Analysis of dust pollution effect after blasting and dust removal parameters under hybrid ventilation in digging face

In order to reduce the dust pollution produced by metal mine tunneling after blasting operations, as well as to solve the optimization problem of hybrid ventilation and dust removal parameters, to enhance the working conditions at the construction site and safeguard the health of workers, a study was conducted focusing on a metal mine in Yunnan. The study developed a hybrid ventilation model for roadway blasting and tunneling, using Fluent software to examine airflow distribution, dust dispersion, and sedimentation behavior in the tunnel. The study also examined how varying distances between air inlets and outlets, as well as different air volumes, affect dust distribution under hybrid ventilation. Additionally, gray correlation analysis was used to examine the connection between the time needed to lower dust concentration to safe levels and the relevant influencing factors. Findings indicate that with hybrid ventilation, the airflow in the roadway is segmented into three zones: vortex, transition, and stable areas, and the average wind speed of the roadway section will show a trend of increasing and then decreasing, and then decreasing to about 0.22 m/s and gradually stabilizing. Before ventilation 1 min, dust diffusion speed is faster, after ventilation 1 min, dust diffusion speed is slower. Dust with particle size above 35 μm from blasting will be settled closer to the face, while dust particles smaller than 35 μm are carried away by the airflow or extracted from the tunnel due to the influence of the wind. Through comparative analysis, it can be seen that the air outlet of the press-in type wind pipe is 10 m away from the face of the excavation, when the air inlet of the exhaust-type wind pipe is positioned 5 meters from the excavation face, the ventilation and dust removal efficiency is significantly improved. Additionally, a pressure-to-extraction ratio (m) of 0.8 to 1 yields better dust control results. Their respective gray correlation coefficients are 0.732, 0.648, 0.630, and 0.621.To enhance the post-blasting environment in the roadway, optimizing hybrid ventilation and dust removal parameters should prioritize adjusting the air volume at the outlet of the press-in type wind pipe to improve dust removal efficiency.

1 Introduction

With the rapid development of China’s economy, the consumption of metal mineral resources continues to rise. To address the increasing need for mineral resources across society, mining operations are expanding in both intensity and depth. However, tunneling activities such as drilling, blasting, and excavation often generate significant amounts of dust, with post-blasting dust being particularly severe (Jiang et al., 2021a). This poses a major risk to production safety and the health of front-line workers.

In order to solve the dust pollution problem after blasting in the face, scholars at home and abroad have carried out a lot of research on the dust transport law in the roadway (Sun et al., 2018; Li et al., 2022; Chen et al., 2018; Geng et al., 2017; Zhang et al., 2020; Sun et al., 2021; Wang et al., 2019), and used field tests, experimental analysis and numerical simulation to study the influencing factors. Toraño et al. (2011) investigated the dust behavior of two auxiliary ventilation systems under time-dependent effects using a fluid dynamics model, and predicted the airflow distribution and dust dispersion patterns across various road sections at the working face, dust source locations, and behind the working face. Zhang et al. (2022) conducted numerical simulations to investigate the distribution patterns of dust particles with varying sizes under specific operating conditions, and to evaluate the effects of adjusting air supply velocity on dust distribution. Wen et al. (2023) examined how the position of the pressure pumping cylinder and the pressure-to-exhaust ratio affect dust distribution patterns, optimizing hybrid ventilation parameters based on these findings. Yu et al. (2018) and Chu et al. (2023), applying gas-solid two-phase flow theory, analyzed dust movement under various ventilation methods, offering insights for ventilation strategy selection. Meanwhile, Wei et al. (2020) and colleagues combined scaled experiments with numerical simulations to explore airflow and dust transport characteristics at different wind pipe heights. Qiao (2019) analyzed the dust distribution law under the long-pressure and short-pumping ventilation mode to solve the problem of high dust concentration in the roadway of tunneling. Hu et al. (2019) applied wind-dust flow theory to analyze coal seam excavation in high-gas coal beds, comparing simulation outcomes with actual measurements. Jiang et al. (2021b), Jiang et al. (2023) applied gas-solid two-phase flow theory to model the pollution effects of dust in tunneling faces, using numerical simulations to analyze how high altitudes influence dust transport dynamics. Nie et al. (2015) and others, in order to improve the ventilation and dust removal effect of long-pressure and short-drawing face, determined the optimal wind speed through simulation experiments, and studied the law of dust diffusion. Xing (2005) examined how the distance between the press-in and draw-out wind pipes and the working face influences dust concentration distribution through experiments on pressure-drawing hybrid ventilation. In addition, there are also scholars for the location of the dust source (Chen et al., 2022), the relative humidity in the tunnel (Zhou et al., 2021) and other factors on the dust transport and diffusion law. In summary, current research on dust transport patterns in mine tunnels primarily focuses on identifying influencing factors in dust transport at comprehensive coal mining and tunnel excavation workfaces, yielding a series of significant findings. These achievements hold great importance for ensuring coal mine safety and dust control operations. However, due to differences in mine types, metal mining excavation techniques diverge from coal mining practices. Metal mines predominantly employ blasting methods, whereas coal mines utilize roadheaders for cutting and excavation. Consequently, ventilation approaches and flow field distributions differ: coal mines implement ventilation and dust removal concurrently with excavation, while metal mines conduct these operations after blasting is completed. Furthermore, the distinct differences in ventilation and dust removal parameters significantly impact the dilution efficiency of blasting dust and the effectiveness of dust exhaust within the tunnels.

