A New Mode of Coal Mining Under Buildings with Paste-Like Backfill Technology

De,2002Journal of China University of mining technologyVol. 12 No. 2A New Mode of Coal miningUnder buildings with Paste-LikeBackfill TechnologyCUlJian- gange崔建强), SUN Heng-h(孙恒虎), HUANG Yu-cheng(黄玉诚)School of Resources and Safety Engineering CUMT, Beijing 100083, ChinaAbstract: The formation of the paste-like backfill technology was introduced briefly in this paper. From theactual cases of coal mines a new mode of coal mining under buildings with the technology was proposed. Andits specificity was analyzed and a further introduction to the full-sand-soil solidifying material was given. Themain parts of the backfill system such as the backfill preparation system the pipeline transportation systemthe backfill systems in fully-mechanized mining faces and the backfill process, were presented emphaticallyKey words: mining under buildings paste-like backfill full-sand-soil solidifying materiaCLC number: TD 823. 7 Document code: A Article ID: 1006-1266 2002 02-0143-051 Introductionbackfill mining is the most effective in the control ofWith the rapid increase of the demand of social surface subsidence and deformation and the recoveryand economic development, the conflict betweeof coal. The density of backfill body and its subsicoal shortage and economic development is becomingdence contraction influence the movement and defor-more and more conspicuous. More attention has mation of surface and surrounding rock directlybeen paid on coal mining technology under build. The solidifying backfill mining techngs. The present coal mining technology under widely applied in royal and nonferrous mines for itsbuildings can not be widely applied for its some backfill body has the following advantages such asshortages such as the poor effect of surface subhigh density little subsidence contraction, and edence and deformation controlling the serious pollu- nough strength and stiffness. With the developmenttion of underground operation environment and the of modern science and technology the solidifyinglow recovery of resources. Paste-like backfill tech- backfill mining technology has been improved andnology has outstanding advantages such as the wide developed greatly. Based on the development trendsupply of backfill materials the low cost of backfill- of solidifying backfill technology Professor SUNing, the easy preparation of slurry and the high Heng-hu proposed a new mode referred to as paste-trength of backfill body. It can control surface sublike solidifying backfill. The new mode s specificityidence and deformation effectively gain a highis that it has not only the advantages of both hycovery, and does not pollute underground operation draulic backfill and paste backfill suchenvironment. Using the new mode, harmless and slurry fluidity and the easy pipeline graytrans-non-pollution mining under buildings can be realportation for the former, and the great backfill bodyHlittle dehydrating for the中国煤化工2 Proposal and Specificity of the New ModeCNMHGmnt has the poor caIn all the modes of coal mining under buildingspability of fine particles solidifying. When the denReceived date 2002-04-25144Journal of China University of Mining technologyVol. 12 No. 2sity of backfill slurry is lower than that of paste, the4)Selection of backfill preparation stationslurry is easy to transport through pipelines by graytes: The backfill system must meet the demand ofity which will result in the loss of fine particles( in- the ratio of total length to height difference of pastecluding cement particles in the dehydrating pro- like slurry transportation. Moreover, the transcess. So the subsidence contraction of its backfill portation of backfill materials on the earth s surfacebody increases and the strength decreases which must be taken into account so as to lower the backfillleads to the loss of binder and the serious pollution of cost farthest for the backfill amount is greatunderground operation sites. When the density of5)Coordination: To assure the production ofbackfill slurry is close to that of paste its fluidity fully-mechanized working faces and the quality ofbecomes poor and difficult to transport. Therefore backfill body the processes of mining and backfillthe key to the realization of paste-like backfillmodemust be coordinated well. By now there is no relais to research and develop a new kind of binder. Ittive engineering experiencenecessary for this binder to have the capability of so- 3 The New Mining Mode Under Buildingslidifying fine particles and for its backfill body tomeet the need of strength. Meanwhile it must haveand Its System Layout3.1 Full-sand-soil solidifying materialrange of backfill materials and a lowfill costThe full-sand-soil solidifyThe research group leaded by Professor SUN of powder made of some industrial waste, such asHeng-hu has developed a new generation bindeblasting-furnace slag smelter slag and proper porfull-sand-soil solidifying material. With the new so- tion of natural minerals and chemical catalystslidifying material the paste-like backfill mode is through milling and mixing. It has a powerful capaforming gradually which absorbs the advantages of bility of solidifying sandy soil and industrial wastethe modern solidifying backfill and spurns its disad( such as tailings containing a high percentage ofvantageclay. Hence comes its name full-sand-soil solidifyingBased on the knowledge of solidifying backfill material, called full-sand-soil material for shortengineering practice the actual situation of coalCompared with Portland cement the full-sandsoil material has its own specificity in the respects ofof coal mining under buildings is setechnological property production process and