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Sci Rep
Sci Rep
Scientific Reports
2045-2322
Nature Publishing Group UK London

39261606
72032
10.1038/s41598-024-72032-8
Article
Influence of ore-drawing port position on ore-rock flow characteristics in ore pass and lateral pressure on ore pass wall
Deng Zhe 13
Ma Chi 2
Xia Zhiguo xzgyy88@163.com

1
Ma Qiangying 1
Lu Zengxiang zengxiang_lu@sohu.com

1
1 https://ror.org/03grx7119 grid.453697.a 0000 0001 2254 3960 School of Mining Engineering, University of Science and Technology Liaoning, Anshan, 114051 China
2 https://ror.org/02egmk993 grid.69775.3a 0000 0004 0369 0705 School of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing, 100083 China
3 Minmetals Mining (Handan) Mining Engineering Co., LTD, Handan, 056000 China
11 9 2024
11 9 2024
2024
14 2120215 5 2024
3 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
The blockage and the deformation and failure of the ore pass walls constitute two major problems in applying the ore passes in mines. These problems, which affect the normal operation of mine production, have attracted widespread attention worldwide. The labeled-particle layers method based on numerical simulation was used to investigate the flow characteristics of the ore-rock bulk in the ore pass under different eccentric distances of the ore-drawing port center and ore pass centerline. Moreover, the overpressure coefficient and overpressure number are used to evaluate the degree of damage to the ore-pass wall. The results show that: (1) During the ore drawing process under different eccentricities, the flow patterns of the topmost labeled-particle layers in the ore pass are always in a “—” shaped distribution, and the other layers in the ore pass gradually transition from a “—” shape to a “U” shaped distribution, and then gradually to a “V” shape closer to the drawing funnel; (2) in the range of the ore-drawing funnel, the flow pattern of the ore-rock bulk gradually changes from an upright “V” shape to an italic “V” shape with increasing eccentricity and tip slants to the drawing port, and is less affected in the shaft; and (3) the dynamic lateral pressure caused by the ore-rock flow mainly acts on the lower part of the storage section. When the eccentricity is 0.5 m, the maximum overpressure coefficient and overpressure times are the smallest, leading to the lowest damage degree of the ore pass wall.

Keywords

Ore drawing port
Flow characteristic
Lateral pressure of ore pass wall
Overpressure coefficient
Overpressure number
Subject terms

Civil engineering
Fluid dynamics
the National Natural Science Foundation of China , the Natural Science Foundation of Liaoning Province , and the Outstanding Young Scientific and Technological Talents Project of Liaoning University of Science and Technology.Grant No.51774176, Grant No. 52204137；Grant No. 2022-BS-281；Grant No. 2023YQ10 issue-copyright-statement© Springer Nature Limited 2024
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pmcIntroduction

The Ore pass system, which plays a very important role in ore-rock transportation in underground mining, is a key project for realizing efficient and low-cost downward transport of ore-rock in mines with multi-level development and is widely used in underground mines, especially metal mines, all over the world1–3. However, due to the complex engineering geological environment4,5 and the lousy operating conditions, there are tricky practical considerations in using the ore passes. There are two major problems in the use of the ore pass systems3,6, i.e., the blockage of the ore pass7 and the deformation and failure of the ore-pass wall8, which seriously affect the normal production of the mine.

Many scholars have conducted a large number of studies on the two major problems from different perspectives9–11, e.g., Golshan et al.12 provided a review of the studies of the free-flowing particles flowing inside silos and reviewed and discussed the most significant studies on particles flowing in silos. Esmaieli et al.13 studied the damage range and degree of the main ore pass caused by the layout of the finger raises in the ore pass system in a multi-level production mine. Due to the invisible and unmeasurable characteristics of ore-rock particles moving in the ore pass, DEM has provided a good method for researching bulk material movement in the ore pass. To solve the blockage problem of the ore pass, Hadjigeorgiou and Lessard7 investigated the effect of ore pass geometry, shape, and size distribution of broken ore-rock on material flow in ore pass via the distinct element method. Using discontinuous stress and velocity field methods, Vo et al.14 studied the hang-up in ore passes related to the moisture content and suction of the ore-rock bulk. In addition, Sato and Tang15, by using the 3D-DEM, studied the effect of the cross-section shape of the vertical ore pass on the possibility of the materials hang-up and found that the ore-pass with a square section shape could avoid the hang-up better than that with the circular section shape. Ding et al.16 used an in-house finite element program to predict flow patterns of particulate solids. Wang et al.17 studied the granular flow behavior when discharging from a flat-bottomed geometry of silos, proposed a critical velocity ratio criterion for identifying the flow channel boundary, and found that the flow behavior is closely related to the shear strength of the material. To understand the failure characteristics of the shaft wall in the ore bin during the ore-drawing process, Xia et al.18 carried out an analysis of the flow characteristics, contact compactness, stress distribution characteristics, and contact force probability distribution of the ore-rock bulk by using DEM, and revealed the damage mechanism of the ore pass wall.

