# Numerical and Experimental Study on a Novel Filling Support Method for Mining of Closely Spaced Multilayer Orebody

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Bolt-Filling Support Method and System

## 3. Numerical Simulation Study of Bolt-Filling Support

#### 3.1. Calibration of the Microscopic Parameters

^{2}, and ln${(\mathrm{k}}_{\mathrm{n}}/{\mathrm{k}}_{\mathrm{s}}$) (Figure 3). In addition, the uniaxial compressive strength(${\mathsf{\sigma}}_{\mathrm{c}}$) and tensile strength(${\mathsf{\sigma}}_{\mathrm{t}}$) also have a strong correlation with ${\mathsf{\sigma}}_{\mathrm{n}}$, c, μ (Figure 4 and Figure 5). Finally, the equations for the Poisson’s ratio (Equation (1)), elastic modulus (Equation (2)), uniaxial compressive strength (Equation (3)), and tensile strength (Equation (4)) of the rock are fitted.

#### 3.2. Fracture Expansion of Surrounding Rock and Distribution Law of Force Chain

#### 3.2.1. Upper Goaf Not Supported

#### 3.2.2. Upper Goaf 100% Filled

#### 3.2.3. Upper Goaf 95% Filled

#### 3.2.4. Bolt-Filling Support

## 4. Similarity Simulation Experiment of Bolt-Filling Support

#### 4.1. Similarity Experiment Design

#### 4.1.1. Similarity Constants

- (1)
- Geometric Similarity Constant

- (2)
- Bulk Density Similarity Constant

^{3}~1.8 g/cm

^{3}when only river sand is used as aggregate. The actual ore density is around 2.5 g/m

^{3}, so it is more reasonable to set the specific gravity similarity constant as ${\mathrm{C}}_{\mathsf{\rho}}\text{}=\text{}1.5$.

- (3)
- Strength Similarity Constant

- (4)
- Time Similarity Constant

#### 4.1.2. Selection and Preparation of Similarity Experiment Materials

#### 4.1.3. Similarity Model Building

#### 4.2. The Similarity Simulation Experiment Process

#### 4.2.1. Arrangement of Strain Gages

#### 4.2.2. Similarity Experiment 1: Excavation of Double-Layer Ore Body without Support

#### 4.2.3. Similarity Experiment 2: Excavation of Double-Layer Ore Body with Support

#### 4.3. Experiment Results

#### 4.3.1. Results of Experiment 1

^{−4}is in the middle of the stope at monitoring point e3. This phenomenon agrees with the simulation results in Figure 9c, where the force chains are denser in the middle of the roof. The results show that the strain value in the middle of the roof of the stope is larger than the strain values on both sides, and it gradually increases by the influence of mining in adjacent stopes. Similar as E1, the strain of each monitoring point (f1–f5) of the F1 roof (indeed the interlayer between E1 and F1) also increases rapidly after the mining of E1, and fluctuates shortly during the mining of E2, and then increase slowly. After completing the mining of F1, the strain of each point increases sharply again, and the increase fall back again when mining F2. The strains at each monitoring point are f3, f2, f4, f5, and f1 in descending order, and the maximum strain value of 2.52 × 10

^{−4}also appears at monitoring point f3 in the middle of the stope.

#### 4.3.2. Results of Experiment 2

^{−4}and 2.60 × 10

^{−4}, respectively. That is, the deformation of the roof of the upper goaf is greater than that of the floor. During the filling process, the deformation of the roof and floor is slightly reset due to disturbance, while the strain value of the unfilled goaf remains unchanged. After the lower ore body is mined, the strain values of all the monitoring points further increase, and the strain values of points a2, a6 and a10 are still greater than those of points b2, b6 and b10. The support methods influence the final strains obviously if we observe A1 and B1, A2 and B2 and A3 and B3 in pairs. The monitoring points a2 (roof of A1) and b2 (roof of B1 in interlayer) are corresponding to the bolt-filling support, and they have the smallest strains which are 4.03 × 10

^{−4}and 3.02 × 10

^{−4}, respectively. The monitoring points a6 (roof of A2) and b6 (roof of B2 in interlayer) are corresponding to the conventional filling support, and they have the second smallest strains which are 4.61 × 10

^{−4}and 3.31 × 10

^{−4}, respectively. The strains of a10 (roof of A3) and b10 (roof of B3 in interlayer) without support measures are the largest, which are 5.37 × 10

^{−4}and 7.73 × 10

^{−4}, respectively. The smallest deformation proves that the support effect of bolt-filling support is better than that of pure filling support. The experiment results agree with the fracture and force chain analysis in Figure 9,Figure 11, and Figure 12 very well.

