# Study on Fluid–Solid Characteristics of Grouting Filling Similar-Simulation Materials

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{1}and the permeability similarity coefficient of bed separation grouting simulation Π

_{2}are deduced. When models are built with different geometric dimensions, these coefficients can be used to efficiently adjust the experimental parameters by judging whether the time and permeability meet the requirements.

## 2. Experimental Program

#### 2.1. Deduction of the Similarity of Fluid-Solid Materials

_{1}and F

_{2}are identical. Thus,

_{a}. Therefore, the function can be expressed as follows:

_{1}, Π

_{2}, and Π

_{3}can be obtained as follows:

_{1}, Π

_{2}, and Π

_{3}, and the similarity ratio to be determined is C

_{γ}, C

_{t}, and C

_{l}. The similarity assumption is made for the similar-simulation material in this experiment and the similarity constant is determined as C

_{L}= 0.0025. Then, the stress similarity ratio is obtained as C

_{σ}= 0.0018 and the bulk density similarity ratio is obtained as C

_{γ}= 0.72. After simplification, it can be obtained that Π

_{1}= gt

^{2}/l, Π

_{2}= gt

^{2}/l, and Π

_{3}= k/l

^{2}, therefore Π

_{1}= Π

_{2}. The solution of the similarity criterion must be determined in combination with subsequent experiments. The calculated similarity criterion can be used to quickly determine whether the similarity degree of the material meets the requirements and the water-physical properties of similar materials can be adjusted according to the similarity criterion. Since Π

_{1}is mainly determined by geometric similarity ratio C

_{l}and time similarity ratio C

_{t}, then Π

_{1}is defined as the simulation time similarity coefficient of bed separation grouting. Π

_{3}is mainly determined by geometric similarity ratio C

_{l}and permeability similarity ratio C

_{k}. Therefore, Π

_{3}is defined as the permeability similarity coefficient of the bed separation grouting simulation. According to the compressive strength of the original rock, the expected strength of the similar-simulation material can be determined. Based on the control variable method, similarity constant, and strength similarity ratio, the physical and mechanical parameters of the model are measured to verify the similarity of the similar-simulation material.

#### 2.2. Determination of Preparation Parameters

#### 2.3. Physical and Mechanical Tests

- For the hard rock group (H group), the compressive strength of rock specimens prepared in different batches is different; the maximum compressive strength is 154 KPa, the minimum compressive strength is 129 KPa, and the average compressive strength is 144 KPa, with a deviation of 10.2. The strength deviation of rock specimens in the H1-3 group is relatively large.
- For the medium-hard rock group (M group), the maximum compressive strength of rock specimens is 137 KPa, the minimum compressive strength is 115 KPa, the average compressive strength is 126 KPa, the deviation is 6.6, and the overall data are credible.
- For the soft rock group (S group), the maximum compressive strength of rock specimens is 89 KPa, the minimum compressive strength is 64 KPa, and the average compressive strength is 80 KPa, with a deviation of 11.1. The deviation of rock specimens in the S1-3 group is relatively large.

## 3. Hydrological Experiments

#### 3.1. Water Immersion Experiment

#### 3.2. Water Storage Experiment

- There is a linear relationship between the time and the water absorption rate of rock specimens in different groups, and the saturation no longer increases after 72 h. The average saturated water storage rate of rock specimens with straw powder is 9.6% and that of rock specimens without straw powder is 3%. Therefore, the straw powder can improve the water storage rate of rock specimens by more than 300%.
- The average water storage rate of rock specimens with straw powder is 2% within 24 h and that of rock specimens without straw powder is less than 1%. After 48 h, the average water storage rate of rock specimens with straw powder is more than 4.5%, while that of rock specimens without straw powder is less than 2%. It can be seen that the water absorption rate of rock specimens with straw powder is relatively slow at the first 24 h and then the water absorption rate significantly increases. This is because the oil film inside the material hinders the formation of the water absorption pathway. However, with the increased time, the oil film continues to seep out and form a pore channel inside the sample. Therefore, the water absorption rate slowly increases first and then increases rapidly.

#### 3.3. Permeation Experiments

- The permeability difference of rock groups with different lithologies is small and the greater the hardness of rock specimens, the worse the permeability.
- The average permeability of the rock group without PVA is 1.45 × 10
^{−6}cm/s, while the average permeability of the rock group with PVA can reach 2.36 × 10^{−5}cm/s. Therefore, PVA material significantly improves the permeability of rock materials and the permeability improvement rate reaches 1627%.

## 4. Application

## 5. Conclusions

- (1)
- According to the above experimental results, the similarity coefficients of the time similarity ratio, geometric similarity ratio, and permeability similarity ratio are obtained as follows: Π
_{1}= Π_{2}= gt^{2}/l = 0.025 and Π_{3}= k/l^{2}= 1,600,000. Additionally, Π_{1}and Π_{2}are defined as the time similarity coefficients of the bed separation grouting simulation and Π_{3}as the permeability similarity coefficient of the bed separation grouting simulation.These coefficients provide a reference for research and development of similar-simulation materials for the bed separation grouting simulation. According to the experimental needs, these coefficients can be used to adjust the geometric similarity ratio, time similarity ratio, and permeability similarity ratio. - (2)
- A similar-simulation material with the adjustable strength of 80 KPa–144 KPa was obtained under limited experimental conditions. The experimental results verify that this material does not disintegrate in water and its water storage rate can be adjusted between 3% and 9.6%, and the permeability can reach 2.36 × 10
^{−5}cm/s. - (3)
- The similar-simulation experiment of mining-induced bed separation grouting was carried out in a three-dimensional physical experiment system at a similarity ratio of 1:400. The results show that the permeability of the similar-simulation material is strengthened by the generated cracks via the rock strata migration undermining and the volume of the bed separation is smaller than that of the grouting in the grouting process. This indicates that the material can successfully simulate the water loss and consolidation process of slurry and be used for grouting simulation experiments.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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Simulated Lithology | Paraffin | Lubricating Oil | Talc Powder | Sand | Straw Powder | PVA |
---|---|---|---|---|---|---|

Hard rock | 4.5 | 4.5 | 9 | 80 | 2 | 2 |

Medium-hard rock | 3 | 4.5 | 10.5 | 80 | 2 | 2 |

Soft rock | 2 | 4.5 | 11.5 | 80 | 2 | 2 |

**Note:**PVA disappeared after dissolving in water, thus it was not involved in the total mass ratio.

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**MDPI and ACS Style**

Zheng, K.; Xuan, D.; Li, J. Study on Fluid–Solid Characteristics of Grouting Filling Similar-Simulation Materials. *Minerals* **2022**, *12*, 502.
https://doi.org/10.3390/min12050502

**AMA Style**

Zheng K, Xuan D, Li J. Study on Fluid–Solid Characteristics of Grouting Filling Similar-Simulation Materials. *Minerals*. 2022; 12(5):502.
https://doi.org/10.3390/min12050502

**Chicago/Turabian Style**

Zheng, Kaidan, Dayang Xuan, and Jian Li. 2022. "Study on Fluid–Solid Characteristics of Grouting Filling Similar-Simulation Materials" *Minerals* 12, no. 5: 502.
https://doi.org/10.3390/min12050502