The deformation and failure of ore passes, which greatly reduces the efficiency of mine production, are the result of coupling action caused by multiple factors. Among these factors, the movement of ore-rock bulk in the ore pass and its contact with the shaft wall, which leads to a mechanical interaction (such as wear and impact), is the fundamental cause of the deformation and failure of the shaft wall3. According to the mechanical characteristics of the damage to the ore pass wall, it can be divided into impact damage caused by the impacting on the shaft wall by the ore-rock falling in the ore pass and the friction damage caused by the movement of the loose ore-rock bulk in the storage section. Hadjigeorgiou and Lessard studied a major operational issue interrupting the ore-rock flow in ore pass systems in Canadian underground mines19. Based on an investigation in situ, Jiang et al.20 studied the damage of the high-depth inclined ore pass wall, constructed a theoretical model for predicting the damage, and derived the mathematical expression of the total damage volume by using contact mechanics theory.

The factors, such as the drawing funnel's angle and the drawing port’s position, directly affect the macro flow characteristics of ore-rock particles in the ore pass21. Maiti et al.22,23 carried out a comprehensive investigation on the flow behavior of granular material when discharging through an eccentric orifice at the flat bottom in a two-dimensional rectangular silo and found that the eccentricity of the discharging orifice position induces unique complexity in the flow behavior, and extended the kinematic model of granular discharge based on considering the slip flow at the wall.

It is of great significance to study and solve the “two major problems” of ore passes from different perspectives to ensure the reliable discharging of the ore-rock bulk in the ore pass and prolong the service life of the ore pass. This paper, based on the research of many scholars, focuses on the eccentricity of the ore drawing port position and the ore pass centerline, studies the flow characteristics of the ore-rock bulk in the ore storage section when ore drawing at the bottom of the ore pass, investigates the influence mechanism of ore-drawing port position on the mechanical environment of the shaft wall and expects to play a certain role in the solution of the ore pass problem.

Construction of ore-drawing model

Position and eccentricity of ore-drawing port

While ore drawing at the bottom of the ore pass, the ore-rock bulk temporarily stored in the ore storage section (i.e., the ore bin) continuously moves to the drawing funnel and flows out from the drawing port. In the mining engineering of a mine, the center of the drawing port at the bottom of the ore pass does not completely coincide with the ore pass centerline. Taking the difference between the shaft centerline and the center of the drawing port as the connotation, eccentric distance e was introduced to represent the relative position between the drawing port and the ore pass, as shown in Fig. 1.Fig. 1 The Bottom structure of the ore passes under the condition of extreme eccentricity. It consists of the ore storage section and ore drawing funnel. (a) State of center coincidence and (b) State of boundary tangent.

Usually, the cross-section of the ore storage section in the ore pass is a circular shape, and the drawing port is a rectangular shape in situ. Figure 1a shows the coincidence of the centerline of the ore storage section and the center of the drawing port, i.e., the eccentric distance e = 0.0, representing the minimum eccentric distance. Figure 1b shows the boundary of the ore storage section is tangent to one of the boundaries of the ore drawing funnel, and the eccentric distance has a maximum value, i.e., e = (D − d)/2. The other eccentricities between the minimum and maximum values can be calculated via the geometric relationship between the storage section's centerline and the drawing port's center.-

Construction of numerical ore-drawing model

Brief background of the case mine

Shunfeng Iron Mine, a mine with an annual output of 3 million tons of iron ore in Northeast China, is considered the case mine in this research. The orebodies, distributed in parallel in this mine, are a typical sedimentary-metamorphic iron deposit controlled by a north–south fault structure. Affected by different degrees of regional metamorphism and metamorphic iron-silicon construction, the iron deposits and surrounding rocks show layered, quasi-layered, and lenticular-like structures. The ore types of the deposit are hematite quartzite and magnetite quartzite. The surrounding rock of the hanging and foot wall of the orebody is mainly biotite granulite and mixed diagenetic granulite.

The non-pillar sublevel caving mining method is employed to extract iron ore in this mine. The extracted ore is transported from the draw-points by LHDs equipped with a 4m3 bucket to the mine pass, then collected on the haulage level via Granby cars conveyed to the main ore pass adjacent to the skip shaft, and finally lifted to the surface by the skip. Before the ore-rock bulks entered the storage section of the ore pass system, they were crushed into small particles of no more than 300 mm.

According to the structure and the parameters of the ore pass system design in the case mine, the cross-section of the ore pass is a circular shape with a diameter of 6 m and a height of 32 m; the ore drawing port is a rectangular shape with an area of 3 × 2 m2 in situ, and one side of the drawing port is tangent to the wall of the storage section.

Numerical model of ore-drawing

The Distinct-Element Method (DEM) numerical model could properly reflect the properties of granular matter. Therefore, the numerical simulation software used in this paper is Particle Flow Code 2D (PFC2D), the anti-rotation linear contact model and the linear contact model built-in PFC were selected, respectively, for the ore-rock particles and the wall in this paper.

