Study On Water Prevention And Control In Deep Underground Mining Of Lindai Bauixte,Guizhou

With the rapid economic development of our country,aluminium demands become increasingly pronounced.Bauxite,as a raw material for refining aluminium,its reasonable exploitation and safe production play an important role in the national economy development.In China,most bauxite deposits belong to sedimentary type,which alwalys coexist with limestone layser where karst is strongly developed.Strong water conductivity and heterogeneous water abundance of limestone layer,and fracture existence of the geological structure,lead to hydrogeological conditions more complex and unpredictable.Once bauxite mining connected with limestone layer,it is prone to serious water inrush problems,and cause irreversible economic losses and casualties.Besides,in order to meet social and market demands of aluminum,bauxite mining becomes increasingly towards to deeper layer with more complex hydrogeological conditions,which bring more severe water inrush to our country.Therefore,it is urgent to study bauxite deep mining and water prevention.Lindai bauxite mine of Guizhou Province is a typical karst mine in Southwest China,where mining has lased for decades and its designed mining amount is 15×10⁴ t/a.When the vertical mining reached 1190m depth,it occurred severe water inrush.Because both water inrush source and the hydrogeological conditions below this layer are not clear,bauxite mining under 1190 m depth has to be stopped,which is amost167.76×10⁴ t.In this study,Guizhou Lindai bauxite mining area was selected as study area.Karst groundwater system was used as theory support,and"water inrush source identification"and"water inrush channel identification"were used as technical support,to analyze geological and hydrogeological conditions of study area.Groundwater dynamics calculation was used to recognize mine water inrush mechanism.On these basis,potential water inrush sources were identidied during deep mining in Lindai bauxite mining area.Then,floor water inrush theory,BP network model,AHP and GIS technology were used to analyze influences of water resisting layer safty,reservoir leakage and surface water influx on deep extended mining,respectively.Finally,a reasonable scheme for water prevention and mining system was designed for bauxite mining under 1190 m depth layer in the study area.This study not only scientically answered to“what is water inrush mechanism of 1190m depth mining in Lindai bauxite area”,but also solved the difficult problem of"whether bauxit under 1190 m depth can be mined and how to mine it".Firstly,geology,hydrological geology and mine production data of study area were collected.According to groundwater system theory,stratum lithology,groundwater boundary,topography and tectonic characteristics were analyzed at different scale of"regional-mining area-shaft",and karst development degree and fracture structure characteristics were indentified at different depths of"ground-shaft-tunnel",which are aimed to find potential sources of water inrush during bauxite deep mining in Lindai area.Conclusions are as follows:（1）Regional area can be divided into three hydrological unit systems,including of hydrogeological unit system of Zhanjie syncline area（I）,hydrogeological unit system of Lindai inverted monoclinic area（II）and hydrogeological unit system of Zhongzai-Yanlong monoclinic area（III）.In which,Lindai bauxite mine belongs to the hydrogeological unit system of II,and its hydrogeological condition belongs to medium-complex type;（2）The vertical movement of groundwater in regional area can be divided into four zones,followed by permeable zone（I）,seasonal fluctuation zone（II）,saturation zone（III）and deep circulation zone（IV）.The lower limit of karst development of Lindai bauxite mine is 848m;（3）Mining under 1190m depth layer in Lindai bauxite mine,faced to three potential water inrush threats,which are indirect water filled aquifer from Qixia-Mao formation（P₁q+P₁m）karst cave and fissure water,water seepage in Yingyan reservoir and the surface water injecting to tunnel through new channel caused by karst subsidence.Secondly,the development direction,degree and regularity of karst development in deep mining area are further revealed by tunnel logging,setting up groundwater level observation network and pumping test.Combining the hydrogeological conceptual model of mine area,the water inrush mechanism in 1190m tunnel is identified.Comprehensive utilization of hydrogeological analogy method and steady flow analysis,forecast Lindai bauxite mining water inflow 150m downward（the 1040m tunnel,which is the lowest mining layer）.Conclusions area as follows:（1）The mechanism of water inrush during mining under 1190m depth,is mainly caused by strong karst development of water bursting zone,and its vertical shaft is just located in this zone;（2）The main direction of fault structure in mining area is north-south,and its development degree gradually decreased with the increase of mining depth.The main tunnel in 1190m tunnel did not reveal any fault;（3）When the impermeable layer is not damaged,normal water inflow in 1040m tunnel is 4743.38m³/d,and the maximum water inflow is 14230.14 m³/d.Then,the first potential source of water inrush,that is indirect water filled aquifer from fissure water in Qixia-Mao（P₁q+P₁m）,is