1. Introduction
Longwanggou Coal Mine is located 120km east of Ordos City, Inner Mongolia Autonomous Region. The administrative division is under the jurisdiction of Xuejiawan Town, Zhungeer Banner, Ordos City, with an area of 51.149km2 and a mining elevation of 1100-575m. The measured elevation of the Ordovician limestone water (hereinafter referred to as Ordovician water) in the minefield is 870m, and the west of the 870m contour of the minefield (including the first mining area) is all in under pressure mining situation.
61601 working face is located in the under pressure mining area, and is threatened by both the floor Ordovician water and the roof sandstone water. Ordovician water is extremely rich, and the replenishment water source is stable and sufficient. The thickness of the floor water barrier is 6.16-28m, and thinning zone may exist. With a mining height of 24m, the mining effect has a greater damage depth on the floor. Two gate entry and the middle of the working face are located in the stress concentration area, subject to shear stress, which has huge possibility of water inrush from the bottom. In the roof, water-conducting fissure zone has a large development height and conducts multiple layers of aquifers, which brings potential safety hazard to the layout of the later mining.
2. Solution
CCTEG Xi’an Research Institute uses underground directional drilling technology to investigate the water richness of the roof and floor, development of the water-conducting structure of the bottom water-proof rock layer, and carry out grouting transformations on the water-rich abnormal areas. The borehole can also be used for water drainage in water rich sandstone. The project helps ensuring the smooth and safe mining of Longwanggou Coal Mine.
3. Construction situation
This drilling project set up 2 drilling sites in the 61601 working face, and construct 5 directional drilling boreholes with total footage of 4,089m, including 2 roof boreholes, 3 floor boreholes. The deepest borehole reached 831m.
4. Achieved accomplishment
This project is an engineering case in the mine water exploration & release and the reconstruction & reinforcement of the working face floor. The quality of the construction project is qualified, the actual drilling holes meet the design requirements, and the original data records are complete, accurate and reliable. The exploration infers that the roof sandstone water storage of 61601 working face and the water output of Ordovician water from the floor are less than expectation. No large-scale abnormal geological structure was encountered during the drilling process, which provides a reliable basis for the layout and safe mining of the 61601 working face.
5. FAQ
Q1: Can the survey results of this project directly determine the hydrogeological conditions of the roof and floor of the working face?
A: Directional drilling does not expose the entire area, and the control range is limited. The roof drilling alone cannot conclude that the sandstone water content in the entire roof area of the 61601 working face is low, and there may still be rich sandstone water in some areas. It can be concluded from the effect of water pressure test before grouting to reform the floor that although the floor of the 61601 working face has less water produced from the floor, the floor sandstone layer is cracked. In view of the fact that the constructed floor hole can effectively indicate the formation and water content, but the drilling control range is limited, so there is a possibility of abnormal structures (and fissures) conducting Ordovician water in the areas not covered by the drilling.
Q2: In order to better ensure the layout and mining of the working face, how to strengthen the exploration?
A: It is recommended that the mine company observe the abnormal conditions of various water outflows in the working face and borehole control area in real time, and use certain geophysical and drilling methods to reconfirm if necessary. In the later mining of the working face, water quantity observation, water temperature observation, and water quality analysis should be strengthened, and safe drainage measures should be strengthened to avoid serious consequences.
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