Research on Mechanism of Water Inrush Based on Mining Instability of Water-repellent Soil Layer in Shenfu Mining Area
Supervisor:zhang jie suo yong lu
The stability of"Sanztima laterite"aquifer is of great significance to the study of roof water inrush mechanism of shallow coal seam with thin bedrock in Shenfu mining area.The miero-fracture damage-healing mechanism,macro-intability-water inrush mechanusm and spatio-temporal response law between pore water pressure and roof watr inrush of water-proof layer under the combined action of mining stress field and seepage field play a key role in the study of roof w’ater inrush mechanism in Shenfu mining area.The solution of these problems can effectively reveal the roof water inrush disaster caused by the instability of water-proof layer.In this paper,theoretical analysis,geotechnical expetriment,two-phase physics and numerical simulation,engineering practice and other methods are used to study the mechanism of roof water inrush based on the failure and instability of water-proof layer.The main results are as follows:(1)Through the analysis of the geotechnical experiment,it is found that the ultimate shear strength of the soil-water barrier in Shenfu mining area will jump along with the change of the liquid index.From the point of view of hydraulics,physics and deformation,three characteristics of water-pcroof layer are put forward:1)water-proof characteristics:the morphological difference of the occurrence state of water-proof layer changing with burial depth,and its liquid index decreasing linearly with burial depth,which will cause its morphological change;2)physical characteristics:the depth difference of the intensity index of water-proof layer changing with burial depth.3)Deformation characteristics:the particularity of surface subsidence after shallow coal seam mining in thin bedrock-the difference of subsidence of water-proof layer.It can be used to explain the reasons for the increase of surface subsidence in Shenfu mining area,and the analytical solution of additional subsidence at each point in the main section of the water-proof layer in semi-infinite spa,ce is obtained.(2)Based on theoretical deduction and numerical calculation,the development law and healing evolution process of longitudinal fissures in water-proof layer are analyzed.The mechanism of longitudinal fissure development is analyzed by constructing seepage coupling equation of pore-fissure medium in soil layer,and the analytical solution of longitudinal fissure width is obtained.The concept of fissure healing degree is put forward to express the self-adaptive healing ability of soil by constructing the seepage coupling equation of pore-fissure medium in soil layer.The stress model of fissure healing is deduced,and the analytical solution of fissure healing degree is deduced.After fissure healing,the occlusion articulation zone will occur,which can make the soil units extrude and deform each other,and finally make the fissure medium combine into a compact bonding structure to restore the original soil permeability and water resistance.At the same time,it is found that the permeability of occlusion articulation zone is weaker than that of non-occlusion articulation zone,that is,soil.After the healing and compaction of layer fissures,it is possible to further enhance the water-resisting performance of some soils.(3)The viscoelastic dynamic model of the relationship between pore water pressure and dynamic mining in water-proof layer is established,and the analytical relationship between them is obtained.It is found that different mining intensities have different disturbance effects on water and soil barriers.When the mining intensity is high,the pore water pressure of overlying water-proof stratum in goaf will be distorted funnel,which is most serious at both ends of working face.When mining intensity is low,the pore water pressure of overlying water-proof stratum in goaf will fluctuate periodically and slightly without accumulation and rapid dissipation.There is a close space-time response relationship between the pore water pressure of the overlying water-proof layer and the water inflow from the roof of the working face.Due to the influence of mining and seepage,when the macro-longitudinal fissures in the water-proof layer are fully developed,the pore water pressure in the micro-upper layer will be distorted,and the water inflow from the roof of the working face will increase sharply.(4)Based on the convergence of water inrush case data and the discriminant analysis of theoretical model,it is found that the spatial and temporal range of water inrush from roof is closely related to the ratio of soil to mining.The ratio of soil to mining is relatively small and the soil is riveted shear failure after several cycles of pressure.In the roof water inrush accident,the ratio of soil to mining is relatively large,and the soil is"elliptical arc tensile failure".The critical soil-mining ratio of the two failure modes is 7-8.The two methods are the time relationship.First,the rivet shear failure is discriminated for the water-proof layer,and then the elliptic arc tension failure is discriminated for the stability of the soil layer,so as to predict the roof water inrush preliminarily.Evolution test of water inrush shows that when the ratio of soil extraction exceeds 14-15,the intact soil in the middle of the water-proof layer plays a strong water-proof role,and the cracks in the upper and lower layers of the soil will"self-heal"in the process of stress recovery and drainage.The larger the healing degree of the cracks in the water-proof layer,the smaller the permeability coefficient of the soil after healing,and a certain drainage phenomenon will occur.Its water-proof performance is contrary to that before destruction.However,the penetration and deformation characteristics further validate the occlusal articulation effect after fracture healing.(5)According to the influencing factors and characteristics of water inrush from shallow seam roof in Shenfu mining area,a prediction model of water inrush from shallow seam roof is established,which integrates qualitative and quantitative indexes.This model can not only classify and rank the single water inrush risk factors,but also accurately predict the comprehensive water inrush risk level and the water inrush risk point of the working face,which reduces the blindness and workload of the pre-mining water inrush prevention work,and provides a new way for water inrush prediction of shallow seam roof in northern Shaanxi.The feedback of the measured water inflow proves that the model not only accurately obtains the comprehensive water inrush level,but also predicts the coordinate positions of the dangerous points of water inrush,which enables the miners to focus on exploring the dangerous points of water inrush before coal seam mining,and greatly reduces the probability of roof water inrush accidents.Finally,based on AHP-GRA coupled prediction model and combined with Arc-GIS and MATLAB,the data visualization analysis of water inrush correlation degree is carried out in the mine field,and the distribution maps of water inrush correlation degree corresponding to five first-level indexes are obtained.The database of water inrush correlation degree of each point coordinate can provide an important reference for the formulation of water inrush prevention measures in each working face of the mine accurately.Starting from the coupling effect of mining disturbance and water seepage,taking the water-proof stability of water-proof layer as the key point,and taking the prediction and discrimination of roof water inrush as the target point,this paper studies the mechanism and prediction of roof water inrush disaster based on the destruction of water-proof layer.The research results enrich the content of the roof water inrush prediction research system in Shenfu mining area,and for shallow coal seam with thin bedrock under water-rich area.Safe mining has important guiding significance.