studied during 1190m deep mining.The lithology,stability,rock mechanics and rock mass quality of water blocking rock in Liangshan formation（P₁l）of the indirect water separation floor and the direct water separation panel（C₁b）are analyzed on the base of rock mechanics,water bursting coefficient and rock pressure failure theory.It was found that,if traditional method of separate evaluation was used to analyze extension mining to 1040m tunnel,Liangshan group aquitard or baizuo（C₁b）karst aquifer can be used as seam lower confining bed,in this case,the Liangshan group（P₁l）will be damaged because of its thin thickness and weak rock bearing capacity and Baizuo will be used as impermeable layer because of its itself is aquifer.That means the bauxite resources under the 1190m section are not suitable for mining.In this study,these two groups of rock formations will be combined as one composite type of water separation floor,to evaluate safety performance of this composite water resisting layer during deep mining to 1040m tunnel.Conclusions are as follows:（1）Compared with the original water level of 1963,water level decline of the immediate bottom Baizuo（C₁b）and indirect water filling aquifer Qixia-Maokou（P₁q+P₁m）are 123.26m and 3.86m,respectively.It shows that the rock mass of Liangshan（P₁l）still has water separation capacity;（2）When the extended blind incline shaft is mined to 1040m tunnel,the hydrostatic pressure of fissure water in Qixia-Maokou Formation（P₁q+P₁m）to the tunnel is 2.73Mpa,and the safety thickness of aquifuge is at least of 21.25m.Liangshan（P₁l）layer thickness is at the range of 16²3m,which can not afford Qixia-Maokou（P₁q+P₁m）hydrostatic pressure;（3）The composite impermeable rock mass thickness is at the range of 64⁹8m,which can bear the hydrostatic pressure of the Qixia-Mao（P₁q+P₁m）.It indicated that Qixia-Maokou（P₁q+P₁m）of the water inrush threat did not affect the extension of blind incline shaft in Lindai bauxite mining area.After that,the second potential source of water inrush in deep mining bauxite,Yingyan reservoir leakage,was studied.Based on 57 similar reservoirs seepage data,BP neural network model is constructed.In which,10 major leakage factors were selected to carry out neuron classification assignment,and training and test correction were carried out to test model.The correction BP model was mainly used to predict the influence of the leakage of Yingyan reservoir on deep mining.Conclusions are as follows:（1）Ten leakage factors in BP network model,including of valley shape,seepage characteristics of the riverbed,hydrological characteristics,development characteristics of faults,anti-seepage characteristics,bedrock permeability characteristics and leakage of water head,water level of the watershed,the bedrock karst development degree and lithological features,were used as the effective neurons.Its predication result is consistent with the practical measured results,with the correlation coefficient of 0.99,indicating that this model can be used to predict the reservoir leakage effectively;（2）Yingyan reservoir leakage was 0.013m³/s and only its dam showed weak seepage.Which indicated that leakage of reservoir will not affect extension mining of LindaI bauxite mine.Finally,the third potential source of water inrush,surface water injecting to tunnel though the new channel of karst collapse area during deep mining of bauxite,is discussed.The karst collapse area partition was firstly carried out by using AHP and GIS technology.Then influences of surface water injected into mine tunnel on deep mining were predicted at two different conditions of intact and damaged composite aquifuge.Conclusions are as follows:（1）When mining extended to 1040m tunnel,the composite lower confining bed is still intact,and the area of subsidence prone area is 53.2%of the covering area.Once it was damaged,the proportion increased to 62.8%;（2）When lower confining bed was damaged,collapse prone areas can reach the nearby Sala river up to 380m,and even extended to the area of office building,dormitory,air compressor room and other buildings.These will cause serious water intrusion,poured into the ground confluence,severely damaged the structure of buildings,endanger the safety of mine production and personnel.Therefore,protecting the integrity of aquifuge is important for safely deep mining and water prevention of Lindai bauxite area.Acooording to the above conclusions,this study supplied two sets of development scheme for deep mining in Lindai bauxite mine,including of extending existing shaft（I）and extending the existing blind incline shaft（II）.Based on compare analysis of the amount of construction projects,hydrogeological factors,methods and technical measures to prevent water,the amount of construction and construction difficulties,and the safety risks of underground water control,it was concluded that the mineral resources below 1190m tunnel in Lindai bauxite area can continue minging,and II"original shaft plus blind inclined shaft"development scheme is suggested as the preferred scheme for mining to 1140m tunnel in Lindai bauxite area.These retrieved167.76×10⁴t deep bauxite resources that was almost abandoned.This study not only has significant social and economic benefits,but also provides reference for deep mining and water prevention in the similar type of mines in the world.