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In order to ensure the dehydration effect of the whole tailings backfill, a dehydration model of the whole tailings backfill was established based on hydrodynamics on the basis of satisfying certain assumptions, and the theoretical solution was carried out. The control variable method is used to study the variation of dewatering capacity with dewatering depth and radius, and the applicability of the dewatering model is verified by experiments. The results show that the dewatering capacity increases with the increase of dewatering radius and decreases with the increase of dewatering depth by a quadratic polynomial. By comparing the experimental values with the theoretical ones, it is found that the variation law of the dewatering capacity with radius is the same and increases with the increase of dewatering depth. The reason is that the content of fine particles in the unclassified tailings is large and the filter hole on the branch pipe is blocked under the action of the hydrodynamic force. Therefore, the dewatering effect of the new root-like dehydration tube can be guaranteed by using the branch pipe arranged at the full height of main dewatering pipe. The dehydration model is modified by the test results to ensure the applicability.

A safe, efficient, and low-cost dewatering technology is essential to ensure the filling effect. Under the current mining situation, if cemented filling is used in the large goaf formed in the mining process of low-grade deposits, the stability of the filling stope can be guaranteed, but the filling cost is high. If cementless filling is used, the dewatering effect cannot be guaranteed and the stability of the filling stope cannot be assured, leaving a serious potential safety hazard for mining [

Experts and scholars all over the world have conducted a lot of research on the dewatering technology of fine tailings (see Table

Summary of research achievements in dewatering technology of whole tailings.

Type | Method | Pros and cons |
---|---|---|

External effect | Electro-osmosis [ | The above dehydration method has good dehydration effect, but the cost is high, the related supporting technology is complex, and there are potential safety hazards |

Negative pressure method [ | ||

Forced air method [ | ||

Chain dewatering method [ | ||

No external effect | Setting dewatering closed wall and dewatering well [ | This can improve the dehydration speed to a certain extent, but also lead to the increase of dehydration cost |

Increasing the spacing and diameter of dewatering pipe [ | ||

Adding a certain amount of coarse particles to improve the particle size distribution [ |

Zhang et al. [

Therefore, on the basis of the existing research results, the authors construct the dewatering model of full tailings filling slurry based on hydrodynamics, analyze the variation law of the dewatering amount of full tailings filling slurry with the dewatering depth and dewatering radius, carry out the indoor dewatering test combined with the engineering example, compare the experimental value with the theoretical value, and verify the reliability of the dewatering model of full tailings filling slurry. The research results enrich the dewatering theory of noncemented filling slurry, so as to achieve the purpose of rapid dewatering of filling stope, shorten the filling period, and improve the dewatering effect of filling stope.

Assuming that the slurry is homogeneous and its concentration remains constant during dewatering, the unsaturated hydraulic conductivity of the slurry is constant.

Assuming that the dewatering pipe is evenly distributed in its depth range, the water in the filling body flows to the dewatering pipe along different paths. The closer the dewatering pipe, the more obvious the streamline bending and the greater the hydraulic gradient. With the distance from the dewatering pipe, the streamline bending degree gradually decreases, as shown in Figure

On the right side of Figure

Schematic diagram of water flow in total tailing filling slurry.

In order to facilitate the theoretical calculation, it is assumed that the dehydration model of full tailings filling slurry is shown in Figure

Schematic diagram of the dehydration model of total tailings filling slurry.

According to Darcy’s law and Dupuit assumption, the flux of any infinitesimal element is as follows:

The research method of reference [

According to the axisymmetric condition and potential function, the transformation is carried out:

Assuming that the tailings filling slurry is homogeneous, the following formula holds:

Let

The boundary conditions are as follows:

In formula (

By subtracting formulas (

By substituting the potential function into formula (

According to formula (

Two dehydration pipes are taken as an example to illustrate that, referring to the research method of single dehydration pipe, when two dehydration pipes are near, the dehydration potential of full tailings filling can be calculated according to the superposition principle, which is the following formula:

In the formula, _{1} and _{2} are the dehydration amount of the whole tailings filling slurry corresponding to the two dehydration pipes, _{1} and _{2} are the dehydration radius corresponding to the two dehydration pipes, and _{1} and _{2} are constants.

Generally, the same type of dehydration pipe is used in the project, so the dehydration radius of the two dehydration pipes is the same, that is, _{1} = _{2}. Assuming that the dehydration amount of the whole tailings filling slurry corresponding to the two dehydration pipes is the same, that is, _{1} = _{2}, formula (

Substituting formula (

By substituting the potential function into formula (

The above research shows that dehydration radius

The unsaturated hydraulic conductivity

Variation of dehydration amount with dehydration radius.

