Prediction Of Inflow In Roof Of Working Face By Seepage-stress Coupling Model

Seepage exists naturally in two different kinds of media: porous medium and fracture medium. Continuous medium method simulating liquid seepage is generally suitable to porous geological bodies, groundwater simulation method commonly used at present is based on continuous movement of groundwater in geological bodies and is not certainly suitable to fractured rocks. Since the distribution and characteristics of fractures are considerably different from those of pores, if liquid seepage is mainly controlled by fractures, assumption of porous medium has difficulty in characterizing seepage of fractured rocks.When an aquifer exist around a coal seam, excavation of roadways and extraction of coal seam may induce redistribution of rock stress, particularly after extraction of coal seam, the equilibrium status of original stress in rocks of overlying strata and floor is destroyed, forming three zones: collapsed zone, fractured zone and bending zone, inducing variation of rock permeability. From the aspects such as hydrogeology, engineering geology, mining disturbance and rock mechanics etc, to study the seepage field and the evolution regularities of fracture network, the regularities of inflow induced by collapse and fracturing of roof at working face and their main inflowing factors, is very necessary for correctly understanding inflow mechanism induced by mining disturbance at working face, evaluating and predicting inflow and inflow volume at working face. The paper consists of tow parts studying the theory and application of prediction of inflow volume in roof at working face by seepage-stress coupling model.The first part focuses on theorical analysis and mathematical derivation for prediction of permeability of disturbed fractured rocks and inflow volume in roof at working face, derived and discussed characteristics of permeability in fractured rocks, studied stress field under mining disturbance, conducted numerical simulation for collapse process of overlying rocks during stopping at working face, studied the relation between stress field and seepage field. The coupling effect formed due to multual impact of seepage field and stress field in fractured rocks was represented by two following aspects: a. when seepage occurred in fractured rocks(i.e. when seepage field existed), seepage action( including static pressure and dynamic pressure) induced by groundwater seepage in fractured rocks would change the original stress status in rocks(i.e. stress field environment in fractured rocks); b.the change of stress status in fractured rocks would impact the structure of rocks, so changing the performance of permeability in fractured rocks, which was represented by variation of groundwater seepage field in fractured rocks.The second part of the paper studied water abundance characters of roof aquifer of coal seam and regularities of movement and destruction of disturbed overlying rocks on the basis of the actual problem of roof water encountered during extraction at working face 2301 in Yuyang mine, predicted the inflow volume at disturbed working face. From calculation of numerical simulation and empirical equation, the height of water-conducting fracture zone was 65 m, and the zone had developed into Zhenwudong sandstone aquifer, and mining directly connected the aquifer. In order to prevent water from phreatic aquifer in weathered zone of bedrock from coming into working face, water prevention pillars of 111.35 m height were left, while the distance from the roof of coal seam to the floor of aquifer in weathered zone of bedrock was 163.09 m, therefore safe mining could be realized. Through comparison with actual inflow volume, the calculation method was proved correct, providing basis for safe production of mine.Through theorical analysis and study of simulation test, on the basis of destruction characteristics of overlying rocks and variation of permeability characteristics due to mining, we subdivided for first time the fracture zone into network fracture zone, directional fracture zone and separated layer fracture zone, firstly proposed formula for calculation of water inflow at collapsed working face in consideration of water filling of multiple aquifers and elastically desaturation of aquifer. The calculation method is more accurate and more corresponding to the actuality.