Study On Mechanism And Control Technology Of Mining Water Disasters Under Loess Gully Runoff In Northern Shaanxi

With the focus of China’s coal exploitation shifted to the northwest, new characteristics of coal mining disasters crossing loess gully appeared due to the interactive effect of criss-crossing loess gully landform with shallow buried and thin bedrock coal mining conditions, especially under the effects of the intermittent surface runoff even heavy rain, forming a complete disasters chain that shallow gravity destruction in loess gully areas-accelerating soil erosion-mining water(and sand) inrush.In this study, taking Hongliulin coal mine that located in loess gully areas of northern Shaanxi province as an example and Kentieling drainage basin in the coal mine as the main research object, based on comprehensive hydrogeology and engineering geology survey, theoretical analysis, situ tests, indoor tests, numerical simulation analysis, model similar simulation analysis and engineering practical application, mechanism and control technology of mining water disasters under loess gully runoff in northern Shaanxi were systematically analyzed, and preliminarily guiding the engineering practice. The main research results have been displayed as follows:(1) Based on ground drilling, water injection test, water pressure test, color drilling television, empirical formulas and discrete element numerical simulation, and so on, the failure rule of overburden with coal mining under loess gully were comprehensively researched. By combining the requirements of the water proof rock pillar height and sand proof rock pillar height in the regulations of buildings, water, railway and main well lane leaving coal pillar and press coal mining, the water disaster types with coal mining under loess gully runoff were classified into four types: water and sand inrush type, water inrush type, leakage type and security type.(2) Influences of dry density, volumetric water content and matric suction on permeability characteristics of unsaturated N2 laterite(Baode Fm. laterite) were detailedly studied by adopting Van Genuchten model on basis of measured results of soil-water characteristics curves(SWCC) under different dry densities. The results showed that with different dry density, unsaturated permeability coefficient is accelerated monotone increasing with increase of volumetric water content in semilogarithmic coordinates, unsaturated permeability coefficient is approximate linear related to volumetric water content, and permeability coefficient of dense unsaturated laterite is relatively sensitive to change of volumetric water content. With different dry density, unsaturated permeability coefficient is exponential function related to matric suction in semilogarithmic coordinates, unsaturated permeability coefficient is monotone decreasing with increase of matric suction, also expressing that permeability coefficient of dense unsaturated laterite is considerably sensitive to change of dry density.(3) The types and mechanisms of gravity destruction in loess gully areas were analyzed in the present study. Subsequently, the influencing factors of gravity destruction such as slope degree, slope aspect, geotechnical properties, and rainfall were comprehensively considered in raising the calculating formula for possibility coefficient of gravity destruction under the influence of multi-factor. Finally, taking Ken Tieling drainage basin within Hongliulin mine field for example, the possibility coefficient of gravity destruction of loess slope and laterite slope occurs under 10 mm rainfall were evaluated.(4) Based on the mechanical analysis of single sand particle, the mechanism of water and sand inrush of sand layer with coal mining under loess gully runoff was proposed. By controlling the width of structural surface and using self-designed test equipment, the types and mechanisms of the seepage deformation and failure of the unconsolidated soil layers across the caving zone and water flowing fractured zone within overburden were studied. The results show that the higher the clay content is, the higher the critical hydraulic gradient for water and sand inrush is. When the clay content is high, the seepage deformation failure mode of soil sample is water seepage-piping-water and sand inrush. When the clay content is low, the seepage deformation failure mode of soil sample is direct water and sand inrush. With water and sand poured out of the structural plane, the structural plane is plugged by larger and clay particles, the periodic water and sand inrush is appeared during the experiment, and the critical hydraulic gradient is increased exponentially with the water and sand inrush times. The shape of funnels caused by seepage deformation and failure of soil layers is related to the properties of soil sample.(5) With the proposed water disaster types with coal mining under loess gully runoff, differentiated and systematic control technology for water disasters were put forward, namely, comprehensive control technology of the hydrodynamic conditions and the flow of sand source, and supportingly apply to different types of water disaster areas in the gully. This water disaster control technology was applied to working face 15207 of southern first panel in Hong Liulin coal mine, and realizing mining safely over the gully.