Based on the structure and the parameters of the storage section and the drawing port of the ore pass system design, one of the short sides of the drawing port is 2 m which is tangent to the ore pass wall in situ. According to the definition of eccentricity distance e, it is easy to know that the minimum value of eccentricity e is 0 m, and the maximum value is 1.5 m. That means when e = 0.0 m, the center of the ore drawing port coincides with the centerline of the ore pass. When e = 1.5 m, the wall of the storage section and the short sides of the drawing port are tangent to a certain point. Therefore, in this condition, the eccentricity e changes in the range of [0, 1.5].

Based on the 72° sidewall inclination angle of the ore-drawing funnel when e = 0.0 m, the height of the funnel is calculated to be 4.62 m. According to this height and the height of the storage section, which is 32 m in the case mine, the ore-drawing models (as shown in Fig. 2), which e = 0.0 m (Fig. 2a), 0.5 m (Fig. 2b), 1.0 m (Fig. 2c), and 1.5 m (Fig. 2d), respectively, are constructed based on the ore pass structure as shown in Fig. 1. To analyze the characteristics of the ore-rock particles flowing in the ore pass, the origin of the coordinate of the four ore drawing models is defined to the same point, that is the center of the ore drawing port under the condition of eccentrics e = 0.0 m. The numerical model is shown in Fig. 2.Fig. 2 Numerical ore drawing model of ore pass with different eccentricity e. The height of the ore storage section is 32 m, that of the drawing funnel is 4.62 m, and the minimum inclination angle of the side wall of the ore drawing funnel is 72°, 66.5°, 61.5°, and 56.4°, respectively.

In order to make the numerical simulation better conform to the actual situation of the mine site, the ore-rock particles in the ore pass are collected with a size consistent with the mine site. The size composition of ore-rock particles was determined in the field by screening method, and the result is shown in Table 1.Table 1 Particle size distribution and mass proportion of ore-rock bulks in the mine site.

Particle size (mm)	 < 100	100–150	150–200	200–250	250–300	
Quality Percentage (%)	15	25	30	20	10	

It must be clear that the mesoscopic parameters of the numerical model were gained by the method given in reference 18. The magnetite quartzite, obtained from the mine site, was crushed and screened into different sizes in the laboratory to keep its mechanical properties close to the original ore rock mass. Then, the small-size particles were mixed according to the composition ratio of the block sizes in the mine site to carry out the relevant mechanical tests, and the mesoscopic parameters used for numerical simulation were obtained. Meanwhile, the specific parameters are transcribed in Table 2.Table 2 Mesoscopic parameters of the numerical model18.

Types	Normal stiffness (N/m)	Tangential stiffness (N/m)	Ore-rock bulk density (kg/m3)	Friction coefficient	Anti-rotation friction coefficient	Particle size (m)	Number of particles (N)	
Ore particles	3.33 × 109	3.33 × 109	2050	0.7	0.7	0.1–0.6	13,468	
Wall	3.33 × 109	3.33 × 109	–	0.65	–	–	–	

During the simulation calculation, ore-rock particles with a height of 32 m are generated in the ore pass by the method of falling rain. After the internal force of the ore-rock particles is balanced, a rock particle marker zone with a thickness of 1 m is set every 5 m to observe and analyze the macro flow characteristics of the ore and rock particles. At the beginning of the ore drawing, pressure monitoring points are arranged at intervals of 4 m along the shaft walls on both sides of the ore storage section, and the monitoring points are numbered 1–9 and 10–18 from top to bottom, as shown in Fig. 2a.

Multiple intermittent ore drawing modes were used to study the variation characteristics of ore-rock bulk flow in the ore pass and the drawing funnel and lateral pressure under different eccentricity conditions. The numerical simulation of ore drawing from the constructed model was carried out based on the actual process in the case mine. When the drawn volume of the ore-rock particles for one time reaches 5 m3, the ore drawing will be suspended for a while, and the purpose will be to bring the inner forces in the bulk to a new equilibrium state. Repeat the ore drawing 22 times, and the stored ore-rock bulk material was completely drawn out. Therefore, Fig. 3 shows the flow characteristics of ore-rock bulk ore drawing for 0–20 times.Fig. 3 Variation characteristics of ore-rock bulk particles flowing at different eccentricities e of drawing port and ore-drawing times. (a) Before the ore drawing begining; (b) Ore drawing for five times; (c) Ore drawing for ten times; (d) Ore drawing for 15 times; and (e) Ore drawing for 20 times.

Influence of eccentricity on macroscopic flow characteristics of ore-rock bulk

Flow characteristics of ore-rock bulk

In the process of numerical simulation of ore drawing, the process and state of stored ore-rock particles moving under different eccentricities e were recorded. Figure 3, which shows different eccentricities of the drawing port and the different ore drawing times, shows the macro-flow characteristics of the ore-rock bulk particles in the ore pass.

Taking the minimum eccentricity e = 0.0 m and the maximum eccentricity e = 1.5 m, as examples, the flow characteristics of stored particles in the bottom ore drawn under different eccentricities are compared and analyzed when the ore-rock bulk is dawn at the bottom of the ore pass with different eccentricities e.

