Strain energy considerations related to strata failure during caving operations

Mining operations that involve caving of the overlying strata are designed so that caving occurs in a controlled manner by progressive overburden failure. However, there are many cases where the overlying strata bridge over the caved area for longer periods than anticipated and desired. As the caved area expands with the advance of the mining panel, excessive amounts of energy accumulate in the roof strata which will be rapidly released when the overburden eventually fails. The released energy during these failure events consists of the energy released due to the bending failure and other failure mechanisms of the strata, as well as the kinetic energy due to the material movement as it collapses into the gob area. The energy released suffices for triggering small-scale earthquakes which are detectable by local seismographs and can potentially threaten the safety of mine workers as well as damage mine infrastructure. The current work presents and discusses various energy considerations, as well as outlines a number of approaches to estimate the energy factors related to overburden failure in caving operations such as longwall mining. Analytical and numerical methods are examined for their suitability in estimating the elastic energy stored in simplified beam structures overlying gob areas, which could potentially be released in the event of a roof failure. Initial results show that the stored energy increases with beam span but decreases with beam thickness. In addition, the presence of high horizontal has a negligible effect on the stored strain energy.