Through investigating cracks, faults, collapse columns, and karst, as well as determining mine recharge water sources, this project has achieved the following research results.
Channel type for the mine water supplied by atmospheric precipitation
Fissure passage
Weathering fissure infiltration channel.
Generally, the burial depths of the weathering zone of surface-exposed rock prior to the start of mining activities in coal mines are 10–30 m17,18, while the depth of local weathering fissure development in some mining areas, such as the Datian coal mine in Panzhou, is 65 m. Notably, weathering fissures contain water, phreatic water is present in the vadose zone, and even confined water is present in the low-lying areas of the mountains. On the other hand, the spring water level may have seasonal changes. After starting mining activity, atmospheric precipitation can supply water to the mine through weathering fractures. For example, the water inflow in the auxiliary shaft adit of the Wufeng coal mine in the Bijie area of Guizhou Province may exceed 13 m3/h in the rainy season, while it is only 3 m3/h in the dry season. Once the weathering zone is directly or indirectly connected to the water-conducting fracture zone, atmospheric precipitation can supply the mine.
Mining-induced fissure infiltration channel.
According to the intensity of mining activities and the thickness of the coal seam, the height of the water-conducting fracture zone after coal mining can differ. When the height of the guiding zone, the weathered fracture zone, or the aquifer reaches the surface, atmospheric precipitation may supply the mine through mining-induced fractures. Figure 3 shows that coal mining may result in a large number of surface fractures, which is conducive to the collection and infiltration of atmospheric precipitation. Due to a large number of coal seam outcrops in Guizhou, inclined shaft development has been adopted in most coal mines. The initial mining areas are typically near shallow outcrops. In the early stage of mining, the water-diverting fracture zone is affected by the supply of atmospheric precipitation. For example, the nearest distance between the 10,501 working face of the Jiaxing coal mine in Nayong County and the surface is 95 m. In this case study, the maximum water inflow during rainy seasons after mining reaches 51 m3/h, while the water inflow during dry seasons decreases to 3 m3/h. Then, it becomes stable at 2 m3/h. As another example, the No. 6 coal seam of the Shengan coal mine in Jinsha County is 162 m away from the nearest surface. In this case study, the maximum water inflow is 69 m3/h in rainy seasons, while it decreases to 5 m3/h in dry seasons.
Water-conducting faults
Fault structures are present in the Guizhou karst area, and the exposed surface faults account for a large proportion of the faults exposed by exploration (see Table 2). Some faults have been activated due to later mining activities26,27, forming water-diversion channels that fill the working face or roadway with atmospheric precipitation through karst aquifers, working face water-diverting fracture zones, surrounding rock fractures, etc. Some faults close to the surface can supply atmospheric precipitation directly to the mining face after the roadway is exposed or the working face is mined. For example, during the rainy season, the 10,403 fully mechanized mining face of the Shiqiao coal mine in Qianxi County is located at the footwall of a reverse fault with a drop greater than 30 m. After the working face is pushed 23 m, the working face produces water, with a maximum water yield of 522 m3/h. The water source is the atmospheric precipitation collected in a low-lying place 2 km away from the working face. Atmospheric precipitation penetrates into the underground working face through a reverse fault, resulting in an accident due to a flooded surface. After several consecutive days of rainfall, the water inflow in the working face rapidly decreases to less than 15 m3/h, and the water inflow in the goaf is 3 m3/h after the working face is mined.
Water diversion collapse column
Sinkholes and underground karst pipelines are relatively developed in karst landforms in Guizhou, and they are good supply channels for atmospheric precipitation28. The development of karst in the Maokou Formation limestone (P2m) in the extremely thick layer at the bottom boundary of the coal measure stratum provides good conditions for the development of the collapse column. When the collapse column develops above the top plate of the coal measure stratum, it is connected with the sinkhole at the surface, giving it the conditions for atmospheric precipitation to replenish the mine. After the collapse column is destroyed by coal mining, an initial small…
Read More: Characteristics of an underground stope channel supplied by atmospheric