This study focuses on a metal underground mine in Yunnan, utilizing Fluent fluid simulation software to create a roadway model based on the actual conditions of the mine shaft. It simulates the airflow distribution, dust dispersion, and sedimentation patterns following blasting in tunneling operations. The research investigates how hybrid ventilation affects dust distribution under varying inlet/outlet distances and air volumes. Additionally, Grey correlation analysis is employed to examine the relationship between inlet/outlet air volume, distance, and changes in dust concentration.

2 Mathematical and physical modeling

2.1 Mathematical model

2.1.1 Turbulence model

The k-ε turbulence model is ideal for predicting flat-wall boundary layer flow, pipe flow, channel flow, and nozzle flow. It is known for its broad applicability, reasonable accuracy, and low computational cost. Given the complex and turbulent nature of the flow field at the excavation face, the k-ε turbulence model can effectively simulate transient changes in turbulent flow.

The continuity equation is shown in Equation 1.

$\rho \left(u·\nabla \right)·u=\nabla ·\left\{-pl+\left(\mu +{\mu }_T\right)·\left[\nabla u+{\left(\nabla u\right)}^T\right]\right\}+F=0(1)$

In Equation 1, $\rho$ is the density, kg/m³; $u$ is the wind speed, m/s; $-pl$ is the Reynolds stress, N; $\mu$ is the laminar viscosity coefficient, Pa-s; ${\mu }_T$ is the turbulent viscosity coefficient; $F$ is the other external forces, N; $\nabla u$ denotes the gradient for u; $\nabla$ (·) denotes the dispersion.

Assuming the gas within the system is incompressible, the equation for turbulent kinetic energy k can be written as Equation 2.

$\rho \left(u·\nabla \right)·k=\nabla ·\left[\left(\mu +\frac{{\mu }_T}{{\sigma }_k}\right)·\nabla k\right]+P_k-\rho ·\epsilon (2)$

In Equation 2, k is the turbulent kinetic energy, J; ${\sigma }_k$ is the Prandtl coefficient of the turbulent kinetic energy; $\nabla k$ denotes the gradient for which k is sought; $P_k$ is the turbulent kinetic energy generation term due to the mean velocity gradient; and $\epsilon$ is the dissipation rate.

The turbulent dissipation rate equation is shown in Equation 3.

$\left\{\begin{array}{l}\rho \left(u·\nabla \right)·\epsilon =\nabla \left[\left(\mu +\frac{{\mu }_T}{{\sigma }_k}\right)·\nabla \epsilon \right]+c_{\epsilon 1}·\frac{\epsilon }{k}·P_k-c_{\epsilon 2}·\rho ·\frac{{\epsilon }^2}{k}\\ {\mu }_T=\rho ·c_{\mu }·\frac{k^2}{\epsilon }\\ P_k={\mu }_T·\left\{\nabla u:\left[\nabla u+{\left(\nabla u\right)}^T\right]\right\}\end{array}\right.(3)$

In Equation 3, ${\sigma }_{\epsilon }$ is the Prandtl coefficient of the dissipation rate.

2.1.2 Discrete phase model

The forces acting on dust particles within mine tunnels are highly complex. Since the density of dust particles is significantly greater than that of air, their buoyancy effects can be disregarded. Consequently, they can be calculated using the trailing force model as Equation 4.

$\left\{\begin{array}{l}{F}_D=\frac{1}{{\tau }_p}·m_p·\left(u-v\right)\\ {\tau }_p=\frac{4{\rho }_p·d_p^2}{3\mu ·C_D·R{e}_r}\\ C_D=\frac{24}{R{e}_r}·\left(1+\frac{3}{16}R{e}_r\right)\\ {Re}_r=\frac{\rho ·\left|u-v\right|·d_p}{\mu }\end{array}\right.(4)$

In Equation 4, $F_D$ is the trailing force, N; ${\tau }_p$ is the shear stress, N; $m_p$ is the mass of the particle, kg; $u,v$ is the wind speed and particle speed, m/s; ${\rho }_p$ is the particle density, kg/m³; $d_p$ is the diameter of the particle, μm; $\mu$ is the kinetic viscosity of the gas, Pa·s; $C_D$ is the coefficient of trailing force; ${Re}_r$ is the Reynolds number; and $\rho$ is the fluid density, kg/m³.

2.2 Physical modeling and meshing

2.2.1 Physical model

Space Claim software is employed to build a tunnel model with a three-centered arch design, featuring a 5-m-wide cross-section, a peak height of 3.77 m, and a 50-m length. The hybrid ventilation model, illustrated in Figure 1, positions the press-in air blower on the left side of the tunnel,0.2 m from the left wall, with a diameter of 0.8 m. The extractor tube is placed on the right side,0.2 m from the right wall, with a diameter of 0.6 m. The press-in air duct is located 10 m from the excavation face, while the extractor air duct is positioned 5 m from the excavation face.

Figure 1

Figure 1. Physical model and meshing.

2.2.2 Mesh division

Meshing software is employed to divide the excavation face into grids, with the air inlets of the press-in and extractor-type wind pipes designated as velocity inlet boundaries, and the roadway end set as a pressure outlet boundary. The mesh configuration is illustrated in Figure 1.

