Activation Seepage Mechanism On Structural Fracture Zone Of Coal Seam Floor In Mining Above Aquifer

With the coal mine extension mining, coal seam floor water inrush has become one of the majorhazards that threaten the safety of mine production. Water inrush from structural fracture zone isthe main form of mine water disasters. The study of seepage mechanism and activation ofstructural fracture floor during the mining process is of great significance for the prediction andprevention of mine water disaster. Therefore, with laboratory test, theoretical analysis and fieldmeasurement used comprehensively, the formation mechanism of fracture fissure zone activationinduced water inrush channel and the seepage mutation law during mining above confinedaquifer was investigated deeply. The results were as follows:The permeability change at different stages in rock failure process and relationship with theevolution of internal micro cracks were analyzed by the research experiment on micro seepagecharacteristics of rock fracture. With the variation of permeability following with deformationand the correlation between permeability and stress investigated, deformation law and varianceof permeability of plastic soft rock and brittleness hard rock was obtained in complete process ofstress and strain. According to the analogy and development of the failure mechanism andintrinsic permeability of brittle rock, combining with rock statistical strength and renormalizationgroup theory, the expression used to forecast strain on critical destructive point of rock wasderived on basis of probability function used to describe bearing capacity of rock specimen.According to the common mechanical characteristics of different water inrush mode, theprocess of fault water inrush was divided into two parts: water inrush preparation and activation.According to different mechanism of water inrush, the power of water inrush came fromhydrostatic force and hydrodynamic force. According to main influence factors of water inrush,the fault water inrush was classified into loose fault water inrush, dense filling fault water inrushand intermittent joint fault water inrush. The average water consisting strength of complete rockand fractured rock in coal bed was obtained through in-situ pressure percolation test. Afterwardseepage prevention characteristics of floor analyzed, effective aquiclude under floor was raisedto evaluate condition of seepage prevention in fault zone.By laboratory simulation test, we proposed the seepage evolution process, pore flow to fissureflow then to pipe flow, to signify the seepage process in fault zone. It is drawn a conclusion thatthe loss of filling particles in fault zone is the basis of fault water inrush quantity and change ofthe seepage type. The result of field water injection test came to the conclusion that the seepagefailure of structural fracture zone was the premonition of the floor water inrush. The structuralfracture zone activation induced water inrush, the important stage of floor water damageprevention, essentially was that the floor was seepage fractured. Considering the effect of different mechanical properties of medium in the fault zone andexternal mining disturbance, using the catastrophe theory, we established of fault activationinduced instability nonlinear model and derived necessary and sufficient mechanics criterion ofinstability and critical pressure of water inrush. From the non-linear perspective, the externaldisturbance conditions induced fault water inrush was divided into critical perturbationdisturbance and former strong disturbance. On basis of this, with correlation between faultactivation induced water inrush from coal seam floor and external mining disturbance analyzed,mechanism of fault activation induced water inrush under effect of external disturbance wasrevealed.Finally, the experimental and theoretical results were applied in field test to examine theapplicability of the evaluation method of water resisting strength and fault activation catastrophetheory model. It provide theoretical basis for the water inrush assessment of coal seam floorabove confined aquifer under the effect of structure in mining.