# Numerical Analysis of Roadway Rock-Burst Hazard under Superposed Dynamic and Static Loads

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

^{4}J during the mining process are mainly distributed in the hard roof rock layer within 50 m in advance of the working face. The maximum microseismic event energy is 6 × 10

^{7}J. The rock-burst accidents mainly caused by the microseismic event are triggered by the breaking of the hard roof. The vibration wave propagates to the area where the stress is concentrated, causing a sudden release of elastic energy, which causes a rock-burst accident. Even if the panel is relatively shallow and the initial stress is small, because the energy level of the microseismic event is large and the microseismic event occurs very close to the mining working, the potential for a rock-burst due to the strong dynamic load is still high with a low static load.

^{5}–10

^{6}J, and those that occur during mining of the panel are mainly concentrated at 10

^{7}–10

^{8}J. On August 11, 2010, a significant rock-burst accident occurred during the mining of Panel 25110. A total of 362.8 m of the roadway was seriously damaged, and the energy of the burst source was 9 × 10

^{7}J. The damage to the roadway caused by the rock-burst is shown in Figure 1. This rock-burst accident was mainly due to the large, thick and hard rock layer with high strength and good integrity, which is difficult to make fall after the coal seam is recovered. Panel 25110 is deeply buried, and the structural stress in the fault area is high. Mining the panel results in a high stress concentration of the coal mass in front of the working face. The sudden fracturing of the thick and hard roof and fault activation can cause a high-energy seismic event. The superposition of the high static load and the high dynamic load was the main reason for the serious rock-burst accident.

## 2. Model Description

#### 2.1. General Engineering Geology Conditions

#### 2.2. Development of Numerical Models

#### 2.3. Simulation Methodology

^{3}. The horizontal-to-vertical stress ratios σ

_{x}, σ

_{y}are 1.2 and 0.8, respectively, based on a study carried out at a nearby mine.

## 3. Distribution Characteristics of the Deformation and Plastic Zone under Different Loads

#### 3.1. Deformation of the Roadway under Different Superposed Dynamic and Static Loads

#### 3.2. Distribution of the Plastic Zone of the Roadway under Different Superposed Dynamic and Static Loads

## 4. Rock-burst Risk Analysis under Different Superposed Dynamic and Static Loads

#### 4.1. Variation in the Abutment Stress under Different Superposed Dynamic and Static Loads

#### 4.2. Variations in the Peak Abutment Stress and Elastic Energy Density under Different Superposed Dynamic and Static Loads

_{1}, σ

_{2}, and σ

_{3}are the maximum, intermediate, and minimum principal stresses of the unit in the numerical model, respectively, and E and ν are the elastic modulus and Poisson’s ratio of the surrounding rock, respectively.

^{3}to 213.4 kJ/m

^{3}, and the dynamic load provides energy storage for the coal body at the peak abutment stress. When the dynamic load is greater than or equal to 0.6 m/s, the vibration wave is transmitted to the area of the peak abutment stress, causing a significant increase in the stress of the coal body; the greater the PPV is, the greater the magnitude of the stress increase is. After the stress reaches the maximum value, a significant drop occurs, and the higher the PPV is, the faster the decrease is, and the lower the stress after the dynamic load is. When the dynamic load PPVs are 0.6 m/s, 1.0 m/s and 1.4 m/s, the stress values after the dynamic load are 11.0 MPa, 8.02 MPa and 6.77 MPa, respectively, the energy densities are 145.4 kJ/m

^{3}, 56.9 kJ/m

^{3}and 38.6 kJ/m

^{3}, respectively, and the peak stress and elastic energy density are less than those in the static calculation. These results show that the dynamic load causes the coal body to be damaged in the area of the peak abutment stress; that the larger the dynamic load is, the greater the coal body damage is; and that the dynamic load induces a sudden release of elastic energy in the stress concentration area, which can easily cause a rock-burst accident. When the depth of the roadway is 800 m, the peak abutment stress after the static calculation is 35.4 MPa. When the PPV is 0.2 m/s, the peak abutment stress after the dynamic load is 34.9 MPa, which is slightly lower than the abutment stress after the static load. Moreover, Figure 12 shows that the PPV of 0.2 m/s causes a small amount of elastic energy to be released in the roadway at a depth of 800 m. The elastic energy density decreases from 684.9 kJ/m

^{3}to 680.3 kJ/m

^{3}. When the PPVs are 0.6 m/s, 1.0 m/s and 1.4 m/s, the stress values after the dynamic load are reduced to 29.3 MPa, 22.3 MPa and 18.7 MPa, respectively, and the elastic energy density decreases to 597.3 kJ/m

