# Mechanisms and Models of Attenuation of Shock Waves through Rock Formations
## 2 Case Study  
### Geologic Conditions  
The Huijahe Coal Mine is a large underground mine in the northwest of Shaanxi Province. The mining area reaches 52 hectares. Figure 1 shows the location of the coal mine and the layout of the working face. The mine field is located in the middle of the Binchang mining area, with an altitude of about 1200 m. The Binchang mining area is located in the south of the Loess Plateau and the north of the Qinling Mountains. Affected by horizontal stress, there are folds, faults and other special geological structures in the working face. The location of the mine is shown in Figure 1a.  
The coal mine produces 6 million tons of coal annually. Currently, the working faces are 106 and 110 in the 401 mining area. The two working faces are very similar in terms of the layout and distribution of rock formations. The roadway is located in the bottom of the thick coal seam, and the thickness of the coal seam on the roof is 6 to 27 m, with an average of 23 m. A medium sandstone formation of approximately 36 m in thickness is present above the roof. The seismic sources are mainly close to the middle sandstone formation.  
Figure 1b shows the layout of the working face and roadway. The working face is 200 m long with a recovery roadway along its length. The width of the recovery roadway is 5.6 m and the height is 3.7 m. The drainage roadway is on the right with a width of 4.8 m and height of 3.7 m. There is a 30 m coal pillar between the drainage roadway and the recovery roadway. The roof coal of the roadway is very thick. Therefore, the roof is extremely susceptible to collapse in a rock burst.  
According to the mining conditions of the mine, it is a typical mine with high static stress and a thick coal roof. The roof-to-floor and the rib-rib displacement was measured in the mine's recovery roadway. Figure 2 shows the deformation characteristics of the roadway. The roof falling leads to bending of the steel belt, corner failure and floor heaving. Due to the timely cleaning of the roadway floor during recovery, no clear photographs were obtained. It can be seen that the displacement of the roof-floor of the roadway is much greater than that of the rib-rib, and the data collected were used to create a curve of the roadway deformation.  
Figure 1: Mine location and working face layout. (**a**) Location of test site, (**b**) working face layout and cross section of test site.  
Figure 3 shows the deformation curves of the recovery roadway. Large deformations were generated in the area of 100 m distance in front of the coal wall as a result of recovery stresses and dynamic loading. The contraction of the roof-floor reached a maximum of 931 mm and the maximum displacement of the rib-rib was 543 mm, the former being 71.45% greater than the latter. Due to the influence of dynamic loads, the contraction of the roof and floor increases significantly in the range of 40 to 60 m, which shows that the control of the roof and floor of the roadway is the primary safety factor of the roadway.  
Figure 3: Roadway deformation curve.  
Figure 2: Damage characteristics of the roadway: (**a**) roof failure; (**b**) rib and corner damage; (**c**) roadway contour.