Ore-rock flow characteristics with eccentricity e = 0.0 m

When e = 0.0 m, the eccentricity is the smallest, and the center of the ore drawing port coincides with the centerline of the ore pass. Before and after the ore drawing, the flow characteristics of ore and rock particles in the reservoir section are as follows.

Before ore drawing begins, the ore-rock particles do not flow, and the labeled-particle layers are in the shape of a “—”, and are evenly distributed in the ore storage section of the ore pass.

When ore drawing is carried out five times, the labeled-particle layer in the ore drawing funnel presents a “U”-shaped distribution, indicating that within the range of the drawing funnel, the flow of ore-rock particles is differentiated by the particles’ position. The closer to the center line of the funnel, the faster the flow speed of ore-rock particles, while the farther away from the center line, the slower the flow speed. In the range of storage heights from 10 to 24 m, the labeled-particle layers show a “—”-shaped distribution, indicating that the ore-rock particles in the ore pass are in an overall decline, and their flow is not affected by the ore drawing at the bottom of the ore pass. However, in the range of 0–10 m, the labeled-particle layers are in a gradual transition from “—”-shaped to “U”-shaped, indicating that the flow of ore-rock bulk has begun to be affected by the ore drawing, and the flow speed of ore-rock particles near the centerline of the ore pass is gradually accelerated.

After several rounds of ore drawing, the labeled-particle layer located in the drawing funnel shows an obvious "V" shape, while those in the ore storage section show a “U” shape distribution. This indicates that the closer the ore-rock particles are to the centerline and the ore drawing funnel, the faster their flow speed shows a typical "funnel-like flow" characteristic.

Ore-rock flow characteristics with eccentricity e = 1.5 m

When e = 1.5 m, the eccentricity is the largest. The following can be seen from Fig. 3:

Before the ore drawing begins, the labeled-particle layers maintain the same shape as those in the non ore drawing state when e = 0.0 m.

After the ore is drawn five times, the labeled-particle layer, which enters the range of the ore drawing funnel, presents a similar italic “V” shape, and the flow direction of the particles is slanted to the position of the center of the drawing port, and is obviously affected by the position of the drawing port. The labeled-particle layer in the top of the storage section presents a “—”-shaped distribution, the characteristics of those in the range of 0–24 m are in a gradual transition from a “—” to an italic “V”-shaped distribution, and their flow direction constantly deflected towards the center of the ore drawing port.

After several times of ore drawings, the labeled-particle layer in the ore drawing funnel presents an obvious italic “V” shape, indicating that the center of the drawing port has an influence on the direction of the ore-rock bulk flow; the top layer presents a “—”-shaped distribution; the layers in the middle show a gradual transition from “—” to an italic “V” shape, and the flow direction of the particles is obviously affected by the position of the drawing port.

Evolution characteristics of the ore-rock bulk flow rule

To observe and analyze the characteristics of ore-rock particles more clearly and further reveal the macroscopic flow characteristics and the formation mechanism of the flow shape of ore-rock bulk particles under different eccentricities, based on Fig. 3, seven ore-rock particles are extracted from the central horizon of each labelled-particle layer, and their real-time flow position are recorded. The flow characteristics of each labeled-particle layer during ore drawing at the bottom of the ore pass are shown in Fig. 4.Fig. 4 Variation characteristics of 7 extracted ore-rock particles position at different eccentricities e of drawing port and ore-drawing times. (a) Before the ore drawing begining; (b) Ore drawing for five times; (c) Ore drawing for ten times; (d) Ore drawing for 15 times; and (e) Ore drawing for 20 times. I- center line of the ore storage section; II- center line of the drawing port.

Figure 4a shows that the ore-rock flow is not affected by the stored materials before the ore drawing at the bottom of the ore passes. The particles of each labeled-particle layer, which have different eccentricities e, are all distributed as a “—”.

After drawing five times, the particles in the original seventh layer were drawn out from the funnel port, those in the sixth layer completely entered the range of the funnel, and the height of the stored ore-rock bulk decreased. Under the different eccentricities e, it can be seen from Fig. 4b that the distribution of labeling particles in the first layer remains in the “—” distribution shape and those in the second to fifth layers show a transition gradually from a “—” shape to a “U” shape. This phenomenon indicates that the ore-rock bulk moves down in the ore pass as a whole flowing state, there is an obvious vertical displacement difference between the ore-rock particles in the same layer, and the closer to the center line of the ore pass, the greater the displacement of the particles; the closer the ore rock particles are to the drawing port, the more obvious this feature is.

The labeling particles in the 6th layer, which enter the range of the ore drawing funnel, show an obvious “V” type distribution. Moreover, with the increase of eccentricity e, the flow characteristics of ore-rock particles gradually change from a center-symmetric “V” shape to an italic “V” shape. The tip of the italic “V” tends to the center of the drawing port, indicating that the eccentricity e changes the flow direction of the ore-rock bulk in the ore drawing funnel.

