In order to explore the pressure relief and structure stability mechanism of lateral cantilever structure in the stope under the direct coverage of thick hard roof and its impact on the gob-side entry retaining, a lateral cantilever fractured structural mechanical model was established on the basis of clarification for the stress environment of gob-side entry retaining, and the equation of roof given deformation and the balance judgment for fracture block were obtained. The optimal cantilever length was proposed based on the comparison of roof structural characteristics and the stress, deformation law of surrounding rocks under six different cantilever lengths by numerical simulation method. Double stress peaks exist on the sides of gob-side entry retaining and the entry located in the low stress area. The pressure of gob-side entry retaining can be relieved by reducing the cantilever length. However, due to the impact of arch structure of rock beam, unduly short cantilever would result in insufficient pressure relief and unduly long cantilever would bring larger roof stress which results in intense deformation. Therefore, there is optimal cantilever length, which was 7−8 m in this project that enables to achieve the minimum deformation and the most stabilized rock structure of entry retaining. An engineering case of gob-side entry retaining with the direct coverage of 10 m thick hard limestone roof was put forward, and the measured data verified the reasonability of conclusion.

Due to natural environmental conditions and the effect of man, geological disasters (landslides, earthquakes, etc.) pose a serious threat to ancient relics distributed across China. In consideration of the current situation at the Tonglushan ancient copper mine relics, and on the basis of hydrology and geological engineering conditions of ancient relics, major factors affecting slope stability of ancient relics are analyzed. In light of major working condition types in the slopes of ancient relics, slope stability in relation to earthquakes and rainfall is analyzed using GeoStudio software with limit equilibrium methods. Results indicate that, with sustained rainfall, all slopes in the current reinforcement measure maintain a suitable stabilization status, but slope stability will sharply decline in response to an earthquake. Therefore, the influence of mining blasting activities on slope stability is analyzed. In view of the deformation characteristics of ancient copper mines, the sliding force remote monitoring and warning system based on the constant resistance and large deformation anchor bolt is adopted to continuously monitor the stability of the west slope of the relics. Monitoring results show that the application of ''mechanical gun'' instead of ''explosive blasting'' mining technique in the open-pit mine has effectively reduced the influence of mining disturbance on the stability of the western slope. As slope deformation of the relics can be effectively monitored and controlled, our findings provide a theoretical basis to analyze slope stability in other similar cultural relics.

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China, as the largest coal-producing and -consuming country in the world, is highly dependent on its coal industry, or "Black Gold" industry, for the national energy and economy. The consequent environmental crises, however, have persisted for decades, and the most serious effect is surface subsidence induced by underground mining. Underground coal excavation in China has ignored this problem for thousands of years, even though it causes conspicuous damage to the surface ecosystem and construction projects due to the subsidence of overlying strata. This study recommends paste backfilling to replace the space originally occupied by coal resources to avoid such subsidence and proposes backfilling schemes for two mainstream mining methods used in China's collieries, namely, continuous mining and fully mechanised coal mining. These methodologies have been successfully implemented in some collieries, and the gob area can be backfilled immediately to prevent surface subsidence. To promote an ecological OPEN ACCESSEnergies 2015, 8 3629 ideology when conflict exists between economic profits and environmental protection, experience from developed countries should be considered, support and appropriate legislation from the government are essential, and the perspective of colliery managers should be taken into account, and further in-depth study on strata subsidence and backfilling material must be pursued.