engithis new mode and its system design have botlneersomething similar to the solidifying backfill technol- fying fine particles. Under the condition of equalogy in metal mines and its own characteristicsdosage its strength is 23 times that of cement. Un-1)Backfill material: The newly developed full- der the same strength demand its dosage is lesssand-soil material is adopted as binder and debris than half that of cement. Compared with regular ce-(waste from coal mines )and fly-ash( waste from ment, its early strength is high, and 7-dayssteam electric plants are used as aggregatestrength and 28-days strength can reach that of2)Backfill area: Coal deposits takes the shape 425" and 525"cement standards respectively. Theof seams, most of which have a low angle, so the process of producing the full-sand-soil material is toarea to backfill is great and backfill slurry have to be engulf a large amount of industrial waste and totransported farther. Compared with metal deposits produce super binder with good property and widenormally taking the shape of block or vein, the ratio usel中国煤化工 on costs lowof total length to height difference is largerCNMH Gn. Therefor, the full3) Backfill capacity: Generally fully-mecha- sand-soil material will not only find wide applicationsnized working faces in a coal mine has a larger pro- in mining communicationconstruction, waterductivity than a metal mine. So, a larger backfill ca- conservancy and oil projects but carve out a com-pacity of thewill system is neededpletely new way to reutilize industrial wasteCUI Jian-qiang et alA New Mode of Coal Mining Under Buildings with Paste-Like.1453.2 The system layout of paste-like backfill min- 3. 2. 2 The pipeline transportation system of paste-ing under buildingslike backfill slurry3. 2. 1 Backfillon station systemFirstly the layout of the pipeline transporta1)Location selectiontion system must meet the demand for the backfillDistinguished from paste backfill one of the capacity and make the backfill operation be highspecificity of the paste-like backfill is that the fluidi- quality efficient safe and economic. It is not perty of its slurry is excellent. Without or with a little mitted for the backfill pipeline to be laid upwardtransportation pressure its slurry can be transporteMeanwhile too many turns should be avoided so asto backfill sites. For this reason when the location not to result in the natural pressure loss of backfillof a backfill preparation station is selected the de- slurry and pipeline blocking. The pipeline to under-mand for the ratio of total length to height difference ground should be laid in the auxiliary shaft or aishould be met firstly so that the paste-like backfill shaft as far as possible. Utilizing the existent shaftsslurry flow by gravity can be ensured. Secondly the roadways and ground installation can decrease thetransportation work of a backfill materials on the backfill pipeline laying cost and also make theearth s surface should be minimized furthest. The pipeline onveniently inspected and repaired. Thecapacity of a backfill preparation station should be backfill pipeline layout in a coal mine can be seenabout 2.0 times that of the backfill mining face. Fig. 1. Its backfill pipeline is laid through a backfillSince a coal face usually has a large productivity per bore-hole auxiliary shaft main entry return dipyear so lowering the backfill material transportation tail-entry to the backfill sitecost will be of outstanding sense4L6且圈2) Layout of a backfill preparation stationBased on the capacity of a backfill preparationtation, the specificity of backfill materials and thepractical experience of solidifying backfill mining inmetal mines it is more suitable for a backfill preparation station to adopt a two-step mixing system , ie.,the first-step mixing drum prepares mortarmade from debris fly-ash and water with a densitbout 73%; and the two second-step mixing drumFig. 1 Backfill pipeline layout at the begining periprepares paste-like backfill slurry with a density1. Backfill preparation station 2. Town buildings 3. No 6 shaftabout 75% made from the full-sand-soil material and 4. Filling pipe 5. Entry at-570m level b Entry at-710m levelthed by the first-step mixing7. Return dip 8. Transp10. Fully-mechanized mining face l 1. Head-entryo ensureoperation of apreparation station two mixing drums are set forFrom the pipeline layout in Fig. 1 the actualeach step. When one of the two first-step mixing ratio of total length to height difference can be calcudrums is working normally the other is alternate. lated by the following formulaBoth of the two second-step mixing drums are workN=L/Hing normally at the same time. When something is where N is the ratio of total length to height differwrong with one of the second-step mixing drums ence L is length of the backfill pipeline, L=lABIthe other can produce backfill slurry by itself. The中国煤化工+|EF|inm,andHadvantage of the layout is that when one of the mix-CNMHGce between the slurrying drums has something wrong, the production of entrance on the earth s surface and the slurry exit atslurry does not be influenced so as to ensure the connd backfill site , H= the height oftinuity of the backfill processpoint A-the height of point F in mOn the basis of the laboratory research on the146Journal of China University of Mining technologyVol. 12 No. 2paste-like slurry flow specificity and the similar engi- 3. 2. 