After drawing ten times (as shown in Fig. 4c), the labeling particles in the fifth and sixth layers, except a small number of particles in the fifth layer, are drawn out from the drawing port. The labeled particles in the first layer are still distributed as a “—” shape, but those in the second to fourth layers are transformed into a “U” shape. The overall flow of the ore-rock in the ore pass shows a larger displacement difference between the particles near and far away from the center line of the ore pass. Because they are very close to the drawing funnel, the labeling particles in the fourth layer have a “V” shaped distribution.

By comparing the distribution forms of the labeling particles under different eccentricity e, it can be found that with the increase of eccentricity e, the overall flow direction of the labeled particles gradually deflected toward the center of the drawing port from the second layer. Moreover, the greater the eccentricity e is, the closer to the ore drawing funnel. This shows that eccentricity e has an important influence on the evolution of ore-rock flow characteristics. By comparing the information of the first and last five ore drawings, it can also be found that the loss height of the stored ore-rock bulk in the ore pass is different under the condition of the same amount of ore being drawn out. This indicates that the first five ore drawings greatly impact the density of the ore-rock bulk stored in the ore pass.

After drawing 15 times (as shown in Fig. 4d), only the first and second labeled-particle layers remained in the ore pass shaft, and in the range of the drawing funnel, the particles of the third layer and some residue particles of the fourth layer remained. According to the distribution characteristics of the labeling particles in the ore pass, the height of the stored ore-rock in the ore pass decreases significantly. The first labeled-particle layer shows an irregular “—” shape distribution, the second shows an obvious “U” shape, while the third has changed to a “V” shape distribution due to its entry into the drawing funnel.

Comparing the distribution forms of the labeling particles under different eccentricities, it can be found that the ore drawing at the bottom of the ore pass has already affected the distribution characteristics of the first layer. With increasing eccentricity e, the overall flow direction of the labeling particles in the second layer is obviously deflected toward the centerline of the drawing funnel, and the greater the eccentricity e is, the closer the distance from the drawing funnel centerline is. It also shows that the position of the drawing port has an important influence on the evolution of the flow characteristics. According to the analysis of labeling particles residing in the drawing funnel, compared with the position of the residual particles in the 5th layer at the 10th time of ore drawing, the residual labeling particles also occur at the position of the funnel wall, which indicates that the friction between the ore-rock particles and funnel wall greatly slows the flow speed of the ore-rock bulk.

After drawing 20 times, as shown in Fig. 4e, the original first labeled-particle layer in ore pass with different eccentricities is very close to the drawing funnel and shows the distribution characteristics of a “V” shape when e = 0 m, or an italic “V” shape when e ≠ 0 m. Some of the labeling particles in the second layer have been drawn from the drawing port, but the residual particles also show a “V” or italic “V”-shaped distribution. At the same time, a very small amount of the particles in the other layers remain near the funnel wall. This phenomenon shows that the wall angle of the drawing funnel has a great influence on the ore-rock bulk flow in the drawing funnel.

In summary, the change in the eccentricity e of the drawing port, i.e., the variation in the position of the drawing port, has an important influence on the evolution of ore-rock bulk flow characteristics, and the influence is mainly concentrated in the drawing funnel, and the connection between the drawing funnel and the shaft of the ore pass.

Evolution mechanism of the ore-rock bulk flow rule

During the ore drawing process, the movement of ore-rock bulk stored in the ore pass is affected by various forces, such as the gravity of ore and rock particles, the constraining force of the ore pass wall, the friction force between particles and the ore pass wall, etc. all of them affect the movement characteristics of the ore-rock bulk stored in the ore pass to different degrees. The evolution mechanism of ore-rock bulk flow in the ore pass is mainly manifested in the following aspects:

Gravity is the fundamental force for the downward movement and compaction of the ore-rock bulk in the ore pass. Under the action of the gravity of the ore-rock bulk, the contact degree between the particles, between the particles and the shaft wall, is greatly improved, and the strength of the force chains inside the particle is enhanced. The effect of gravity is continuously transmitted to the shaft wall, and the bottom of the ore passes through the force chain, leading to the lateral pressure of the ore pass wall and the vertical pressure to the bottom plate of the ore pass. When the ore is drawn at the bottom of the ore pass, the transmission of this force is a dynamic effect, so the dynamic lateral pressure (DLP) of the shaft wall is formed.

Friction between the ore-rock particles and between the particles and the shaft wall is an important reason for reducing the flow rate of ore-rock particles in the ore pass24. A comprehensive analysis of the friction force between the ore-rock particles and between the particles and the shaft wall reveals that before ore drawing begins, the ore-rock particles, under the condition of internal mechanical equilibrium, do not experience the movement trend of granular materials such as rotation and sliding, and maintain their original spatial shape and arrangement mode. At the beginning of the ore drawing, the spatial form and arrangement of the ore-rock particles are changed under the comprehensive action of various forces. The friction of the shaft wall impedes the movement or rotation of the ore-rock blocks adjacent to the wall, and this part of the ore-rock particle further generates a drag force on the flow of adjacent ore-rock blocks25,26. Due to the effects of the internal friction resistance in the particles and the mechanical transfer loss, the drag force decreases continuously. Finally, the vertical displacement of the ore-rock block increases with increasing drag force transfer distance so that the ore-rock particles near the geometric centerline produce a larger vertical displacement. In comparison, those near the shaft wall produce a smaller vertical displacement. In the end, the flow characteristics of the labeling particles evolved from a “—” shape to a “U” shape and further to a “V”-shaped distribution.

