Study On Risk Assessment Model Of Water Inrush From Shallow Coal Seam Roof Based On Spatial Multi-criteria Decision Making

Ordos Basin coal resource is abundant.The coal seams in some mining areas are shallow coal seams.The immediate roof aquifuge of the coal seam is thinner.The waterconducting fractured zone produced by coal seam mining can easily penetrate the overlying bedrock aquifuge,entering and destroying the aquifer,resulting in the roof water inrush diaster of the coal mine,which seriously threatens the normal production of the mine.This paper takes the shallow coal seam of Jinjie coal mine in the northern Ordos Basin as the study object,and takes the 31115 working face that is being mining in the mine as the research area.First,the hydrogeological structure and characteristics of the research area are studied.Then,the development height of the water-conducting fractured zone in the northern mining area of the Ordos Basin was predicted by using the method of multivariate statistical analysis and information entropy,and the height of the water-conducting fractured zone was measured and verified by the drilling TV.Then,combined with spatial multi-criteria decision making and GIS technology,the risk assessment of water inrush from the shallow coal seam roof in the research area was carried out.At the same time,the sensitivity analysis method of OAT is used to analyze the weight of the assessment criteria.Finally,the Model Builder in Arc Map was used to bulid a model for water inrush risk assessment from the shallow coal seam roof in the research area,which can quickly realize the regional prediction and risk assessment of the roof water inrush in the research area.The main research work and conclusions are as follows:(1)Through thin slice identification and mercury porosimeter method,it was found that the clay content(average 25.5%)in Yan’an formation sandstone of Jurassic is much higher than that in the Zhiluo formation sandstone(average 4%).The Zhiluo formation sandstone is mainly composed of intergranular and intercrystal pores which is larger than 10μm,with pores accounting for 61.68%.The confined water head of the aquifer is about 66.30 m,with a certain pressure head,and a large number of gravity water in the pores moves freely under a certain confined water head.Yan’an formation sandstone is mainly composed of intracrystal pores,intergranular and intragranular pores which is less than 10μm.This type of pores accounts for 78.02%.This pores contain bound water and a certain amount of gravity water.(2)A method for predicting the height of the water-conducting fractured zone in the northern Ordos Basin based on multivariate statistical analysis and information entropy is proposed.Compared with other standard empirical formulas,the predicted value is closest to the measured value,the mean absolute percentage error is 15.38%,and the normalized root mean squared error is 13.39%.Taking the 31114 working face of Jinjie coal mine as an example,the spatial characteristics of the water-conducting fractured zone in the study area are analyzed by using GIS technology,and the predicted height of the water-conducting fractured zone in the study area is 49.20 m to 54.54 m,and it is expected to be low in the middle and high on both sides.Then it was measured by a borehole TV,and the measured value is greater than 42.4m,while the predicted value is 49.6m,which verifies the feasibility of this method.(3)A system of assessment criteria for the water inrush risk from shallow coal seam roof based on "channel-source-mining" is proposed.The assessment criteria are selected and determined by three factors: water inrush source,water inrush channel and mining.Then the criteria were standardized,and the weight of each criterion was calculated based on information entropy.In the water inrush source criterion,water yield property of aquifer is 0.41313,the permeability of aquifer is 0.37663,and thickness of aquifer is 0.31024.In the mining criteria,the buried depth of coal seam is0.44776,and thickness of coal seam is 0.55224.According to the hierarchical structure,the weight of the water inrush channel criterion is 0.30131,the water inrush source criterion is 0.57830,and the mining criterion is 0.12039.(4)A water inrush risk assessment model from the shallow coal seam roof is established,and the water inrush risk index is used to predict and evaluate the water inrush risk in the research area.The Jenks natural breaks method is used to classify the predictive results,and corresponding treatment measures are proposed for different water inrush dangerous areas,and the mining verification was carried out.The Model Builder in Arc Map was used to bulid a model for water inrush risk assessment from the shallow coal seam roof in the research area,which can quickly realize the regional prediction and risk assessment of the roof water inrush in the research area.(5)The sensitivity analysis method is used to quantitatively evaluate the influence of the fluctuation of the criterion weight on the assessment results of water inrush risk.Taking the mean of the absolute change rate of the pixel assessment results as the assessment index,it was found that the sensitivity order of criteria is: overlying strata failure height>water yield property of aquifer>permeability of aquifer>thickness of aquifer>thickness of coal seam>buried depth of coal seam,in which the overlying strata failure height has the largest weight and the highest sensitivity,while the buried depth of coal seam has the smallest weight and the lowest sensitivity.