2.2.3 The mesh independence test

Before running the simulation, it is essential to verify the mesh independence of the model. Using ICEM CFD software, the two physical models are meshed, generating three schemes with varying mesh densities for each model, as detailed in Table 1.

Table 1

Table 1. Mesh division of different ventilation methods.

During tunnel ventilation, airflow within the mine shaft is the primary factor influencing dust dispersion. Consequently, changes in wind speed and dust concentration serve as key indicators for assessing grid independence testing. To evaluate this metric, monitoring points were selected along the tunnel axis at a height of 1.5 m (within the breathing zone) to observe wind speed and dust concentration variations, serving as parameters for grid independence verification. Simulations were conducted using three grid schemes to obtain wind speed and dust concentration distributions under different grid densities, as shown in Figure 2. Results indicate that the trends in wind speed and dust concentration for all three schemes are fundamentally consistent, exhibiting a characteristic pattern of initial increase followed by decrease. This aligns with the requirements for independence verification. Balancing computational accuracy and efficiency, a grid size of 0.3 was ultimately selected for the grid partitioning.

Figure 2

Figure 2. Mesh independence test (a) Comparison of wind speed distribution (b) Comparison of dust concentration distribution.

2.3 Boundary conditions and discrete phase parameterization

2.3.1 Boundary condition setting

Drawing on the core principles of turbulence and particle motion in numerical simulations, and aligning with the real-world conditions of the excavation face, the model’s boundary conditions and fundamental solution parameters are configured. These boundary conditions are outlined in Table 2 and the solution parameters are outlined in Table 3.

Table 2

Table 2. Boundary condition setting.

Table 3

Table 3. Solution parameter settings.

2.3.2 Discrete phase parameter setting

Using the core principles of the discrete phase model in simulations and the actual conditions of the excavation face, the dust source’s position, dimensions, particle size range, and initial speed are specified. The discrete phase parameters are detailed in Table 4.

Table 4

Table 4. Discrete phase parameter setting.

3 Analysis of simulation results

3.1 Analysis of the wind flow field in the excavation tunnel

The tunnel’s wind flow field distribution greatly affects dust dispersion. Blasting-generated dust is transported by airflow, spreading from the excavation face to other areas. Thus, studying the wind flow field and its patterns helps explain dust dispersion. Numerical simulation reveals airflow patterns under mixed ventilation, as shown in Figure 3. Airflow near the excavation face is highly complex. To better understand this,11 cross-sections are created within the 50-m tunnel, with multiple measurement points to calculate average wind speed per section. Measurement point arrangement and average wind speed trends are displayed in Figure 4.

Figure 3

Figure 3. Trace diagram of tunnel wind flow

Figure 4

Figure 4. Trend of cross-section mean wind speed.

From Figure 3: (1) High-speed fresh airflow from the press-in wind pipe outlet targets the excavation face, forming a high-speed wall jet. However, due to the obstruction of the excavation face and the press-in wind pipe’s placement on the left side of the roadway, the airflow is deflected toward the wall, primarily moving toward the lower right side of the roadway. Additionally, the suction effect of the extracting wind pipe causes the airflow to curve, with some of it forming eddies in the area between the two wind pipes. This results in a vortex zone within 0∼10 m from the excavation face. (2) Another portion of the airflow from the press-in wind pipe is deflected at its outlet by the extracting wind pipe, moving backward along the left side of the roadway wall. This causes reduced airflow in the 5∼15 m region behind the press-in wind pipe. Due to the press-in wind pipe’s placement on the left side, the airflow is further deflected after hitting the pipe, primarily flowing toward the lower right side of the roadway. The airflow lines become highly complex, spiraling backward through the roadway, creating a transition zone 10–30 m from the excavation face. (3) The mixed ventilation system, combined with the suction effect of the extracting wind pipe, results in a more intricate overall airflow pattern in the roadway. After exiting the transition zone, the airflow slows and gradually stabilizes, forming a stabilization zone where the wind flow becomes consistent.

From Figure 4: In the vortex zone, tunnel wind speed first rises and then falls, staying in the high-speed range. The extracting wind pipe’s suction effect creates a peak speed of 2.15 m/s near its inlet. In the transition zone, complex airflow streamlines lead to a gradual decline and stabilization of wind speed. In the stabilization zone, airflow becomes steady, with wind speed holding at around 0.22 m/s.

3.2 Analysis of dust diffusion pattern after blasting in the excavation face

After simulating and analyzing the continuous airflow phase in the tunnel, the discrete phase model is enabled, with a jet source placed at the excavation face. A plane at the 1.5-m breathing zone height is selected for analysis, producing dust dispersion cloud diagrams at different times, as shown in Figure 5. The relationship between dust diffusion distance and time is also analyzed and fitted, as illustrated in Figure 6.

Figure 5

Figure 5. Variation of dust mass concentration in 1.5 m breathing zone with time.

Figure 6

Figure 6. Variation of dust Dispersal distance with time.