^{3}, 466.5 kJ/m

^{3}and 319.9 kJ/m

^{3}, respectively; the stresses and elastic energy densities are significantly lower than the static calculations. When the PPV is greater than 0.6 m/s, the coal body releases a large amount of elastic energy after the dynamic load. When the roadway depth is 1200 m, the influence of the dynamic load on the peak abutment stress of the roadway is similar to that of the roadway with a depth of 800 m. However, the peak abutment stress and the elastic energy density after the dynamic load are slightly less than with the roadway depth of 800 m. Although the magnitude of the peak abutment stress and the elastic energy density decrease slightly less than with the roadway depth of 800 m, the area where the abutment stress and the elastic energy density are reduced is much larger than with the roadway depth of 800 m. Therefore, the total energy released by the 1200-m-deep roadway after the dynamic load is still greater than that with the 800-m-deep roadway.

## 5. Discussion

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

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**Figure 7.**Deformation of the roadway under different superposed dynamic and static loads. (

**a**) Roof sag under different superposed dynamic and static loads, (

**b**) Ribs convergence under different superposed dynamic and static loads and (

**c**) Floor heave under different superposed dynamic and static loads.

**Figure 8.**Plastic zone of the roadway under different superposed dynamic and static loads. (

**a**) Plastic zone when the roadway is 400 m deep, (

**b**) plastic zone when the roadway is 800 m deep and (

**c**) plastic zone when the roadway is 1200 m deep.

**Figure 10.**Variations of the roadway abutment stress under different superposed dynamic and static loads. (

**a**) Variations of the roadway abutment stress when the roadway depth is 400 m, (

**b**) Variations of the roadway abutment stress when the roadway depth is 800 m and (

**c**) Variations of the roadway abutment stress when the roadway depth is 1200 m.

**Figure 11.**Variations in the elastic energy density in the area of the peak abutment stress under different dynamic and static loading conditions.

Lithology | E_{i} (GPa) | υ | C (MPa) | σ_{t} (MPa) | φ (deg.) | c_{r} (MPa) | ε_{p} (%) |
---|---|---|---|---|---|---|---|

Mudstone | 6.7 | 0.24 | 2.1 | 0.37 | 31 | 0.21 | 0.01 |

Coal | 1.1 | 0.34 | 0.9 | 0.12 | 26 | 0.09 | 0.01 |

Siltstone | 2.9 | 0.28 | 1.2 | 0.2 | 29 | 0.12 | 0.01 |

_{i}is the elastic modulus, υ is Poisson’s ratio, C is the cohesion, σ

_{t}is the tensile strength, φ is the friction angle, c

_{r}is the residual cohesion, ε

_{p}is the plastic parameter at the residual strength.

Type | L (mm) | L_{r} (mm) | D (mm) | F_{t} (kN) |
---|---|---|---|---|

Rebar bolt Cable bolt | 2400 8250 | 1200 2400 | 20 21.6 | 225 510 |

Hazard Level of Roadway | PPV | Depth of Roadway (D) |
---|---|---|

Lack of hazard | PPV ≤ 0.05 m/s | D ≤ 300 m |

Low hazard | 0.05 < PPV ≤ 0.2m/s | 300 < D ≤ 5 00m |

Medium hazard | 0.2 < PPV ≤ 0.4 m/s | 500 < D ≤ 700 m |

High hazard | PPV > 0.4 m/s | D > 700 m |

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**MDPI and ACS Style**

Kong, P.; Jiang, L.; Jiang, J.; Wu, Y.; Chen, L.; Ning, J.
Numerical Analysis of Roadway Rock-Burst Hazard under Superposed Dynamic and Static Loads. *Energies* **2019**, *12*, 3761.
https://doi.org/10.3390/en12193761

**AMA Style**

Kong P, Jiang L, Jiang J, Wu Y, Chen L, Ning J.
Numerical Analysis of Roadway Rock-Burst Hazard under Superposed Dynamic and Static Loads. *Energies*. 2019; 12(19):3761.
https://doi.org/10.3390/en12193761

**Chicago/Turabian Style**

Kong, Peng, Lishuai Jiang, Jinquan Jiang, Yongning Wu, Lianjun Chen, and Jianguo Ning.
2019. "Numerical Analysis of Roadway Rock-Burst Hazard under Superposed Dynamic and Static Loads" *Energies* 12, no. 19: 3761.
https://doi.org/10.3390/en12193761