Safe mining method for water-rich gently inclined coal seam

A mining method comprising:

• preparing cut hole strips, wherein at positions that are located on two symmetrical sides of a coal seam central axis on a working slope coal seam, cut hole strips are divided along an open-pit mine advancing direction, and a width of the cut hole strip in the open-pit mine advancing direction is less than an annual advance, and wherein an overburden bench above a coal seam roof of the cut hole strip advances ahead to expose a coal seam in the cut hole strip completely;
• constructing a local drainage system, wherein at a junction of the coal seam in the cut hole strip and the overburden bench in an upper part, a trench below a coal seam floor is dug down as a dewatering trench, wherein, with the coal seam central axis as a middle point, the dewatering trench is arranged along the coal seam floor in a pseudo-inclined layout toward end slopes on both sides respectively to form a 0.5%~1% flow gradient, wherein a position near the end slopes on both sides is a low point, wherein a water collection pit in communication with the dewatering trench is separately dug at the low point, wherein in a position of the coal seam central axis, a trench below the coal seam floor is dug down along the open-pit mine advancing direction as a diversion trench, and wherein the diversion trench is in communication with the dewatering trench to form a "T"-shaped drainage structure;
• mining the cut hole strips, wherein the coal seam in the cut hole strip is divided for small-bench mining along the open-pit mine advancing direction, wherein a floor is exposed after the coal seam is mined, wherein, after a width of an exposed area that moves upward along the coal seam is more than four times a thickness of the coal seam, rubble is laid in areas of the dewatering trench and the diversion trench below the coal seam floor, and wherein a straw curtain or gauze is overlaid to form a dewatering blind trench and a diversion blind trench;
• performing run-of-mine coal cross-cut mining, wherein after the cut hole strip is completed, benches on both sides of the cut hole strip in an advancing direction are widened to form two cross-cut mining working faces, wherein the cross-cut mining working faces advance in directions of the end slopes, wherein the working slope coal seam is mined, and wherein the overburden bench in an upper part of the coal seam advances ahead of the cross-cut mining working face;
• constructing a continuous drainage system, wherein, as the cross-cut mining working faces advance constantly in directions of the end slopes on both sides, the coal seam floor is constantly exposed, the dewatering blind trench also extends synchronously towards both sides, and a construction position of the water collection pit also changes synchronously, but the cross-cut mining working face is always located at an end point position on a side of the dewatering blind trench near the end slope, and wherein staged diversion blind trenches in parallel with the diversion blind trench are spaced 100~200m apart on the coal seam floor and are in communication with the dewatering blind trench;
• constructing a bulkhead dam, wherein in a run-of-mine coal cross-cut mining process and in a goaf after the coal seam in the cut hole strip is mined, open-pit mine overburden materials are discharged and roller-compacted in layers along an edge of a side of the dewatering trench close to an inner dump, so as to form a bulkhead dam, and, in addition, a permeable material is backfilled between the working slope coal seam and the bulkhead dam as a permeable layer;
• performing an inner dumping follow-up, wherein after the bulkhead dam reaches a design height and when the bulkhead dam extends beyond widths of two open-pit mine lanes in the directions of the end slopes on both sides, with the coal seam central axis as a starting point, a conveyor bridge in communication with the inner dump and the working slope coal seam is constructed above the bulkhead dam, and, with the conveyor bridge as a starting point, the inner dump performs inner dumping follow-up respectively towards the end slopes on both sides and the open-pit mine advancing direction;
• and
• performing mining cycling, wherein when run-of-mine coal cross-cut mining reaches the end slopes, on both sides and the inner dump synchronously follows the end slopes, this round of mining ends and the permeable layer is recovered, and then a next round of cut hole strip is delimited, and wherein a next round of mining is performed based on the foregoing steps, so that mining is cyclically similarly.