The height of fractured water-conducting zone in undermined rock strata

The height of fractured water conducting zone is of significant importance for the safety of underground mining. Because of the conspicuous discrepancy of the height of fractured water conducting zone in Bulianta Coal Mine as predicted by the traditional method with those observed in practice, a systematic research has been carried out. The study indicates that two aspects should be taken into account. Firstly, the traditionally proposed empirical formula in prediction of the height of fractured zone was based on the conditions of single-slice mining where the mining height was less than 3 m and the total slice mining height was limited within 15 m. In such a case, it would not be suitable to predict the maximum fractured zone height for the conditions where a single mining height is larger than 3 m. Secondly, the stratum structure such as the thick and strong rock layer termed as key stratum plays an important role in controlling of the height of movement in the overburden. Physical model tests by making use of a similar material illustrate that if the vertical distance from the primary key stratum to the coal seam is shorter than a certain value, then the developing fracture zone will extend above the key stratum into the top of bedrock, resulting in a larger height of water conducting zone than is calculated by the empirical method. The outcome of the work presented will be helpful in practice to prevent the overburden aquifer inrush and to avoid mine water hazard.

► There are some limitations for the application of the empirical formula (1).
► The key strata has a great impact on the height of movement in the overburden.
► The breakage of key stratum may enlarge the height of the fractured zone.