Comprehensive goaf treatment of coal mining subsidence area
1. Introduction
This project is located in the area of renovation of shanty district, Rencheng, Jining. The scope of treatment is shown in the figure below. The population is dense, the mining geological conditions are complex, and the disaster characteristics of strip goaf with buried depth of 520 ~ 580m feature the long-term, concealed, complex, sudden and unpredictable properties. Complicated conditions bring difficulties in accurate survey and treatment. This kind of strip goaf treatment is the first example in China, with difficulties in treatment. If no treatment is made, it will pose a great potential safety hazard to the safety of surface buildings (structures) in the later period.
Schematic diagram for the range of the project governance
2. Treatment solution
In view of the complex geological, mining and construction conditions of the project, the advanced all-digital high-precision 3D seismic exploration technology, project evaluation management (PEM) system and vertical seismic profile technology (VSP) precise exploration technology, borehole digital holographic imaging technology and 3D sonar modeling technology were used to carry out accurate exploration in the goaf subsidence area. On the basis of mastering the caving shape and basic characteristics of strip goaf in detail, the pier and pillar goaf treatment scheme was adopted in a targeted manner. Innovative use of directional drilling technology, construction waste recycling crushing, mixing, transportation and backfilling technology to treat the goafs, and distributed optical fiber dynamic monitoring technology can achieve the whole life cycle safety monitoring of ground development projects.
3. Construction situation
There were 115 vertical grouting boreholes and 3 directional boreholes completed in the first-stage treatment area of the project, and 110,000 m3 of cement fly ash slurry and 473m3 of high-concentration slurry of construction waste recycled materials were completed. The goaf is 52,400 m2; the specific location is shown in the figure below.
Schematic diagram for the range of governance in the project phase I
Automatic grouting station
4. Achieved accomplishment
According to the mature testing method of engineering treatment effect recommended by relevant domestic codes and standards, this project adopted such methods as inspection hole coring and geophysical exploration to test the engineering effect; grout core were taken out at different depths in the target layers of grouting treatment in different areas, and the wave velocity, bulk density and lateral resistivity of the treatment layers increased greatly, which indicated that the grout filled and strengthened the goaf cracks in the grouting target layers effectively and ensured the engineering effect.
Grout core taken from the depth of 519m in borehole A-N10
Grout core of in the fissures of a coal seam
Grout core in the fissures of the cover rocks in goaf
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