Spatio-temporal Variation Of Fractures In Overburden Due To Mining And Risk Assessment Model For Water And Sand Inrush

There is a scientific problem when mining under sand aquifers,that is the spatio-temporal variation of stress amd fractures in overburden and its water and sand inrush risk assessment due to mining.In order to solve the scientific problem,a series of studies were carried out in this paper.Based on scale model tests,information entropy theory and spatio-temporal visualization analysis method,the spatio-temporal variation of stress amd fractures in overburden due to mining have been analyzed.The criterion of the fractures in overburden due to mining and their variation were established by combining with information entropy and fractal geometry theory.Finally,based on GIS and entropy,a spatial multi criteria decision making model was proposed to evaluate the risk of mining under sand aquifers and was validated with a case study,which was the Quandian coalmine in Henan Province,China.A new geographic information system(GIS)-based spatial multi criteria decision making system was developed.The main results are as follows:(1)A Space-time Cube visualization model is established to analyze the characteristics of stress in overburden due to mining.An engineering geological model is established according to the engineering geological condition of Panel 11050 in the Quandian coalmine.The stress of overburden is monitored by using the scale model test.Based on system science,information entropy theory and spatio-temporal data model,a stress entropy is proposed,a Space-time cube of stress model is established,and a trend analysis is applied.Characteristics of spatio-temporal variation of stress in overburden during mining process are determined.(2)A quantitative criterion is established to determine the spatio-temporal state of the amd fractures.The spatio-temporal variation of fractures in overburden is represented by using the scale model test and image processing technique.In accordance with the information entropy,a fractured entropy is proposed to quantitatively describe the direction or degree of propagation of the fracture,and the variations of fractured entropy of mining-induced overburden versus mining distance is calculated.Based on fractal geometry theory,the fractal dimension of fractures is calculated.The spatio-temporal difference of fractures in overburden due to mining is calculated,the quantitative criterion of the fractures is established to determine the spatio-temporal state of the fractures.(3)The variation of fractures in overburden due to ascending and descending mining with repeated mining are obtained.The variation of fractal dimension of overburden due to ascending mining is described as “saddle-shaped”,however,it can be described as “ladder-shaped” in the overburden due to descending mining.(4)A spatial multi criteria decision making model is proposed to evaluate the safety of mining under sand aquifers.Based on GIS and information entropy,a decision criterion system which contains the main criteria that determine the risk of underground mining under sand aquifers is proposed by considering the geological and hydrogeological conditions: sand aquifers,geologic structure,aquiclude,mining-induced overburden,mining activities.A complexity index is proposed to evaluate the degree of complexity of coal mine faults based on GIS,weighted linear combination,analytic hierarchy process and the fractal theory.The degree of complexity of coal mine faults is evaluated.A method based on multiple regression analysis and information entropy is proposed to predict the height of the water conducting fractured zones.A risk index is proposed to evaluate the risk of water and sand inrush in mining-induced overburden.And the decision result has been classified into five hazard region according to natural breaks method provided in GIS as a means of data classification.A sensitivity analysis is applied to evaluate the local changes of each criterion and how the selected criteria affect the risk index.A new GIS-based spatial multi criteria decision making system is developed,the risk assessment of water and sand inrush in mining-induced overburden can be decided in a second.