The existence of eccentric distance e between the center of the drawing port and the center line of the ore pass is another main reason for the movement direction deflection of the ore-rock bulk moving near the drawing funnel. The particles’ shape, size, and friction between ore-rock particles and between particles and the ore pass wall will affect the spatial position, arrangement mode, flow speed, and movement direction of ore-rock blocks in the ore pass. However, the key to changingthe “central flow” mode of the bulk is the variation in the “flow center”, and the existence of eccentricity e changes the flow center of the ore-rock bulk.

Influence of eccentricity on lateral pressure of ore pass wall

Variation characteristics of lateral pressure under different eccentricity e

Studying the variation characteristics of the lateral pressure of the ore pass wall is highly important for further studying the wear problem of the ore pass wall. When ore is drawn at the bottom of the ore pass, the relative movement of the stored materials and the shaft wall, the lateral pressure of the ore-rock particles on the ore pass wall, and the friction coefficient between the particles and the shaft wall are the basic conditions and factors that affect the wear degree of the ore pass wall27.

Because the change in eccentricity e directly affects the contact form, spatial distribution, and flow characteristics of the ore-rock particles when ore draws, which further affects the mechanical environment on both sides of the ore pass wall20,28, the study in this section focuses the change characteristics of peak lateral pressure at each measuring point of the ore pass walls based the constructed ore drawing model as shown in Fig. 2. To conveniently analyze the variation characteristics of the lateral pressure of the ore pass wall which are under different eccentricities, the ore pass wall corresponding to the monitoring points 1–9 is called the “left-side wall”, and that to monitoring points 10–18 is called the “right-side wall”. The variation curves of the lateral pressure peak at each measuring point on the left and right-side walls under different ore drawing conditions are shown in Figs. 5, 6, 7 and 8.Fig. 5 Variation characteristics of lateral pressure at each measuring point when eccentric distance e = 0.0 m. Because the difference in lateral pressure on both sides of the shaft is small29, only the left side wall is monitored in real time. (a) Variation of lateral pressure peaks at measuring points 1–4; (b) Variation of lateral pressure peaks at measuring points 5–9.

Fig. 6 Variation characteristics of lateral pressure at each measuring point when eccentric distance e = 0.5 m. (a) Variation of lateral pressure peaks at measuring points 1–4; (b) Variation of lateral pressure peaks at measuring points 5–9; (c) Variation of lateral pressure peaks at measuring points 10–13; (d) Variation of lateral pressure peaks at measuring points 14–18.

Fig. 7 Variation characteristics of lateral pressure at each measuring point when eccentric distance e = 1.0 m. (a) Variation of lateral pressure peaks at measuring points 1–4; (b) Variation of lateral pressure peaks at measuring points 5–9; (c) Variation of lateral pressure peaks at measuring points 10–13; (d) Variation of lateral pressure peaks at measuring points 14–18.

Fig. 8 Variation characteristics of lateral pressure at each measuring point when eccentric distance e = 1.5 m. (a) Variation of lateral pressure peaks at measuring points 1–4; (b) Variation of lateral pressure peaks at measuring points 5–9; (c) Variation of lateral pressure peaks at measuring points 10–13; (d) Variation of lateral pressure peaks at measuring points 14–18.

It can be seen from Figs. 5, 6, 7, and 8 that during the ore drawing process at each eccentric distance model, the DLP of some measuring points increases significantly compared with the static lateral pressure (SLP) when there is no ore drawing, and with the ore-rock particles drawn out from the bottom of the ore pass, the DLP of each measuring point on the shaft wall shows a trend of oscillation up and down, as proven by Wang et al.30. The DLP peak has the largest increase when the measuring point is closer to the ore drawing funnel, such as the pressure peaks at points 1–4 on the left side and at points 10–13 on the right-side wall.

The maximum DLP of the ore pass wall, which can also be clearly observed from the variation curves of the DLP at each measuring point during the ore drawing process, does not occur at the moment when ore drawing begins; it occurs after a period of ore drawing, and it appears at a different ore drawing times.

The variation of the DLP at each measuring point presents the feature of a certain periodicity, and their values do not fully meet the rule of point 1 > point 2 > , …, > point 9. When the maximum DLP appears, it also gradually decreases with the decrease of the height of the storage ore-rock bulk.

Overpressure numbers and coefficient of ore pass wall under different eccentricities

As for the DLP of silo walls, a large number of research results focus on the grain storage31,32. In the process of ore drawing at the bottom of the ore pass, the complex flow characteristics, such as central flow and integral flow, have different influences on the DLP of the shaft wall33, forming the dynamic pressure characteristics of the shaft wall.

