Mechanism Of Water Inrush On Faults Of Coal Seam Floor And Prediction Of Dewatering Rate From Karst Aquifers In Beiyangzhuang Mine

The endowment characteristics of natural resources determine that coal is the main energy source in our country,and it is difficult to change this energy pattern in a long period of time in the future.Water inrush is the second largest disaster of coal mine after gas accident in the production process of coal mine.There are many water-filling aquifers in the roof and floor of coal seam,especially the karst water-filling aquifer in the floor,and a lot of water inrush is closely related to it.Groundwater in these aquifers often enters mines through fault and other water inrush channels.This show it is of great significance to protect the life of miners and the safety of property through studying the identification of mine water inrush source and the water inrush mechanism of faults.For the mine with karst water as the main source of water filling,it is the premise of safe production to dynamically predict the rate of dewatering from karst aquifer.Further discussion on the treatment of mine water and resources utilization are of great significance to the protection of water resources and ecological environment.This paper takes a water inrush case as the background,which occurred in the second mining area of Beiyangzhuang coal mine in Yuxian county,Hebei province in September 2014.Firstly,the hydrogeological conditions and water filling sources are systematically analysed.Secondly,hydrogeochemistry theory and Fisher discriminant analysis method are used to identify the source of the water inrush.Thirdly,The fluid-solid coupling numerical model of typical section with the fault zone is established,and the mechanism of water inrush of fault activation induced by bore dewatering is revealed by means of numerical simulation.Fourthly,the numerical model of karst water movement in the region is established,which dynamically predict the dewatering rate for safety mining in the second mining area.Finally,the paper propose the treatment technologies of mine water which is consist of karst water and the ways of resources utilization.The main research contents and results are as follows:?1?Based on the analysis of geological conditions of Beiyangzhuang mine,the lithology,structure,permeability and water yield property of each water-filling aquifer?aquifer group?are studied.The hydraulic connection between the water filling aquifer?aquifer group?is ascertained through the study of aquiclude lithology,thickness and distribution regularity,then the supply,runoff and discharge conditions of water filling aquifer?aquifer group?are analysed.Furthermore,the hydraulic connection among the water-filling aquifer?aquifer group?is determined by the lithology,thickness and distribution of the aquiclude,and the recharge,runoff and discharge conditions of the water-filling aquifer?aquifer group?are analyzed.On this basis,the characteristics and types of the water filling water source,the type of the water filling channel and the characteristics of the water filling strength are determined.The results show that the hydraulic connection between the water-filling aquifer?aquifer group?is controlled by sedimentary structure of the stratum,there is no hydraulic connection between the karst water and the fissure water,and the hydraulic connection between the fissure water and the pore water is not close,and only the hydraulic connection occurs in the section with skylight.Water filling sources are karst water,fissure water and pore water.The water filling channels mainly are fault,and then are broken zones caused by mining,broken zones caused by confined water and water-conducting fractured zones.The water filling strength of karst water is the greatest.?2?In this paper,the test results of 33 water samples form 3 water filling sources are collected,witch include 8 pore water samples,11 fissure water samples and 14karst water samples.Their chemical compositions are pH,TDS,HCO₃^-,SO₄^2-,Cl^-,Na⁺+K⁺,Ca²⁺and Mg²⁺.According to the test results,the minimum value,the maximum value and the average value of the water chemical components of each water-filling source are calculated,and the hydrochemical characteristics of each water-filling source are analyzed according to the statistical results.Piper three-line diagram is used to classify 33 water samples from 3 water filling sources and 3 water samples of water inrush points.Meanwhile,the hydrogeochemical effect of each water-filling source is analysed,and the similarity is compared between the water chemical types of water inrush points and water chemical types of water filling sources.Moreover,7 water chemical components,TDS,HCO₃^-,SO₄^2-,Cl^-,Na⁺+K⁺,Ca²⁺and Mg²⁺are selected as identification indexes,33 water samples of the three known water sources mentioned above are used as training samples,and the identification model of water source of mine water inrush is established based on the Fisher discriminant analysis.Importantly,the discriminant functions and their recognition contributions are calculated by using SPSS19 software.The validity of the discriminant function is evaluated according to the given significant level,and the hydrochemical indexes which contribute a lot to the identification are determined.The key is to identify the source of water inrush according to the discriminant function values of the training sample and samples of the water inrush point using the shortest distance as the recognition criterion and to use the discriminant function to identify the water source type of the training sample to further test the validity of the discriminant function.The evolution law of the hydrochemical types of karst water near the water inrush point is analyzed.The variation of the flow field of karst water during the process of dewatering to water-inrush is inferred.In addition,the source of water inrush is also identified according to groundwater regime and groundwater temperature,and the results are compared with those obtained by hydrochemical method.Finally,the results show that the characteristics of water chemistry of water sources are different,which provides the condition for water chemistry to identify the source of water inrush,and the type of water chemistry of water inrush point is very similar to that of karst water.The result of water inrush identified by Fisher discriminant analysis method is karst water,which