1. Introduction
In the process of roadway excavation, encountering hidden geological anomalies that have not been detected in advance will seriously affect the smooth layout of the production system, design and excavation work. The resulted unusable roadways and the tardiness will cause significant economics loss to coal mine safety and efficient production. Therefore, the timely and accurate detection of the hidden geological anomalies in front of the excavation, especially the geological structure, is of great significance for rational design, adjustment of the mining layout, and ensuring safe and efficient production.
2. Treatment solution
The self-innovated seismic advance detection technology for roadway heading is a special reflection method for detection of geological anomalies that may exist in front of the roadway face. Shot points and geophones were deployed on both sides of the blind alley. Geological anomalies within certain distance in front of the roadway excavation face could be detected and predicted through analysis of the characteristics of seismic wave record received by geophones. The detection distance could reach 200m.
Figure 1 Schematic diagram of deep hole detection and observation
Figure 2 Schematic diagram of the multi-channel passive geophones in a horizontal hole
Figure 3 Multi-channel geophones for the horizontal holes
3. Work situation
Borehole-roadway combined advance exploration system is shown in Fig 4. Geophones were deployed near the roadway end. 22 sets of shallow-hole three-component geophones were arranged on one side. Distance between adjacent geophones was 10m. X is the direction along the tunnel, Y is perpendicular to the tunnel wall, and Z is the vertical direction; 3 geophones were arranged in 60 m deep boreholes. Diameter of the boreholes was 70 ~ 100 mm, the boreholes were 45 m away from the roadway head. The first shot occurred at 40 meters away from the roadway head, on the same side of the geophone. Totally 21 shots were conducted.
Figure 4 Advanced observation system in roadway
4. Achieved accomplishment
The effective channel wave frequency band of this data was obtained by frequency sweep, and the imaging analysis was carried out based on this. In the imaging profile, the blue (cold color) area had weak energy and belonged to the normal area, while the red (warm color) area had strong energy and was the abnormal area. Under normal circumstances, when there were faults, collapse columns and other geological anomalies around the roadway, the anomalous body was used as a diffractive point to generate the diffracted waves, and the resulted diffraction imaging of the diffracted wave reflected the location of the anomalous body. The warm color anomalies on the upper and the lower sides of the roadway in the picture were the reflection of the faults around the roadway. According to the results of the channel wave energy imaging, the working face was explained, and the following comprehensive geological results were obtained from the comprehensive analysis: (1) Anomaly 1 was located in the lower roadway At 210 m head-to-head, the lateral span was about 110 m and the longitudinal span was about 55 m. It was inferred to be a fault that intersected the roadway at an angle of 45-degree. (2) Anomaly 2 was located at 76 m in front of the upper lane and was an anomalous diffractive body. At present, these two faults have been verified, which is highly consistent with the actual exposed position.
Fig. 5 Detection results of the channel waves
5. FAQ
Q1:What geological problems can the advanced channel wave detection in the front of a roadway resolve？
A：At present, it can detect the abnormal geological bodies of certain size within 200 m head-on in the head-on front, such as the goab, fractured zone of fault, washout zone, water-bearing body, collapse column, gas-accumulating zone.
Q2：How many channel wave seismic exploration projects have you accomplished so far？What is the application effect？
A：Using the successfully developed geophones and the predetermined related operation methods, we have successively accomplished the industrial test in Yushupo Mine, Wangjialing Mine, Jianzhaung Mine, Yangquan No.1 and No.2 mines, and carried out the related data processing and interpretation. In consideration of the factors such as the working efficiency and the data quality, we have adopted the working mode of the excitation and the reception in roadways, conducted the advanced detection in more than 10 mines, gotten good application effect , received the favourable reviews from the mines.
Q3：What environmental requirements does this method have？
A：It is suitable for all excavation roadway, but the roadway must be a coal roadway, For the geophones in the holes, the water detection and drainage holes as well as the gas drainage holes are required nearby the face, the depth of the holes must be 60 m and the diameter over 75 mm.
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