## 5. Discussion

## 6. Conclusions

- (1)
- A novel bolt-filling support method is proposed in this research.
- (2)
- It is revealed that, by numerical simulation of fracture distribution and force chains, bolt-filling support not only reduces the roof load of the lower goaf, but also helps to relieve the tensile stress concentration in the roof of the upper goaf caused by incomplete filling, which is effective for the support of closely spaced multilayer goaf.
- (3)
- It is found that, by similarity experiments, the deformation of the roof and interlayer under bolt-filling support is the smallest, which has a high consistency with the numerical simulation results.
- (4)
- Therefore, it is safe to say that the bolt-filling support performs better than other conventional support methods for mining closely spaced multilayer orebodies, so that to promote mining safety and the stability of the roof and interlayer.

## 7. Patents

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Demonstration of the bolt-filling support system. (

**a**) Schematic diagram of bolt-filling support; (

**b**) Longitudinal section of drill hole arrangement for closely spaced multilayer orebodies; (

**c**) Cross-sectional view of drill hole arrangement for closely spaced multilayer orebodies; (

**d**) Longitudinal section of bolt-filling support system for closely spaced multilayer orebodies; (

**e**) Top view of cable bolt network. 1—Surrounding rock, 2—Roof hole, 3—Goaf, 4—Floor hole, 5—Rock bolt, 6—Cable bolt, 7—Pre-loop, 8—Cable bolt network, 9—Backfill, 10—Ore body, 11—Ore pile.

**Figure 2.**Correlation between Poisson’s ratio and stiffness ratio and friction coefficient. (

**a**) Relationship between stiffness ratio ${\mathrm{k}}_{\mathrm{n}}/{\mathrm{k}}_{\mathrm{s}}$ and Poisson’s ratio $\mathsf{\nu}$; (

**b**) Relationship between friction coefficient μ and Poisson’s ratio $\mathsf{\nu}$.

**Figure 3.**Correlation between elastic modulus and effective modulus of contact, friction coefficient, and stiffness ratio. (

**a**) Relationship between effective modulus of contact ${\mathrm{E}}_{\mathrm{c}}$ elastic modulus $\mathrm{E}$; (

**b**) Relationship between square of friction coefficient ${\mathsf{\mu}}^{2}$ and elastic modulus $\mathrm{E}$; (

**c**) Relationship between logarithm of stiffness ratio ${\mathrm{ln}(\mathrm{k}}_{\mathrm{n}}/{\mathrm{k}}_{\mathrm{s}})$ and elastic modulus $\mathrm{E}$.

**Figure 4.**Correlation between uniaxial compressive strength and the tensile strength, cohesion of bonds, and friction coefficient. (

**a**) Relationship between tensile strength ${\text{}\mathsf{\sigma}}_{\mathrm{n}}$ and uniaxial compressive strength ${\mathsf{\sigma}}_{\mathrm{c}}$; (

