Analysis and Countermeasures of Land Subsidence Caused by Coal Cutting in Chinadence.The former can be obtained by analyzing to avoid mortar out-flowing. Until the mortar is settledround installations themselves and the later can be and drawn off, it should be covered with topsoil foroblained by mathematical models. To counter different 0. 5m thick(ZHAO and YANG, 2000). If subsidenceground deformations, relevant measures should be tak- area is elose to river or lake, river silt and lake mud canen. Concerning general brick houses, if its predicted be used as filling materials. In this way, steps of topsoildamage degree is below N, reinforcing is enough to stripping and covering can be eliminated, but dredgerssolve the problem. If its predicted damage degree is are needed.above I, moving should be considered. If the fore-(3) Excavating the deeper land and coveringcasting subsidence of railways and roads is too serious, shallower land. If the ground water level is near to thetheir routes should be changed beforehand in ordeground surface, light subsidence may cause the landensure transportation and communication unblockedwaterlogged. This kindally not suitablefarming and its water is too shallow to raise fish, forming3. 3 Hamessing Measures to Land Subsidencewasted landscape"in coalfield. According to statisticsof Huaibei Coalfield. this kind of subsidence area cowAccording to the technological feasibility and economic ers one-fourth of the total subsidence area. The coun-reasonability, we can take measures suited to local termeasures to such subsidence area are as follows:conditions to renew soil fertility of sink lands, eliminate excavating the deeper land until it is suitable to raisemining disadvantages to the environment.fish, and covering the shallower land until(1)Filling with spoil. Spoil is the main pollution farming(BIAN and ZHANG, 1994). Tests in Shen-source in coalfield. In China, its annual output is about zhuang of Huaibei Coalfield indicated that it calls for150 x 10%t, but its comprehensive utilization ratio is lessinvestments and quick yield return. The harnessthan 15%. Spoil not only pollutes the environment, but(LIalso seizes the cultivated land. The gravity of spoil hiSo it is an ideal method and is worth spreadposes a great threat to pit shaft. So, filling with spoil is inga good idea of harnessing hazard by waste materialsBefore filling up the subsidence area, we would better REFERENCESstrip topsoil first, then fill with spoil until thelevel is only below the original level by 0. 5m, and fiBIAN Zheng-fu, ZHANG Guo-liang, 1994. Theory and method ofland refarm engineering in coalfield[J]. Regional Research andmally cover it to the original level with the topsoil. In Development, 13(1):6-9.(in Chinese)this way, the original soil fertility is preserved. Daihe, CHEN Yong-qi, 2000. Practice on land refarming by spoil ina mine in Huaibei Coalfield, has reclaimed 4ha land in subsidence land in coalfield[J]. Coal Mine Environmental Prothis way since 1984, and has achieved good economic tection, 14(2 ): 25-27. (in Chinesereturns and social effect(CHEN, 2000)LIU Jin-hui, 2000. Planning and designing on ecological engi-(2)Filling with fine breeze. Fine breeze is a kind of neering in subsidence area caused by coal cutting[J].Minepower waste discharged by coal-burning power stationsSurveying,(1): 44-45, 27.(in ChineseAccording to the statistics of power stations in the south MA Feng-hai, 1999. The characteristics of land subsidencecaused by coal cutting and its resolve passes [J]. Coal Mineof Shandong Province. For a power station, its fine Environmental Protection, 13(4):46-47.(in Chinesebreeze discharge amount (per 10@t) each year is equal QIAN Yi, WANG Yun-gang, 1993. Present situation of subsi-to the installed capacity (per 10k W)in number. For dence area caused by coal cutting and its ecological developmentinstance, a power station with 1. 2 x10kW installed [J]. Coal Mine Enuironmental Protection, 7(2): 32-37. (incapacity will discharge fine breeze 1.2%t each Chinese)year. Atpresent, the discharge amount of fine breeze in XIAO He-ping, 2001. Important geological hazards of coal-mineChina has reached 50 million tons per year, while its and its prevention measures in China[J]. The Chinese Journalcomprehen sive utilization ratio is only about 25%. It of Geological Hasard and Control, 12(1): 51-54.(in Chiis estimated that the seized land by fine breeze in China YE Dun-he, 1998. About the environment problem on the coalhas reached 33 300ha by now. It pollutes the air and field [J]. Coal Mine Environmental Protection, 12(1):4地购山中国煤化工CNMHGbsiding larthe subsidence area. Alike filling with spoil, the topsoil byocnentae (. rcumstantiae. 20(2): 213should he stripped first. Dykes should be made in order218. (in Chinese)