When the ore-rock bulk stored in the storage section is in the static state, i.e., there is no ore drawing, and the SLP will be generated on the shaft wall by the stored ore-rock bulk. When ore drawing begins at the bottom of the ore pass, the ore-rock blocks move towards the ore drawing port under the action of gravity, and the DLP which exceeds the SLP will be generated on the shaft wall, resulting in the phenomenon of overpressure34,35.

To further quantitatively analyze the influence of the drawing port position on the DLP of the shaft wall during the ore drawing, the overpressure coefficient (OPC) and overpressure numbers (OPN) accumulated on both sides of the ore pass wall are carried out as the evaluation criteria to semi-quantitative analyze the damage degree of ore pass wall.

When the OPC and OPN were used for evaluating the damage degree of the ore pass wall, it was considered that when the cumulative OPC and OPN are the smallest, the damage degree is the lowest. The evaluation process is as follows:

Firstly, based on the SLP of the ore pass wall, i.e., the pressure when ore is drawn for 0 times, to observe and analyze whether the DLP of each measuring point when the stored ore is drawn under different eccentricity is greater than the SLP. If so, the ratio of DLP to SLP, i.e., OPC is obtained and one time of “overpressure phenomenon” is to be recorded.

Secondly, to add-up the OPN of the left-side and right-side wall respectively. If the accumulative OPN of the left-side wall are greater than that of the right-side wall, it is considered that the ore drawing with an eccentricity e has a greater influence on the lateral pressure of the left-side wall. On the contrary, greater influence on the right-side wall.

Finally, to analyze the OPN and OPC of both sides of the ore pass wall under the same drawing model statistically. It is considered that the damage degree of the ore-rock flow to the ore pass wall will be the lowest when the cumulative value of the OPN and OPC is the smallest. On the contrary, greater damage degree on the ore pass wall.

For the ore drawing model, as shown in Fig. 2, the OPN and OPC of each measuring point when ore drawing with different eccentricities were counted during the simulation, as shown in Table 3.Table 3 Overpressure situation at each monitoring point of ore pass wall under different eccentric distance e.

Position of ore pass wall	Measuring point	Overpressure numbers/times	Maximum overpressure coefficient	
e = 0 m	e = 0.5 m	e = 1.0 m	e = 1.5 m	e = 0 m	e = 0.5 m	e = 1.0 m	e = 1.5 m	
Left-side wall	1	15	3	8	9	6.4	1.56	1.83	2.54	
2	0	1	1	16	0	1.25	1.18	4.83	
3	3	9	2	9	1.42	1.72	1.37	2.62	
4	1	6	0	1	1.07	1.57	0	1.31	
5	1	2	3	0	1.16	1.24	2.09	0	
6	1	0	3	1	1.21	0	1.72	1.09	
7	1	0	1	3	1.06	0	1.15	1.50	
8	0	0	1	3	0	0	1.01	1.21	
9	0	0	0	0	0	0	0	0	
Right-side wall	10	—	2	5	9	—	1.16	1.36	1.78	
11	—	2	0	0	—	1.22	0	0	
12	—	2	11	13	—	1.40	5.21	3.29	
13	—	1	14	0	—	1.09	9.03	0	
14	—	0	4	1	—	0	1.74	1.54	
15	—	0	0	7	—	0	0	3.12	
16	—	0	2	0	—	0	1.15	0	
17	—	0	3	0	—	0	1.46	0	
18	—	0	0	0	—	0	0	0	
“—” represents no this value.

It can be seen from Table 3 that the increase of eccentricity will change the distribution characteristics of OPN and maximum OPC; the point that has the largest OPN is not necessarily the point that has the largest OPC, and the two points at the same height of the both sides wall do not have the same value of OPN and OPC. The distribution characteristics of OPN and OPC under different eccentricity ore drawing ports are analyzed as follows.When e = 0 m, there are six points that occur in different degrees of overpressure phenomenon, where the accumulative OPN is 15 times at point 1, three times at point 3, and one time at rest other. This indicates that the frequency of the overpressure phenomenon occurring in the lower part of the ore storage section is much greater than that in the upper part; for the OPC of each measuring point, the OPC of point 1 is the largest, and point 3 is the next. This indicates that the OPC is positively correlated with the depth of the stored ore-rock bulk.

When e = 0.5 m, there are five points that cause overpressure on both sides of the wall. The OPN of each monitoring point on the left-side wall in size descending order are monitoring points 3, 4, 1, 5, and 2; those on the right-side wall are points 10, 11, 12, and 13, and the OPN of the rest other points is 0. The OPC on the left-side wall in size descending order are points 3, 4, 1, 2, and 5, those on the right-side wall are points 12, 11, 10, and 13, and the others are 0. For the accumulative OPN, point 1 has the largest value of three times, and the corresponding point 12 on the right-side wall, which is at the same level as point 1, has an OPN value of two times. The accumulative OPN of the two corresponding points on each side of the wall is not completely equal to each other. For the OPC, point 3 has the largest value of 1.72, and its corresponding point has a value of 1.40. Similarly, the OPC of the two corresponding points are not equal. Although the values in the ordering of OPN and OPC are not completely subject to the sequence of the measuring point number, it also indicates that the overpressure phenomenon occurred concentratedly in the lower part of the ore pass.

