1. Introduction
During excavation process of a roadway in a coal mine in Shanxi, a lithological anomaly section with a length of about 120 m was exposed. Based on the lithological and structural characteristics of the roadway, the anomaly was identified as a collapse column and was named X140. In addition, in the head entry and the tail entry, two breakpoints with a drop more than the coal thickness were exposed. Before the working face is mined, it is urgent to find out the subsidence column X140 and the entrance and return lanes to expose the breakpoints in the working face.
2. Treatment solution
The transmitted in-seam seismic survey technology was used to arrange shot points and geophones in the two entries in the working face, and utilize the characteristics of the amplitude attenuation and velocity changes that occur after the structure encounters the propagation of the channel waves in the coal seam.， which can determine position and size of the construction.
3. Work situation
Combined with the mine geological data, on the basis of the underground field survey, a survey line of 580m was set up in the intake lane while a survey line of 590 m was set up in the return lane. The detection range had relatively high ray density, with a minimum of 40 lines per unit cell and a maximum of 400 lines, which meets the requirements of imaging for in-seam seismic exploration.
4. Achieved accomplishment
The range of collapse columns X140 and CX1 explained by the in-seam seismic detection basically coincided with the drilling results. Fault CF1 explained by the in-seam seismic exploration even had higher accuracy after the mining verification.
Figure 1. Detection effect
5. FAQ
Q1: Can inseam seismic exploration explain collapse columns whose major axis diameter is less than 20 m?
A: The minimum diameter of the long axis of the collapse column successfully explained in the actual production process at this stage is 20 m. With the advancement of the in-seam seismic wave detection technology, it is expected to detect a smaller scale collapse column structure under appropriate detection conditions.
Q2: Can in seam seismic exploration technology be sufficient to judge the water content of faults and collapse columns?
A: In-seam seismic exploration technology uses the propagation characteristics of mechanical waves (elastic waves) to detect structural anomalies, and cannot directly determine the water-bearing characteristics of the structures.
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