From Figures 5, 6, the following can be observed: (1) Under the influence of the press-in wind pipe, dust generated after blasting at the excavation face moves toward the roadway exit over time, while the pull-out wind pipe rapidly reduces dust concentration near the excavation face. After 5 s of ventilation, dust spreads to the area near the inlet of the extraction-type wind pipe. By 15 s, it reaches within 2 m of the outlet of the press-in wind pipe. After 60 s, dust disperses to the middle of the roadway, and by 120 s, it reaches the roadway exit. (2) The press-in wind pipe causes airflow to carry dust, gradually filling the entire roadway and expanding the dust distribution range. However, the area with dust concentration exceeding 100 mg/m³ begins to decrease after 60 s and nearly disappears by 180 s. Dust near the excavation face is extracted by the pull-out wind pipe, reducing the concentration in the breathing zone to around 100 mg/m³ after 60 s and almost completely removing it by 120 s (3) Fitting analysis reveals that dust spreads faster toward the middle of the roadway within the first 60 s of ventilation, while its movement toward the rear section slows down after 60 s.

3.3 Characterization of dust deposition after blasting in excavation face

Blasting in roadways generates significant amounts of dust with varying particle sizes. Gravity causes dust particles of varying sizes to display unique transport patterns. To study these characteristics, dust particles ranging from 1 to 100 μm are selected for simulation, revealing their settling patterns over time, as illustrated in Figure 7. Additionally, Figure 8 shows particle size distribution across various roadway cross-sections during tunneling.

Figure 7

Figure 7. Transport of dust with time for different particle sizes.

Figure 8

Figure 8. Particle size distribution of different sections in the excavation channel.

From Figures 7, 8, the following observations can be made: (1) Larger blasting-generated dust particles settle near the excavation face under gravity, while particles under 35 μm stay airborne due to turbulence and are eventually expelled by the wind. (2) Dust transported by airflow within the roadway after blasting ranges in size from 1 to 100 μm. Larger particles tend to accumulate and settle on the return side of the airflow, while smaller particles remain airborne and are carried out of the roadway. Over time, particles larger than 35 μm gradually settle on the ground and move slowly toward the roadway exit under the influence of airflow. (3) Near the excavation face, the particle size distribution is wider, with larger particles dominating. As particles move toward the exit, larger ones settle to the roadway floor, while smaller ones, unable to settle due to their low mass, remain airborne.

4 Optimal ventilation and dust removal parameters

4.1 Comparison of dust removal effect at different air inlet and outlet distances

As the hybrid ventilation method involves one press-in and one pull-out wind pipe, two simulation groups are designed for comparative analysis. The specific configurations are outlined in Table 5, where l_y represents the distance from the press-in wind pipe outlet to the excavation face, and l_c denotes the distance from the pull-out wind pipe inlet to the excavation face.

Table 5

Table 5. Setting the distance of hybrid ventilation ducts from the digging face.

4.1.1 Comparison of the dust removal effect of press-in type wind turbines at different air outlet distances

To comprehensively and reasonably analyze the impact of the press-in wind pipe’s distance on dust removal efficiency, the study selects distances of 5,10,15, and 20 m from the excavation face for the press-in wind pipe outlet, while fixing the pull-out wind pipe inlet at 5 m from the excavation face. The analysis focuses on the time when the roadway’s airflow stabilizes, revealing the dust concentration distribution in the roadway after 1 min of ventilation for different press-in wind pipe outlet distances, as illustrated in Figure 9.

Figure 9

Figure 9. Distribution of dust concentration in the roadway with different air outlet distances from the press-in wind pipe. (a) I_y = 5m (b) I_y = 10m (c) I_y = 15m (d)I_y = 20m.

From Figure 9, the following observations can be made: (1) As the distance between the press-in wind pipe outlet and the excavation face increases, the jet’s wind speed diminishes due to air resistance, resulting in a slower reflux speed but a larger reflux area. The jet and reflux also become more dispersed. (2) With increasing distance from the press-in wind pipe outlet, dust concentration in the vortex zone rises, while it decreases in the transition and stable zones. This is likely because the interaction between the jet and reflux intensifies, expanding the vortex range near the excavation face and making dust discharge in this area more gradual. (3) During ventilation, dust concentration near the excavation face increases as the press-in wind pipe outlet moves farther away, while the opposite trend occurs in the section from the wind pipe to the roadway exit. Therefore, reducing the distance between the press-in wind pipe outlet and the excavation face enhances the dust removal efficiency of the pull-out wind pipe, lowers dust concentration near the excavation face, and improves the blasting operation environment.

4.1.2 Comparison of dust removal effect under different air inlet distances of extractor type wind pipe

To comprehensively and reasonably analyze the impact of the extraction-type wind pipe’s inlet distance on dust removal efficiency, the study selects distances of 3,4,5, and 6 m from the working face for the extraction-type wind pipe inlet, while fixing the press-in wind pipe outlet at 10 m from the working face. The analysis focuses on the time when the roadway’s airflow stabilizes, revealing the dust concentration distribution in the roadway after 1 min of ventilation for different extraction-type wind pipe inlet distances, as illustrated in Figure 10.

Figure 10

Figure 10. Distribution of dust concentration in the roadway with different intake distances of extractor wind turbines. (a) I_c = 3m (b) I_c = 4m (c) I_c = 5m (d) I_c = 6m.

From Figure 10: (1) As the extraction-type wind pipe inlet moves farther from the working face, the suction area grows, but wind speed near the face drops due to air resistance, lowering suction efficiency. (2) As the extraction-type wind pipe inlet distance increases, dust concentration in the vortex zone rises, while it drops in the transition and stable zones. This is likely because the suction effect concentrates dust in the vortex zone, reducing its dispersion into the transition and stable zones. (3) During ventilation, the dust concentration near the working face decreases as the distance between the press-in wind pipe outlet and the working face increases, while the opposite trend occurs in the section from the wind pipe to the roadway exit. Therefore, appropriately increasing the distance between the extraction-type wind pipe outlet and the working face enhances dust removal efficiency, reduces dust concentration near the working face, and improves the blasting operation environment.

