1. Project Introduction
With an average coal thickness of 10.68m, No. 5 coal seam is the main mined coal seam in Wangwa No.2 Mine in Ningxia. The length of rock roadway in the tail entry is 338m, which is located in the weathering zone of the coal seam. The head entry of the coal seam has normal geological conditions. However, the development morphology of the weathering zone will seriously affect the mining efficiency and the secondary layout plan of the working face.
Fig 1. Estimated weathering zone in the working face
2. Treatment and solution
Adopting in-seam seismic exploration technology, difference in amplitude attenuation coefficient and propagation velocity during the propagation of the waves in coal seam was used to explore the development form and location of the weathering zone. It has the advantages of long exploration distance, high accuracy, strong anti-interference ability, easy identification of waveform features, and intuitive final results.
Fig 2.Formation principle of in-seam seismic wave
3. Work situation
120 shot points and 222 geophones were deployed in the middle of the coal wall in the head entry, tail entry and interconnection. The distance between the adjacent shot points was 10 m and the distance between the adjacent geophones was 20 m. The whole exploration length was 2210m.
Fig 3.Working site of the in-seam seismic exploration
4. Achieved accomplishment
After the in-seam seismic exploration was conducted, development pattern of the weathering zone in the working face was identified. The weathering zone had a straw hat shape in the working face, with a strike length of about 410 m, an inclination of about 130 m, and a total area of about 24300 m2 (Fig.4). By redesigning the mining layout of the working face, the mining efficiency was effectively improved and the economic benefits highly increased.
Verification was conducted during mining process. In the redesigned working face, according to the results of the in-seam seismic exploration, the weathering zone has a strike length of about 120m, a dip length of about 60 m, and an area of 4870 m2 (the black curve range in Figure 5). From the mining data, the actual strike length of the weathering zone was 108m, the inclination was 58 m, and the area was 3484 m2 (the range of the red curve in Figure 5).
Fig 4. Survey result of the in-seam seismic exploration
Fig 5.Verification result during mining process
5.FAQ
Q1: Why do you use the in-seam seismic exploration technology to solve such kind of problems?
A: Seismic waves show strong differences in wave field characteristics such as propagation velocity and amplitude attenuation coefficient when they pass through different coal thicknesses. This difference has a strong regularity. The inversion of attributes can reflect the change in coal seam thickness.
Q2: What kind of work can your company do in this field?
A: Using the in-seam seismic exploration, we can also detect geological anomalies such as small faults, subsidence columns, coal seam bifurcation and thinning zones, goafs and abandoned roadways. It has a large exploration distance, high accuracy, strong anti-interference ability, easy to identify waveform characteristics, and the result is intuitive.
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