It can be seen from the observation of Figure

The dehydration radius is proposed as 4 cm, and the dehydration depth is 4 cm, 8 cm, 12 cm, and 16 cm, respectively. The above parameters are substituted into formula (

Variation of dehydration amount with dehydration depth.

It can be seen from Figure

In conclusion, the effective way to improve the dehydration effect of tailings filling slurry is to lay the branch pipe at the bottom of the main dehydration pipe and increase the length of the branch pipe as much as possible.

In order to verify the reliability of the dehydration model of full tailings filling slurry, the dehydration test scheme of full tailings filling slurry is designed as shown in Table

Test plan of total tailings filling slurry dehydration.

Test group no. | Dehydration depth | Dehydration radius |
---|---|---|

Test group 1 | 16 | 4 |

16 | 5 | |

16 | 6 | |

16 | 7 | |

Test group 2 | 4 | 4 |

8 | 4 | |

12 | 4 | |

16 | 4 |

The experimental results are compared with the theoretical calculation results, as shown in Figures

Comparison of the experimental values of the experimental group with the theoretical values.

Comparison of the experimental values of the two groups with the theoretical values.

It can be seen from Figure

It can be seen from Figure

At the end of the test, a new root-shaped dehydration pipe with a dehydration depth of 4 cm was taken out from the tailings filling slurry. It was found that a tightly wrapped mud layer with a thickness of about 2 mm was formed on the surface of the main dehydration pipe and the branch pipe. All the drainage holes on the main dehydration pipe and the branch pipe had been blocked by tailings particles. Although the dehydration amount was large in the early stage of the test, it could not be dehydrated in the later stage. The new root-shaped dehydration pipe is taken out from the tailings filling slurry, as shown in Figure

A new type of root-like dehydration tube used after the dehydration test.

In order to make the theoretical formula in this paper accord with the actual dehydration situation of tailings filling slurry, formula (

To sum up, the research shows that the change rule of dehydration radius of tailings filling slurry is consistent with that of theoretical value, while the change rule of dehydration depth is different from that of theoretical value. This is because the content of fine particles in tailings is high, the filter holes on the main dehydration pipe and branch pipe are blocked under hydrodynamic effect, and the thickness of 2 mm is formed on the surface of main dehydration pipe and branch pipe, the mud layer of the earth. Therefore, the theoretical formula is modified according to the test results to ensure the reliability of the theoretical model.

In practical engineering, because of the influence of pipe washing water and on-site filling process, it is difficult to ensure that the concentration of full tailings filling slurry does not change after it is filled into the filling stope. Therefore, the unsaturated water conductivity

The process related to the backfilling of cementing filling body dehydration is to install new type root dehydration tube first and then fill the backfilling materials. Although the branch pipes are evenly distributed on the main dewatering pipe, it is difficult to guarantee during the filling process, and it will also affect the dehydration effect of the new root-like dehydration pipe. Therefore, we still need the new root-shaped dehydration branch pipe in the pipe material to carry out the relevant research.

Under the premise of meeting certain assumptions, the dehydration model of full tailings filling slurry is established based on hydrodynamics, and the dehydration radius and depth are determined to be the two main factors affecting the dehydration effect of full tailings filling slurry. The results show that the dehydration capacity of tailings slurry increases with the increase of dehydration radius and decreases with the increase of dehydration depth.

The results show that the variation law of the dehydration radius of the whole tailings filling slurry is consistent with the theoretical value, while the variation law of the dehydration depth is different from the theoretical value. It is found that there is a mud layer on the surface of the main dehydration pipe and branch pipe within a certain depth range of the bottom of the new root-shaped dehydration pipe, which is due to the high content of fine particles in the whole tailings and the low hydrodynamic pressure. Therefore, based on the test results, the theoretical model is modified to ensure the reliability.

The dehydration model of full tailings filling slurry established in this paper does not consider the influence of pipe washing water, on-site filling process, and filling process, so there is a certain gap with the engineering practice. Further monitoring the unsaturated hydraulic conductivity of full tailings filling slurry and seeking new branch pipe materials are the key to ensure the dehydration effect of full tailings filling slurry.

The experimental results used to support the findings of this study are included within the article.

The authors declare that they have no conflicts of interest.

The authors are grateful for the Doctoral Research Start-Up Fund Project of North China Institute of Aerospace Industry (BKY-2020-24) and National Natural Science Foundation of China (51674012).