is consistent with the result of groundwater regime and groundwater temperature identification,and identify results are reliable.The affection of water inrush is very strong for karst water flow field,and the relatively new karst water comes from distant runoff in the process of water inrush.?3?This paper summarizes the forming conditions of water-rich fault,water-storage fault,water-conducting fault,water-blocking fault and water-barrier fault from the mechanical types,geometric characteristics,lithologic structure,cementation condition,surrounding rock lithology and hydrogeological characteristics.The characteristics of water filling deposit for each type of fault mentioned above is discussed.The hydrogeological types of faults are divided in the Beiyangzhuang mine.According to the results of clay mineral analysis,physical and mechanical tests of rock mass,the engineering geological characteristics of rock mass are analyzed.Based on the analysis of the relationship among dewatering,the F_t fault zone and water inrush.the coupled mathematical model of stress-seepage field is constructed based on the ideal elastic-plastic theory and Biot consolidation theory,,and two fluid-solid coupling numerical model are constructed by using FLAC³DD software,including the natural conditions and disturbed condition on dewatering.The softening and disintegration effect of karst water on the fault zone is characterized by reducing the mechanics parameters of fault zone,and the negative exponential relationship between the average effective stress and the permeability coefficient is considered in the model.The stress,deformation and seepage characteristics of the fault zone under natural and disturbed conditions are simulated,respectively,and the mechanism of water inrush of fault activation is revealed by comparison their changes.Meanwhile,the time of water burst?inrush?to roadway can be determined according to the water pressure of monitoring points.Finally,the results show that the low strength and strong softening of fault zone and surrounding rock are the fundamental causes of water inrush,the karst water form bore softens the fault zone is the inducement of fault water inrush,and the fault zone is a weak zone under the natural conditions.The deformation is concentrated in the position where the fault zone intersects with the karst aquifer group,which creates conditions for water inrush.Karst water form dewatering bore softens fault zone,which transforms into disturbed area later,this effect significantly reduces the maximum principal stress,increases shear deformation,increases volumetric strain,increases horizontal displacement.Meanwhile,the disturbed area of fault zone moves from its center line towards to the surrounding rock.These factors increase its permeability,which leads to the seepage of karst water along the disturbed area of fault zone.The karst water in the fault zone and dewatering hole soften the surrounding rock of the dewatering hole,so disturbance zone of the surrounding rock is formed.The disturbance zone of surrounding rock occurs shear failure under the action of water pressure and stress,which increases its permeability,and makes karst water flow rapidly along the disturbance area of surrounding rock,and water burst?inrush?occurs through the coal wall of roadway.?4?The characteristics of karst water system are systematically analyzed from five aspects:geological characteristics,boundary conditions,karst burial types,karst development characteristics and karst water cycle.The boundary conditions are identified by geological data,pumping test and mine water inrush data,the types and characteristics of karst development are analyzed by the statistical characterization of the hydraulic conductivity and the specific yield,and the seepage model of karst medium is determined.The recharge conditions of karst water are determined by karst burial type and boundary characteristics.According to the characteristics of karst water system,the mathematical model of karst water movement is established.Based on the mathematical model,the numerical model of karst water system is established by using GMS software.Based on the regime of 5 observation holes of karst water in the process of the dewatering and water inrush,the parameters and its hydrogeological zoning of the model are identified.The relative root mean square error?RRMSE?is used to evaluate the reliability of the prediction model,and the sensitivity of hydrogeological parameters is evaluated by sensitivity index method?SI?.Two dewatering schemes,natural conditions and local grouting are designed in the second mining area of Beiyangzhuang mine according to the risk evaluation of water inrush.The critical water level of the two schemes is calculated by the method of water inrush coefficient,and the dewatering from the karst aquifer group is predicted dynamically according to the mining plan.Finally,the results show that the karst water system is a relatively independent groundwater system.The karst water movement is generalized into heterogeneous anisotropic two-dimensional unsteady flow.the numerical model of karst water based on the equivalent pore medium method is reliable.The sensitivity of hydraulic conductivity in the x direction is far greater than that in they direction and the water storage coefficient.Both schemes can realize safe mining,but local grouting can reduce the rate of dewatering in the mine,which is beneficial to the protection of karst water resources.?5?In Beiyangzhuang mine,most of mine water sources are karst water,and the type of mine water quality is suspended mine water.According to the water quality and source characteristics of mine water,first,the sewage diversion is carried out in the underground,and the clean water is directly utilized and sewage is disposed.The order of sewage treatment is goaf purification,surface clarification and disinfection,iron removal,volatile phenols and fluoride removal.The utilization channel of mine water is Beiyangzhuang mine,Yuxian county,Datang power plant,agricultural irrigation and reservoir of Huliu river,respectively.According to the principle of superior effectively use of high quality water and water supply by different quality,and the demand of each user for water resources,mine water sources are optimized configuration.Finally,the results show that mine water has utilization potential and brings about significant environmental and social benefits.