Yunliang Tan

In Situ Investigations on Failure Evolution of Overlying Strata Induced by Mining Multiple Coal Seams

Accurate evaluation of the failure evolution of the overlying strata after multiple mining actions is of great importance both for the prevention of water disasters and the mining designs. To ensure the safety of mining multiple coal seams, the fracture criterions of overlying strata after mining actions were established on the basis of beam theory as well as the influences of coal seam spacing, face size, and lithology on the increased heights of failure zones after each consecutive mining sequence. A newly developed device, named electric controlled water flow detector, and its detecting procedure, was introduced. In situ investigations were performed in the Gaojialiang and Jinhuagong Mines, China. Results showed that the mining of a lower coal seam does not change the failure evolution of the roof strata of the upper coal seam when the coal seam spacing is large. The larger the mining height of the lower coal seam is, the more fractures the overlying strata of the upper coal seam have, and the larger the height of the failure zone. In addition, the failure extent of overlying strata caused by coal face mining increased with their hardness. It was found that the electric controlled water flow detector can effectively detect the failure evolution during multiple mining actions, with high water plugging effectiveness and detection accuracy.

Dissipation of Impact Stress Waves within the Artificial Blasting Damage Zone in the Surrounding Rocks of Deep Roadway

Artificial explosions are commonly used to prevent rockburst in deep roadways. However, the dissipation of the impact stress wave within the artificial blasting damage zone (ABDZ) of the rocks surrounding a deep roadway has not yet been clarified. The surrounding rocks were divided into the elastic zone, blasting damage zone, plastic zone, and anchorage zone in this research. Meanwhile, the ABDZ was divided into the pulverizing area, fractured area, and cracked area from the inside out. Besides, the model of the normal incidence of the impact stress waves in the ABDZ was established; the attenuation coefficient of the amplitude of the impact stress waves was obtained after it passed through the intact rock mass, and ABDZ, to the anchorage zone. In addition, a numerical simulation was used to study the dynamic response of the vertical stress and impact-induced vibration energy in the surrounding rocks. By doing so, the dissipation of the impact stress waves within the ABDZ of the surrounding rocks was revealed. As demonstrated in the field application, the establishment of the ABDZ in the surrounding rocks reduced the effect of the impact-induced vibration energy on the anchorage support system of the roadway.