4 The process of backfill technologyneering experience of metal mines N=3-6 is the1) Preparation processmost suitable value for the paste-like slurry to beThe preparation process of backfilling includestransported through a pipeline by natural pressuresealing of the flexible shuttering, linking of the3.2.3 Backfill system in fully-mechanized working backfill pipes communicating between the backfillfacessite and the backfill preparation station cleaning upThe gob resulted from backfill mining is filled of the head-entry drainage ditch and so onwith backfill materials tightly. In the process of de2) Backfill processformation with surrounding rock the backfill bodyWhen the preparation operation is accomwith certain strength and stiffness increases the ca- plished the backfill preparation station begins thepacity of surrounding rock effectively and gives some backfill operation. Firstly the backfill pipes isload-bearing capacity towards roof strata gradually. washed by using clean water and the pipeline is inA reasonable roof- controlling area can be obtained spected to determine whether it leaks or not. If all isfrom a site test and the strata control theory so as to OK, then slurry is transported down through theensure the safety of backfill operation. Thus along pipeline. In order to prevent the washing waterthe working face a row of hydraulic props should be from flowing into the gob a valve should be set upset in the gob behind powered supports. The dis- before the pipeline is laid to the backfill site. by thistances between hydraulic props and between hy- way the clean water resulted from the pipelineprop row and posupports, and the washing may be drained to the head-entry ditch di-width of each backfill strip can be obtained through rectlynumerical simulation and in-situ tests on the basis ofBackfill workers operate at the T junction ofroof stability mining depth tectonic stress and so the tail-entry when backfill begins. Attention shouldon. Thus a backfill road is formed between hy- be paid intently on backfill operation. When abnordraulic props and powered supports. Flexible shut- mal cases occur relative measures should be taken attering is set up along a side of the gob against hy- oncedraulic props to support backfill slurry and filter wa-While the gob is being filled with slurry duringter. Its layout can be seen in Fig. 2. The backfill the backfill period little water can be dehydratedsystem' s advantages are that mining and backfill from the seams or the flexible shuttering andprocesses are independent of each other its large fil- drained to the head-entry which prevents it fromtering area is good for the increasing backfill body's flowing to the working face and causing pollution toearly strength and the filtered water can flow to the the operation environmenthead-entry directly and not result in polluting of the3)Closing processworking faceWhen backfill slurry reaches at the predetermined position the backfill preparation station stopproducing slurry. To prevent the backfill slurryfrom detaining and solidifying in the pipes to blockthe filling pipe or make its radius decreasebackfill pipeline is washed using clean water for ahen there is no slurry flowing out atthe中国煤化工。CNMHG4he Estimation of Surface SubsidenceFig 2 Backfill pipeline layout at the begining period1. Head-entry i 2. Tail-entry 3. Powered supportProbability integration is the traditional methodto estimate surface subsidence resulted from coal7万数Flexible shuttering X. Backfill roadstrip 8. Complete backfill stripmining under buildings. Take the feasibility re-CUI Jian-qiang et alA New Mode of Coal Mining Under Buildings with Paste-Like.147search on one coal mine s paste-like backfill mining The seam thickness including 5 coal seams is 10.6under buildings as an example. The calculation scope m and the average seam dip is 21. According tois the full subsidenceBased on the minirthe relevant literatures on solidifying backfill techarea's empirical values of the parameters for the nology subsidence coefficient q=0.02-0 05,tan-probability integration surface subsidence is esti- gent of the main influence angle taken by mediummatedstable strata tanB=1. 7 and horizontal moving coefc Its mining depths are 971, 1241 and 701 m in ficient b=0.3. The calculation results are listed inrend direction of the main section, at the lower Table 1boundary and at the uppeTable 1 The estimation of surface subsidence induced paste-like backfill miningunder buildings in a coal mineCalculationMax subsidence Max dippingMax curvatureMax horizontalsectionW/mm iAmm m 1) KA103ment U/mm deformation E/(mm mMain section in the trend direction 198-495 0. 35-0.870.009-0.0059-1480.16-0.40Main section in the rise direction 198--490.27~0.680.0006-0.0014Main section in the dip direction 198--495 0 42-1. 00.0014-0.003451-1290.17~0.42From Table 1, both surface movement and de- it can also reutilize a large amount of industrialformation values are smaller than the deformation waste. These advantages will make the backfill coststandards of No. 1 protection regulation for masonrdecrease greatly. Consequently the paste-tructure buildings in China, that is max dipping fill mode will carve out a new way for coal miningcoefficient i<3. 0mm/m, max curvature K<0. 2 under buildings. With the paste-like backfill techX 10/m, max horizontal deformation e< nology, the new mode of coal mining under build-mm/mings will certainly find application in solving the en5 Conclusionsvironment pollution resulted from debris and flyash and recover a large amount of coal under buildBased on the existent backfill modes and the ings, Therefore to the sustainable development oftrend of modern backfill development a new backfill Chinese coal mining the new mode will have a greatmode, paste-like backfill technology is put for- and far-reaching strategy meaningward. Its binder has good quality and low price andReferences[1]孙恒虎黄玉诚杨宝贵.当代胶结充填技朮M]北京治金工业出版社,2002[2]周国铨崔继宪刘广容等建筑物下采煤M]北京媒炭工业出版社1983[3]何国清杨伦凌赓娣,等.矿山开采沉陷敩M]徐州冲国矿业大学岀版社,1991[4]隋旺华.开采沉陷土体变形工程地质研究M]徐州冲国矿业大学出版社,1999中国煤化工CNMHG