To provide a clearer analysis, the dust mass concentration in the roadway section was simulated, and the average concentration changes along the roadway section for different inlet and outlet distances after 1 min of ventilation are shown in Figure 11.

Figure 11

Figure 11. Mean concentration along the cross section of the ventilated 1 min roadway with different inlet and outlet air distances. (a) Distance of different air outlets from excavation face (b) Distance of different air inlets from excavation face.

From Figure 11, it is evident that under mixed ventilation conditions, high dust concentration areas exist in tunnels with varying inlet and outlet distances. For varying inlet distances of the extraction-type wind pipe, high concentration zones mainly lie at the vortex-transition boundary, with peak concentration differences reaching up to 578.9 mg/m³. In contrast, for different outlet distances of the press-in type wind pipe, the high concentration areas are situated in different locations, with a smaller peak difference of 502.1 mg/m³. Comparing the two simulation groups, the optimal ventilation and dust removal effect is achieved when the press-in type wind pipe outlet is 10 m from the excavation face and the extraction-type wind pipe inlet is 5 m from the excavation face.

4.2 Comparison of dust removal effect under different inlet and outlet air volume

To address the issue of increased dust settlement and low discharge efficiency in mine excavation faces, optimizing the inlet and outlet air volumes can effectively dilute and remove blasting fumes and dust in the roadway. Two simulation experiments are designed for the hybrid ventilation system to conduct a comparative analysis, with specific configurations outlined in Table 6. Here, v_y represents the air velocity at the outlet of the press-in wind pipe, v_c denotes the air velocity at the inlet of the extraction-type wind pipe, Q_y is the air volume at the outlet of the press-in wind pipe, Q_c is the air volume at the inlet of the extraction-type wind pipe, and m is the pressure-to-extraction ratio.

Table 6

Table 6. Hybrid ventilation duct air velocity settings.

4.2.1 Comparison of dust removal effect under different air flow rate of press-in type wind turbine

The air volume supplied by the fan is an important technical parameter in the process of tunnel construction, and the reasonable ventilation air volume is favorable for diluting and discharging the dust in the tunnel. Therefore, the inlet air volume of the pull-out fan is fixed at 1447.6 m³/min, and the outlet air volume of the press-in fan is selected as 965.1, 1206.4, 1447.6, 1688.9, 1930.2 m³/min.

The analysis focuses on the time when the tunnel’s airflow stabilizes, revealing the dust concentration distribution in the tunnel after 1 min of ventilation for different press-in fan outlet air volumes, as illustrated in Figure 12.

Figure 12

Figure 12. Distribution of dust concentration in the roadway with different air flow rates of the pressurized air duct outlet. (a) $Q_y=$965.1 m³ ${\min }^{-1}$ (b) $Q_y=$1206.4 m³ ${\min }^{-1}$ (c) $Q_y=$1447.6m³ ${\min }^{-1}$ (d) $Q_y=$1688.9m³ ${\min }^{-1}$ (e) $Q_y=$1930.2 m³ ${\min }^{-1}$.

From Figure 12, it can be observed that with the air volume at the inlet of the extraction-type wind pipe (Q_c) held constant, as the air volume at the outlet of the press-in wind pipe (Q_y) increases, the pressure-to-extraction ratio rises, and the wind speed of the press-in fan airflow also increases. However, the strong jet effect near the excavation face disrupts airflow distribution, leading to wider dust dispersion and reduced dust control efficiency under airflow influence.

4.2.2 Comparison of dust removal effect under different inlet air volume of extractor type wind pipe

The inlet air volume of the extraction-type fan is a key technical parameter in roadway construction, as an appropriate air volume ensures effective dust removal. To analyze this, the press-in fan’s outlet air volume is fixed at 1447.6 m³/min, while the extraction fan’s inlet air volumes are set at 965.1,1206.4,1447.6,1688.9, and 1930.2 m³/min.

The analysis focuses on the time when the roadway’s airflow stabilizes, revealing the dust concentration distribution in the roadway after 1 min of ventilation for different extraction-type fan inlet air volumes, as shown in Figure 13.

Figure 13

Figure 13. Distribution of dust concentration in the roadway with different intake air flow rates of extractor wind turbines. (a) $Q_c=$965.1 m³ ${\min }^{-1}$ (b) $Q_c=$1206.4 m³ ${\min }^{-1}$(c) $Q_c=$1447.6 m³ ${\min }^{-1}$ (d) $Q_c=$1688.9 m³ ${\min }^{-1}$ (e) $Q_c=$1930.2m³ ${\min }^{-1}$.

From Figure 13, it is evident that with the air volume at the outlet of the press-in wind pipe (Q_y) constant, as the air volume at the inlet of the extraction-type wind pipe (Q_c) increases, the pressure-to-extraction ratio decreases, and the airflow velocity of the extraction-type fan for dust removal rises. This causes an increase in dust concentration near the extraction-type fan but reduces dust concentration in the tunnel behind the press-in fan. The dust dispersion range also narrows, enhancing the dust removal efficiency.

