Mechanism Of Fault Reactivation-Induced Disasters During Coal Mining Above High Water-Pressure Confinedaquifers

Deep coal mining engineering get more chances to encounter high water-pressure inconfined aquifers. This dissertation focuses on the problem of a high water-pressure of nearly13MPa in the Ordovician limestone aquifer, in the Xingcun coalmine, Shandong Province. Itis well known that high water-pressure could lead to groundwater inrush easier from faultreactivation, which may cause serious coalmine disaster. Therefore, the research on themechanism of fault reactivation-induced disasters during coal mining above highwater-pressure confined aquifers has a great significance for the prediction and control ofcoalmine water disaster.In this dissertation, geological analysis, physical testing and theoretical analysis wereadopted to carry out a detailed study on the mechanism of fault reactivation inducedgroundwater inrush while coal mining above high pressure confined aquifers and get thefollowing results.(1) This dissertation points out that groundwater inrush from seam floor faultreactivation has the characteristics of hydraulic splitting and establishes a groundwater inrushrisk index evaluation method in fault reactivation based on entropy weight method andmultiple-source geological information fusion technology. The common phenomenon of faultreactivation after groundwater inrush from coalmine floors were summed up after analysissome typical accidents. These phenomena comply with hydraulic splitting characteristicsunder natural dynamic forces. Based on several typical groundwater inrush accidents, themain cause factors of groundwater inrush from fault reactivation were identified, whichinclude the aquifer, fault and aquifuge factors. Single factor analysis method was used toidentify the main ten evaluating indicator factors. At the same time, the weights of tenevaluating indicator factors were determined with using entropy weight method (EWM) ininformation theory. Then, the GIS platform was introduced to set up information layer andspatial properties database of the ten evaluating indicator factors, which were collected,stacked and analyzed with using multi-source geo-information fusion technology. After thatbased on multi-level, EWM and multi-source geo-information fusion technology, acomprehensive evaluation value of the evaluation grid cell was solved and characterized bythe groundwater inrush risk index. As a result, the figure of risk distribution was given.Particularly, the control measures for different risk area were promoted. Agroundwater inrushrisk comprehensive evaluation and risk index partitions were given for Panel E3206inYanzhou coalmining area.(2) Permeability characteristics and influencing factors were pbtained by series physicalsimulation tests of a fault with filling under high confining pressure and high cell pressure. A large number of physical tests were carried out under triaxial condition with a high cellpressure and a high permeability pressure gradient. The results show that the permeabilitycoefficient of fissure fillings and their contact surfaces with wall rocks increased aspermeability pressure gradient increases at a low confining pressure and cell pressure.However, at high confining pressure and cell pressure, the permeability coefficient of fissurefillings and their contact surfaces with wall rocks increased as permeability pressure gradientincreases at beginning. Then the permeability coefficient of fissure fillings will keep stable.Once the water-pressure raised a high level, the permeability coefficient of fissure fillingswould decrease. The main reason of this phenomenon was the high water-pressure adds aspecial infiltration load to stress field.(3) The mechanism of hydraulic fracturing induced fault reactivation was explained fromgroundwater dynamics and rock mass mechanics. Theoretical analysis, especially, theelastoplastic mechanics theory and groundwater dynamics theory were introduced to calculatethe permeability coefficient which contains stress field parameters. Based on coupled analysisof stress field and seepage field, the minimum principal stress and the maximum principalstress influence the aperture of a single fissure. The changing of aperture of single fissure wasthe main cause of permeability changing. As a result, the possibility of groundwater inrushaccident steeply increased. Moreover, rock mechanics and fracture mechanics theory wereused to set up a formula to calculate the length of fissures after hydraulic splitting.To sum up, based on the above research result, the original state and reactivation state offault zones were shown. The mechanism of fault reactivation-induced disasters during coalmining above high water-pressure confined aquifers is the result of the coupling effect ofseepage field and stress field, and the key action is the hydraulic splitting of high pressurewater in confined aquifers.