When e = 1.0 m, there are seven points occurring the overpressure on the left-side wall, which OPN in size descending order is point 1, 5, 6, 3, 2, 7, and 8, six points on the right-side wall is point 13, 12, 1, 14, 17 and 16 in descending order, and the others are 0. The OPC on the left-side wall in size descending order are points 5, 1, 6, 3, 2, 7, and 8; those on the right-side wall are points 13, 12, 14, 17, 1, and 16, and the others are 0. For the accumulative OPN, point 1 has the largest value of 8 times, the corresponding point 12 on the right-side wall has an OPN value of 5 times, and the largest value on the right-side wall is achieved 14 times. For the OPC, point 5 on the left-side wall has the largest value of 2.09, its corresponding point has a value of 1.74, and point 13 on the right-side wall has the largest value of 9.03. Similarly, the OPC of the two corresponding points are not equal. According to the distribution of OPN and OPC, the overpressure phenomenon concentrates mainly in the lower part of the ore pass.

When e = 1.5 m, point 1 to point 4, point 6 and point 7 on the left-side wall occurred overpressure phenomenon, where point 2 has the largest OPN of 16times and the largest OPC of 4.83; point 10, point 12 to point 14, point 16 and point 17 on the right-side wall occurred overpressure phenomenon, where the point 12 has the largest OPN of 13 times and the point 13 has the largest OPC of 9.03. According to the distribution of OPN and OPC, the overpressure phenomenon is still found to be concentrated mainly in the lower part of the ore pass.

In summary, the change in the eccentricity e of the drawing port greatly influences the lateral pressure of each measuring point on both sides of the ore pass. Based on the ore drawing, when eccentricity e = 0.0 m, it is found that the increase of eccentricity e will affect the distribution characteristics of the maximum OPC and OPN, resulting in the asymmetric distribution of lateral pressure on both sides of the shaft wall. The overpressure phenomenon of each measuring point is mainly concentrated in the lower part of the ore storage section.

Under the same condition of the ore drawing times, the less the OPN, the smaller the OPC, and the lowest degree of damage to the ore pass wall. Therefore, from the perspective of OPN and OPC based on the analysis on Table 3, the damage degree of the ore pass wall under each eccentricity is e = 1.5 m > e = 1.0 m > e = 0.0 m > e = 0.5 m.

Conclusions

The conception of the eccentricity of the drawing port is introduced to describe the position of the ore drawing port in an ore pass, which reflects the eccentric distance from the drawing port center to the ore pass centerline.

A labeled-particle layers method is used based on numerical simulation to investigate the flow characteristics of solid bulk; it can clearly observe the change of the flow pattern of particles when ore drawing at the bottom of the ore pass.

The eccentricity of the drawing port has a certain influence on the ore-rock flow characteristics in the ore pass. Still, the influence is mainly concentrated in the range of the drawing funnel and less in the storage section of the ore pass. It is found that during ore drawing process under different eccentricities, the flow pattern of the topmost labeled particle layers is always in a “—”-shaped distribution, and the others in the shaft transform gradually from “—” shapes to a “U”-shaped distribution, and further gradually to a “V” shape when the layer is closer to the drawing funnel; when the eccentricity e = 0 m, the flow pattern of ore-rock particles in the storage section and drawing funnel is axisymmetrically distributed in a “V” shape with the centerline of the ore pass. With the increase of the eccentricity e, the flow pattern of ore-rock bulk, which is in the range of from the connection of the ore pass shaft and drawing funnel to the drawing port, gradually becomes an italic “V” shape, and its tip slants to the steeper sidewall of the drawing funnel.

The stress characteristics of both sides of the storage section wall are analyzed under different eccentric distances of the drawing port. It was found that the dynamic load caused by the ore-rock flow mainly acts in the lower part of the storage section. When the eccentricity e = 0.5 m, the accumulative OPN, and the maximum OPC are the smallest, so the damage degree of the ore pass wall is the lowest.

Author contributions

Software, formal analysis, data curation, writing–original draft, Z.D.; Software, investigation, resources, formal analysis, data curation, C.M; Resources, data curation, visualization, Q.M.; Methodology, formal analysis, writing–review and editing, project administration, funding acquisition, Z.X.; Conceptualization, methodology, writing–review and editing, supervision, project administration, funding acquisition, Z.L. All authors have read and agreed to the published version of the manuscript. All authors reviewed the manuscript.

Funding

The work was supported by the National Natural Science Foundation of China (Grant No.51774176, Grant No. 52204137), the Natural Science Foundation of Liaoning Province (Grant No. 2022-BS-281), and the Outstanding Young Scientific and Technological Talents Project of Liaoning University of Science and Technology (Grant No. 2023YQ10).

Data availability

All relevant data are within the manuscript. If you have any questions, please don’t hesitate to contact Zhiguo Xia at the address below. Email: xzgyy88@163.com.

Competing interests

The authors declare no competing interests.

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

These authors contributed equally: Zhe Deng and Chi Ma.
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