The overlying strata is often destroyed in large-scale during shallow coal seam mining, and the sliding instability of the caved roof seriously threatens the safety of the mining field. Based on the monitoring data of the roof weighting of a typical shallow coal mining, the load distribution characteristics of the roof along the strike and trend of the mining field were analyzed, and the mechanical model of the pressure-arch in the surrounding rock was established. Then the evolution characteristics of the pressure-arch and the elastic energy of the surrounding rock were revealed during shallow coal mining by theoretical analysis and numerical simulation. The results show that the continuous pressure-arch was formed when the horizontal stress exceeded the primary vertical stress of the mining field, and the elastic energy of the roof was released by the mining unloading effect. The caved zone of the overlying strata was formed below the inner boundary of the pressure-arch. The elastic energy was accumulated in the pressure-arch and the energy arrived the highest at the front arch foot. The accumulated energy at the arch foot was released by coal mining and the shear zone could be formed. So the sliding of the caved zone along the shear zone would induce the strong roof weighting. The concentrated stress and the released energy during each mining increased with the panel advancing, and the height of the shear zone also increased. The conclusions obtained in the study are of important theoretical value to direct the similar engineering practice.
The instability of overlying strata during shallow coal mining, such as the large-scale roof falling and step-like ground subsidence, is a key problem that can restrict the safety mining in the mines (Ju & Xu 2015). The self-bearing structure of the pressure-arch can form in the overlying strata after the coal mining, and this structure can support the load of the upper strata and soil layer, so the weighting intensity of the panel is determined by the caved rock in the unloading zone under the inner boundary of the pressure-arch. A large amount of elastic energy is accumulated in the pressure-arch under the concentrated stress, and the released energy for mining is the internal cause of rock failure (Wang et al. 2017). It is an important problem to reveal the distribution characteristics of the stress and energy fields in the mining field, and to analyze the stability of the overlying strata during shallow coal mining based on the evolution characteristics of the pressure-arch.