**b**) Relationship between cohesion of bonds c and uniaxial compressive strength ${\mathsf{\sigma}}_{\mathrm{c}}$; (

**c**) Relationship between friction coefficient μ and uniaxial compressive strength ${\mathsf{\sigma}}_{\mathrm{c}}$.

**Figure 5.**Variation curve of rock’s tensile strength with cohesion and tensile strength of bonds. (

**a**) ${\mathsf{\sigma}}_{\mathrm{t}}$ − c; (

**b**) ${\mathsf{\sigma}}_{\mathrm{t}}$ − ${\mathsf{\sigma}}_{\mathrm{n}}$.

**Figure 6.**Uniaxial compressive experiment of surrounding rock and ore. (

**a**) Uniaxial compression experiment of carbonaceous shale; (

**b**) Uniaxial compression experiment of Vanadium-bearing shale.

**Figure 7.**Stress–strain curve of surrounding rock and ore (1—Simulation curve, 2—Test curve). (

**a**) Surrounding rock; (

**b**) ore.

**Figure 9.**Mechanics simulation of surrounding rock without support. (

**a**) No support in the upper goaf; (

**b**) Distribution of fractures when the upper goaf is not supported; (

**c**) Distribution of the force chains when the upper goaf is not supported.

**Figure 10.**Mechanics simulation of surrounding rock with the upper goaf 100% filled. (

**a**) Filling support in the upper goaf (100%); (

**b**) Distribution of fractures when the upper goaf is 100% filled; (

**c**) Distribution of the force chains when the upper goaf is 100% filled.

**Figure 11.**Mechanics simulation of surrounding rock with the upper goaf 95% filled. (

**a**) Filling support in the upper goaf (95%); (

**b**) Distribution of fractures when the upper goaf is 95% filled; (

**c**) Distribution of the force chains when the upper goaf is 95% filled.

**Figure 12.**Mechanics simulation of surrounding rock with bolt-fill support. (

**a**) Bolt-filling support in the upper goaf; (

**b**) Distribution of fractures with upper bolt-filling support; (

**c**) Distribution of the force chains with upper bolt-filling support.

**Figure 16.**Model building process. (

**a**) Paste the model background image; (

**b**) Mixing materials; (

**c**) Filling materials in layer; (

**d**) Finished model.

**Figure 18.**Sensor Installation. (

**a**) Fixing strain gages; (

**b**) Connecting strain gages to monitoring system.

**Figure 19.**Layout of the stopes and monitoring points for the double-layer ore body mining experiment.

**Figure 20.**Excavation process of experiment 1. (

**a**) Excavation of E1; (

**b**) Excavation of E2; (

**c**) Excavation of F1; (

**d**) Excavation of F2.

**Figure 22.**Mining process of experiment 2. (

**a**) Excavation of A1, A2, A3; (

**b**) Excavation of B1, B2, B3 and support of A1, A2.

**Figure 23.**Picture of bolt-filling support. (

**a**) Similar experimental bolt-filling support diagram; (

**b**) Rock bolt and cable bolt connection diagram.

Rocks | E (GPa) | $\mathsf{\nu}$ | ${\mathsf{\sigma}}_{\mathbf{c}}\text{}\left(\mathbf{Pa}\right)$ | ${\mathsf{\sigma}}_{\mathbf{t}}\text{}\left(\mathbf{MPa}\right)$ |
---|---|---|---|---|

Ore | 1.09 | 0.22 | 1.33 | 0.23 |

Surrounding Rock | 1.48 | 0.20 | 2.35 | 0.30 |

Rocks | ${\mathsf{\sigma}}_{\mathbf{n}}\text{}\left(\mathbf{Mpa}\right)$ | C (Mpa) | Ec (Gpa) | $\mathsf{\mu}$ | ${\mathbf{k}}_{\mathbf{n}}/{\mathbf{k}}_{\mathbf{s}}$ |
---|---|---|---|---|---|

Ore | 0.37 | 0.75 | 0.56 | 0.70 | 1.84 |

Surrounding Rock | 0.56 | 1.13 | 0.75 | 0.30 | 1.39 |

Support Method | Number of Fractures | Fractures on the Roof of Upper Goaf | Tensile Force Chains on the Roof of Upper Goaf | Fractures on the Roof of Lower Goaf | Tensile Force Chains on the Roof of Lower Goaf |
---|---|---|---|---|---|

Unsupported | 1311 | Extremely developed | Dense | Extremely developed | not so dense |

Complete filling (100%) | 379 | Not developed | Sparse | Developed | dense |

Incomplete filling (95%) | 652 | Slightly developed | Not sparse | Developed | dense |

Bolt-filling support | 410 | Not developed | Sparse | Not developed | sparse |

Rock Layer | Density/(kg/m^{3}) | Compressive Strength/MPa | Modulus of Elasticity/GPa | Poisson’s Ratio | Proportion Number |
---|---|---|---|---|---|

Vanadium-bearing shale | 1661.74 | 0.51 | 0.39 | 0.21 | 964 |

Carbonaceous shale | 1620.98 | 0.33 | 0.34 | 0.20 | 1037 |

Siliceous shale | 1704.41 | 0.75 | 0.40 | 0.21 | 837 |

Backfill | 1232.39 | 0.02 | —— | —— | 1019 |

Rock Layer | Volume/m^{3} | Total amount/kg | Cement/kg | Gypsum/kg | River Sand/kg |
---|---|---|---|---|---|

Vanadium-bearing shale | 0.119 | 198.19 | 11.30 | 7.53 | 169.45 |

Carbonaceous shale | 0.588 | 953.10 | 24.69 | 57.62 | 823.13 |

Siliceous shale | 1.237 | 2107.93 | 66.75 | 155.75 | 1780.03 |

Backfill | 0.011 | 13.61 | 0.12 | 1.06 | 11.76 |

Total | 1.955 | 3272.83 | 102.86 | 221.96 | 2784.37 |

Preparation quantity | 2.350 | 3927.40 | 123.43 | 266.35 | 3341.24 |

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## Share and Cite

**MDPI and ACS Style**

Chi, X.; Zhang, Z.; Li, L.; Wang, Q.; Wang, Z.; Dong, H.; Xie, Y. Numerical and Experimental Study on a Novel Filling Support Method for Mining of Closely Spaced Multilayer Orebody. *Minerals* **2022**, *12*, 1523.
https://doi.org/10.3390/min12121523

**AMA Style**

Chi X, Zhang Z, Li L, Wang Q, Wang Z, Dong H, Xie Y. Numerical and Experimental Study on a Novel Filling Support Method for Mining of Closely Spaced Multilayer Orebody. *Minerals*. 2022; 12(12):1523.
https://doi.org/10.3390/min12121523

**Chicago/Turabian Style**

Chi, Xiuwen, Zhuojun Zhang, Lifeng Li, Qizhou Wang, Zongying Wang, Haoran Dong, and Yu Xie. 2022. "Numerical and Experimental Study on a Novel Filling Support Method for Mining of Closely Spaced Multilayer Orebody" *Minerals* 12, no. 12: 1523.
https://doi.org/10.3390/min12121523