Isolated overburden grouting filling method for coal gangue underground emission reduction

An isolated overburden grouting filling method for coal gangue underground emission reduction, comprising following steps:

• a, distinguishing, according to mining parameters and geological information on a coal mining face, key strata in an overburden;
• selecting, according to requirements for a surface subsidence control and a gangue filling processing volume, one of the key strata with a thicker thickness as a grouting filling key stratum, wherein a lower boundary of the grouting filling key stratum is a selected grouting filling horizon;
• b, selecting, from a roadway outside a terminal line of the coal mining face, a position as a drilling site;
• constructing an underground directional hole in a direction of the grouting filling key stratum from the drilling site, wherein a first drilling drill-hole of the underground directional hole is an inclined hole, a direction of the first drilling drill-hole is a direction of an open-cut off in the coal mining face, a trajectory of the inclined hole is spaced at a certain distance from a boundary of a water conducting fractured zone on the coal mining face;
• continuously drilling forwardly, after the underground directional hole enters the grouting filling key stratum, for a certain distance in the direction of the open-cut off in the coal mining face along a middle plane of the key stratum, wherein a drilling direction is parallel to an advancing direction of the coal mining face;
• subsequently inserting a high-strength casing, and completing a cementing of the first drilling drill-hole with a cement slurry;
• c, continuously drilling forwardly, along the middle plane of the grouting filling key stratum, a main hole, wherein a projection of a drilling trajectory on a horizontal plane is parallel to the advancing direction of the coal mining face, the main hole is inclined downward;
• stopping, when drilling the main hole to a distance of 50 m away from the open-cut off in the coal mining face, the drilling;
• d, constructing, starting from a drill-hole ended point of the main hole, a group of obliquely downward branch holes at regular intervals along an axis direction of the underground directional hole, wherein each group of the branch holes consists of one or more rows, and the rows are as backups for each other in each group, a drill-hole ended point of each branch hole is located below the lower boundary of the grouting filling key stratum, and above a top boundary of the fractured zone on the coal mining face;
• e, injecting, after completing the construction of all branch holes, a non-consolidated high-viscosity filler into the main hole and branch holes through an orifice of the underground directional hole to fill all branch holes and an interior of the main hole of the underground directional hole;
• f, injecting, when the coal mining face is mined at the drill-hole ended points of the branch holes in a first row of a first branch, a low-concentration gangue slurry into the main hole through the orifice of the underground directional hole according to an attenuation of a drill-hole pressure;
• continuously increasing, with the coal mining face passing through the branch holes in the first row of the first group, a slurry concentration and a grouting volume according to a change of the drill-hole pressure, thereby forming the grouting filling horizon;
• g, spreading, with a continuous mining of the coal mining face, fractures in the grouting filling horizon forwardly;
• communicating, when the coal mining face approximates to the branch holes in a subsequent row, the fractures in the grouting filling horizon with the branch holes in the subsequent row to form a communication channel of main hole-branch hole-grouting filling horizon;
• and
• h, continuously grouting, with the coal mining face being continuously mined forwardly, to the fractures below the grouting filling key stratum through the main hole, wherein due to an effect of a pressure, a lower caved and a fractured zone rock mass are squeezed downwards, and the grouting filling key stratum is supported upwards, thereby increasing opening degrees of the fractures, greatly increasing the grouting volume and processing the underground gangue, effectively supporting the grouting filling key stratum, and effectively controlling the overburden and surface deformation until the mining of the coal mining face is completed.