To provide a clearer analysis, the dust mass concentration in the roadway was simulated, with average concentration changes along the section after 1 min of ventilation for varying inlet and outlet air flows shown in Figure 14.

Figure 14

Figure 14. Mean concentration along the roadway section for 1 min of ventilation with different inlet and outlet air flow rates. (a) Different outlet air volumes for Press-in blower (b) Different inlet air volumes for extractor blower.

From Figure 14, it can be observed that the dust removal effect is optimal when the pressure-to-extraction ratio m is between 0.8 and 1. However, when m < 1, the press-in air volume is smaller than the extraction air volume, causing airflow from the press-in fan to re-enter the extraction-type fan, resulting in airflow recirculation. This leads to higher dust concentrations near the extraction-type fan, requiring careful adjustment to ensure the extraction fan meets dust removal requirements.

4.3 Analysis of the degree of influence of ventilation and dust removal parameters

To optimize the ventilation and dust removal parameters in the roadway, Grey correlation analysis was employed to evaluate the impact of inlet/outlet distances and air volumes on reducing dust concentration to safe levels. Grey correlation analysis assesses correlation and influence by comparing system features and trends of key factors. The numerical simulation results are presented in Table 7, where X₀ represents the time required to reduce dust concentration to the safe threshold within 50 m of the excavation face, serving as the reference sequence to characterize dust diffusion and transport after blasting. X₁ and X₂ denote the outlet distance and outlet air volume of the press-in fan, respectively, while X₃ and X₄ represent the inlet distance and inlet air volume of the extraction-type fan, respectively, acting as the comparison sequences.

Table 7

Table 7. Data on the main factors influencing safe time.

The steps of the analysis are as follows:

1. Calculation of the initial value of the columns: Creation of the matrix $X=\left(X_0,X_1,X_2,X_3,X_4\right)$$=\left(\begin{array}{c}{X}_0\left(1\right)\\ X_0\left(2\right)\\ ⋮\\ X_0\left(15\right)\end{array}\begin{array}{c},\\ ,\\ ,\\ ,\end{array}\begin{array}{c}{X}_1\left(1\right)\\ X_1\left(2\right)\\ ⋮\\ X_1\left(15\right)\end{array}\begin{array}{c},\\ ,\\ ,\\ ,\end{array}\begin{array}{c}{X}_2\left(1\right)\\ X_2\left(2\right)\\ ⋮\\ X_2\left(15\right)\end{array}\begin{array}{c},\\ ,\\ ,\\ ,\end{array}\begin{array}{c}{X}_3\left(1\right)\\ X_3\left(2\right)\\ ⋮\\ X_3\left(15\right)\end{array}\begin{array}{c},\\ ,\\ ,\\ ,\end{array}\begin{array}{c}{X}_4\left(1\right)\\ X_4\left(2\right)\\ ⋮\\ X_4\left(15\right)\end{array}\right)$

2. Dimensionlessness of the series: Each measure represents a different meaning and needs to be dimensionless. The polarization method is used to process the series to obtain the dimensionless matrix $X^{\prime }=\left(X_0^{\prime },X_1^{\prime },X_2^{\prime },X_3^{\prime },X_4^{\prime }\right)$, k = 1, 2 , … , 15; i = 1, 2, 3, 4. The calculations are as follows: $X_i^{\prime }\left(k\right)=\frac{X_i\left(k\right)-\mathit{min}{X}_i}{\mathit{max}{X}_i-\mathit{min}{X}_i}$

3. Sequence Difference Calculation: Calculates the absolute difference between each comparison sequence and the corresponding element of the reference sequence one by one,referring to $\left|X_0^{\prime }\left(k\right)-X_i^{\prime }\left(k\right)\right|$.Obtain the sequence difference matrix ${\Delta }_i=\left({\Delta }_1\left(k\right),{\Delta }_2\left(k\right)\right)$,k = 1, 2, … , 15.

4. Calculation of the two-level difference of the sequence: The maximum value of the difference of the sequence is $M=\underset{i}{\max }\underset{k}{\max }{\Delta }_i\left(k\right)$,the minimum value of the sequence difference is $m=\underset{i}{\mathit{min}}\underset{k}{\mathit{min}}{\Delta }_i\left(k\right)$.

5. Correlation coefficient calculation: according to the formula ${\zeta }_i\left(k\right)=\frac{m+\eta M}{{\Delta }_i\left(k\right)+\eta M}$.Get the gray correlation coefficient matrix $R_i=\left({\zeta }_1\left(k\right),{\zeta }_2\left(k\right),{\zeta }_3\left(k\right),{\zeta }_4\left(k\right)\right)$,where $\eta$ is the resolution factor, taken as 0.5.

6. Gray correlation calculation: gray correlation formula: ${\zeta }_i=\frac{1}{15}{\displaystyle \sum _{k=1}^{15}}{\zeta }_i\left(k\right)$,included among these,k = 1, 2 , … , 15; i = 1, 2, 3, 4. Surrogate data to obtain the correlation between the reduction of dust mass concentration to a safe value within 50 m and the factors, ${\overline{R}}_i=\left({\zeta }_1,{\zeta }_2,{\zeta }_3,{\zeta }_4\right)=\left(0.621,0.732,0.630,0.648\right)$.

