Jianguo Ning

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.

Research on the Energy Criterion for Rockbursts Induced by Broken Hard and Thick Rock Strata and Its Application

In this study, the occurrence conditions of rockbursts induced by broken hard and thick rock strata (HTRS) in fully mechanized longwall face are investigated by dividing the surrounding rock of a roadway rib into three zones: burst-resistance zone (BRZ), burst-inoculation zone, and stable zone. On this basis, the process of impact vibration energy (released by the broken HTRS) transformation in these zones was analyzed, and theoretical equations are presented to calculate the strain energy, dissipated energy and shock vibration energy. In addition, an energy criterion associated with the critical broken length of the HTRS, the width of burst-resistance zone, and the burst proneness index was proposed to predict rockbursts induced by broken HTRS in fully mechanized longwall face. Moreover, to control these types of rockbursts effectively, a quantitative method was proposed for determining the limit broken length of the HTRS and the BRZ. The research results show that the energy criterion may forecast these typical rockbursts, and rockburst hazards can be eliminated using the proposed method.

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.

Multiparameter Monitoring and Prevention of Fault-Slip Rock Burst

Fault-slip rock burst is one type of the tectonic rock burst during mining. A detailed understanding of the precursory information of fault-slip rock burst and implementation of monitoring and early warning systems, as well as pressure relief measures, are essential to safety production in deep mines. This paper first establishes a mechanical model of stick-slip instability in fault-slip rock bursts and then reveals the failure characteristics of the instability. Then, change rule of mining-induced stress and microseismic signals before the occurrence of fault-slip rock burst are proposed, and multiparameter integrated early warning methods including mining-induced stress and energy are established. Finally, pressure relief methods targeting large-diameter boreholes and coal seam infusion are presented in accordance with the occurrence mechanism of fault-slip rock burst. The research results have been successfully applied in working faces 2310 of the Suncun Coal Mine, and the safety of the mine has been enhanced. These research results improve the theory of fault-slip rock burst mechanisms and provide the basis for prediction and forecasting, as well as pressure relief, of fault-slip rock bursts.