The greater the gray correlation, the stronger the influence on dust transport after blasting at the excavation face, and vice versa. Based on the gray correlation analysis, the factors affecting the time required to reduce dust concentration to safe levels after blasting are ranked as follows: The press-in fan’s outlet air volume (X₂), the extraction fan’s inlet air volume (X₄), the extraction fan’s inlet distance from the excavation face (X₃), and the press-in fan’s outlet distance from the excavation face (X₁). Therefore, to improve the post-blasting construction environment using the hybrid ventilation method, priority should be given to adjusting the air volume at the wind pipe outlets to enhance dust removal efficiency.

5 Conclusion

1. Under mixed ventilation, the suction effect of the extraction-type wind pipe creates complex airflow patterns in the roadway, divided into vortex, transition, and stability zones. In the vortex zone, wind speed initially rises, peaks near the extraction-type wind pipe inlet, and then declines. In the transition zone, wind speed gradually decreases and stabilizes, while in the stability zone, it remains steady at 0.22 m/s.

2. In a mixed ventilation system, the press-in type wind pipe facilitates the movement of dust from the excavation face toward the roadway exit over time after blasting. Meanwhile, the pull-out type wind pipe significantly reduces the dust concentration near the excavation face. Dust disperses more rapidly toward the central section of the excavation roadway within the first minute of ventilation, while its spread to the rear section slows down after the first minute. After 1 minute of ventilation, dust dispersion in the rear section of the tunnel slows down. Larger blasting-generated dust particles settle near the excavation face under gravity, while particles under 35 μm stay airborne due to turbulence and are eventually expelled by the wind.

3. Reducing the distance between the press-in type wind pipe outlet and the working face or increasing the distance between the pull-out type wind pipe outlet and the working face can improve the dust removal efficiency of the pull-out type wind pipe. This minimizes interference between the press-in and pull-out type wind pipes, thereby enhancing overall dust removal performance. Comparative analysis reveals that optimal ventilation and dust removal are achieved when the press-in type wind pipe outlet is positioned 10 m from the excavation face and the pull-out type wind pipe inlet is 5 m away. A pressure-drawing ratio (m) of 0.8∼1 enhances dust removal efficiency.

4. The time needed to lower dust concentration to safe levels after blasting is most influenced by the press-in fan’s inlet air volume, followed by the extraction fan’s air volume and distance from the excavation face. The press-in fan’s distance has a smaller impact, with gray correlation coefficients of 0.732, 0.648, 0.630 and 0.621. To enhance the post-blasting environment in the roadway, optimizing hybrid ventilation and dust removal parameters should prioritize adjusting the air volume at the outlet of the press-in type wind pipe to improve dust removal efficiency.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

JL: Funding acquisition, Supervision, Writing – original draft, Writing – review and editing. CH: Methodology, Software, Writing – original draft, Writing – review and editing. WW: Funding acquisition, Writing – review and editing. XL: Software, Validation, Writing – review and editing. LT: Data curation, Writing – review and editing. FC: Formal Analysis, Writing – review and editing. YC: Software, Writing – review and editing.

Funding

The author(s) declared that financial support was received for this work and/or its publication. This research was funded by Yunnan Fundamental Research Projects (grant number 202201AU070110), Yunnan University of Finance and Economics Scientific Research Fund Project (grant number 2021D04), and the Key Research and Development Project of Yunnan Province (grant number 202003AC100002).

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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References

Chen, D. W., Nie, W., Cai, P., and Liu, Z. Q. (2018). The diffusion of dust in a fullymechanized mining face with a mining height of 7 m and the application of wet dust-collecting nets. J. Clean. Prod. 205, 463e476. doi:10.1016/j.jclepro.2018.09.009

CrossRef Full Text | Google Scholar

Chen, L. J., Ma, Y. Q., Mubarak, G., and Liu, G. M. (2022). Study on dust pollution law and ventilation optimization of roadway excavation and shotcrete simultaneous operation. J. Clean. Prod. 379 (P1), 134744. doi:10.1016/j.jclepro.2022.134744

CrossRef Full Text | Google Scholar

Chu, X. L., Wei, W., Long, Z. H., Jiang, C. W., Liu, Q., and Nie, W. (2023). Research on air flow and dust distribution law of heading face under different ventilation modes and air pressures. Saf. Coal Mine. 54 (02), 35–39. doi:10.13347/j.cnki.mkaq.2023.02.007

CrossRef Full Text | Google Scholar

Geng, F., Luo, G., Zhou, F. B., Zhao, P., Ma, L., Chai, H., et al. (2017). Numerical investigation of dust dispersion in a coal roadway with hybrid ventilation system. Powder Technol. 313, 260–271. doi:10.1016/j.powtec.2017.03.021

CrossRef Full Text | Google Scholar

Hu, S. Y., Liao, Q., Wang, H., Feng, G., Xu, g., Huang, Y., et al. (2019). Gas-solid two-phase flow at high-gassy fully mechanized within highgassy coal seam. J. China Coal Soc. 44 (12), 3921–3930. doi:10.13225/j.cnki.jccs.2019.1008

CrossRef Full Text | Google Scholar

Jiang, Z. A., Zeng, F. B., and Wang, Y. B. (2021a). Research status and prospect of dust pollution control in typical working places during mining and transportation of metal mines in China, 01. Ma'anshan City, Anhui: Metal Mine, 135–153.

Google Scholar

Jiang, Z. A., Yang, B., Zhang, G. L., Zeng, F. B., and Wang, Y. B. (2021b). Analysis of dust pollution effect of cutting dust and ventilation control parameters at the heading face in plateau mines. J. China Coal Soc. 46 (07), 2146–2157. doi:10.13225/j.cnki.jccs.jj21.0449

CrossRef Full Text | Google Scholar

Jiang, Z. A., Zeng, F. B., Feng, X., Zhang, G. L., Yang, B., and Wang, Y. B (2023). Dynamic model and influencing factors of dust pollution after blasting in high altitude tunnel. J. China Coal Soc. 48 (01), 263–278. doi:10.13225/j.cnki.jccs.Z022.1563

CrossRef Full Text | Google Scholar

Li, B., Hu, H., Long, Y., Zhan, S., Zhang, Z., Li, W., et al. (2022). Dust transport behaviour in the nanwenhe extra-large stepped underground metal mine stope. J. Clean. Prod. 372, 133699. doi:10.1016/j.jclepro.2022.133699

CrossRef Full Text | Google Scholar

Nie, W., Ma, X., Cheng, W. M., Zhou, G., and Liu, Y. H. (2015). Simulation experiment on the influence of ventilation conditions on dust diffusion in long pressure and short pumping face. J. Cent. S. Univ. 46 (09), 3346–3353. doi:10.11817/j.issn.1672-7207.2015.09.026

CrossRef Full Text | Google Scholar

Qiao, A. L. (2019). Dust distribution law and comprehensive dust reduction technology with long-pressure and short-pumping ventilation mode. Shandong coal. Sci. Technol. 2019 (11), 116–118. doi:10.3969/j.issn.1005-2801.2019.11.042

CrossRef Full Text | Google Scholar

Sun, B., Cheng, W. M., Wang, J. Y., and Wang, H. (2018). Effects of turbulent airflow from coal cutting on pollution characteristics of coal dust in fully-mechanized mining face: a case study. J. Clean. Prod. 201, 308e324. doi:10.1016/j.jclepro.2018.08.001

CrossRef Full Text | Google Scholar

Sun, Z., Chen, L., Yu, X., Liu, G., Pan, G., Li, P., et al. (2021). Study on optimization of shotcrete loading technology and the diffusion law of intermittent dust generation. J. Clean. Prod. 312 (No.244), 127765. doi:10.1016/j.jclepro.2021.127765

CrossRef Full Text | Google Scholar

Toraño, J., Torno, S., Menéndez, M., and Gent, M. (2011). Auxiliary ventilation in mining roadways driven with roadheaders: validated CFD modelling of dust behaviour. Tunn. Undergr. Space Technol. 26 (1), 201–210. doi:10.1016/j.tust.2010.07.005

CrossRef Full Text | Google Scholar

Wang, Z. W., Li, S. G., Ren, T., Wu, J. M., Lin, H. F., and Shuang, H. Q. (2019). Respirable dust pollution characteristics within an underground heading face driven with continuous miner – a CFD modelling approach. J. Clean. Prod. 217, 267–283. doi:10.1016/j.jclepro.2019.01.273

CrossRef Full Text | Google Scholar

Wei, J. P., Xu, X. Y., and Jiang, W. (2020). Influences of ventilation parameters on flow field and dust migration in an underground coal mine heading. Sci. Rep. 10 (1), 8563. doi:10.1038/s41598-020-65373-7

PubMed Abstract | CrossRef Full Text | Google Scholar

Wen, H., Mi, W. S., Fan, S. X., Xu, Y., and Cheng, X. (2023). Simulation study on crucial parameters of long-compressive and short-suction ventilation in large section roadway excavation of LongWangGou coal mine. Environ. Sci. Poll. Res. 30 (3), 6435–6453. doi:10.1007/s11356-022-22568-x

PubMed Abstract | CrossRef Full Text | Google Scholar

Xing, D. X. (2005). Discussion on the location of reasonable pumping wind pipe opening for hybrid ventilation in excavation. J. Min. Saf. Environ. Prot. (04), 25–27.

Google Scholar

Yu, H. M., Chen, W. M., Xie, Y., and Peng, H. T. (2018). Micro-scale pollution mechanism of dust diffusion in a blasting driving face based on CFD-DEM coupled model. Environ. Sci. Pollut. R. 25 (22), 21768–21788. doi:10.1007/s11356-018-1992-4

CrossRef Full Text | Google Scholar

Zhang, G. b., Zhou, G., Song, S. Z., Zhang, L. C., and Sun, B. (2020). CFD investigation on dust dispersion pollution of down/upwind coal cutting and relevant countermeasures for spraying dustfall in fully mechanized mining face. Adv. Powder Technol. 31 (8), 3177–3190. doi:10.1016/j.apt.2020.06.009

CrossRef Full Text | Google Scholar

Zhang, W., Xue, S., Tu, Q. Y., Shi, G., and Zhu, Y. (2022). Study on the distribution characteristics of dust with different particle sizes under forced ventilation in a heading face. Powder Techno 406, 117504. doi:10.1016/j.powtec.2022.117504

CrossRef Full Text | Google Scholar

Zhou, G., Zhang, L. C., Liu, R. L., Sun, B., Kong, Y., and Huang, Z. (2021). Numerical simulation investigation for the pollution characteristics of dust particles in the fully mechanized mining face under different air humidity conditions. J. Environ. Che. Engin. 9 (6), 106861. doi:10.1016/j.jece.2021.106861

CrossRef Full Text | Google Scholar