Research on Coordinated Technology for Coal Mining Progress and Roof Water Drainage at the Working Face

Abstract

To address the challenges of water hazard control in the thick water-rich sandstone aquifer of the roof under monoclinal structure conditions at Panel 110504 of Wangwa Coal Mine, as well as the problems of excessive ineffective drainage and high cost associated with the traditional full-face pre-drainage method, a study on the coordinated technology of mining progress and roof water drainage was carried out. By analyzing the geological and hydrogeological conditions of the panel, it was determined that the height of the water-conducting fracture zone reaches 228 m, which has penetrated the Yan’an Formation and entered the sandstone aquifer of the Zhiluo Formation, forming a unified composite water-filling source from the two aquifers. Based on calculations using the Theis equation and field drainage tests, the stable drainage time was determined to be 95 d and the advance drainage distance 300 m. Accordingly, a coordinated technical scheme of “sectional drainage while mining” was proposed, optimizing the layout parameters of drainage boreholes and the division of drainage sections. Field application results show that this technology reduced the average water inflow of the panel by 255.94 m³/h compared with the traditional mode, cumulatively saved 5.1413 million m³ of drainage water, cut drainage costs by 20.5652 million CNY, and no water hazard occurred. The research results can provide a technical reference for mining coal seams with water-rich roof under similar monoclinal structure conditions.

1. Introduction

Coal, as a crucial component of the energy structure, plays an irreplaceable supporting role in economic development. However, the complex hydrogeological problems encountered during coal mining—especially roof water hazards in water-rich coal seams—have become a key bottleneck restricting the safe and efficient mining of coal mines [1,2]. Roof water hazards not only easily trigger water inrush and gushing accidents, leading to casualties and equipment damage, but also significantly increase mine dewatering costs, cause waste of water resources, and exert irreversible negative impacts on the ecological environment of mining areas [3,4]. Therefore, developing efficient and economical technologies for roof water hazard prevention and control is an urgent demand for realizing safe and green coal mining.

Pre-drainage of roof water is one of the core technologies for active prevention and control of roof water hazards [4,5,6]. This technique involves pre-arranging drainage boreholes and constructing drainage systems to lower the water level and pressure in aquifers, thereby reducing water inflow during panel extraction at the source. It has shown remarkable effectiveness in complex conditions such as water-rich coal seams and extremely thick sandstone aquifers in the roof [7,8,9,10,11]. Current research on roof water pre-drainage mostly follows the principles of zonal control and dynamic regulation: differentiated drainage strategies are first determined based on aquifer water-richness zoning, and then prevention and control modes are formulated in combination with the spatiotemporal effects of drainage. Meanwhile, accurate prediction of water inflow is achieved by considering the permeability evolution of mining-disturbed rock masses, which guides the implementation of drainage engineering [12,13,14]. However, under specific geological conditions such as monoclinal structures and thick, water-rich sandstone aquifers, the traditional full-face pre-drainage mode exhibits obvious drawbacks. One-time drainage of the entire panel tends to result in excessive ineffective drainage, prolonged drainage cycles, and persistently high costs [15,16,17]. At the same time, with increasing mining depth and intensity, the complexity of water hazard prevention continues to rise, demanding higher precision and coordination in drainage technology [18,19]. How to dynamically couple panel mining progress with roof water drainage, achieving the goals of reducing water inflow and lowering energy consumption while ensuring safety, has become a critical scientific and engineering issue urgently needing resolution in the field of mine water hazard control.

The 110,504 working face of Wangwa Coal Mine is located in a typical monocline structural area. The sandstone aquifers of the Yan’an Formation and Zhiluo Formation in its roof are characterized by large thickness, strong water-bearing capacity and close hydraulic connection, which together form a unified composite water-filling source, posing an extremely prominent threat of roof water hazard. Aiming to elucidate the geological and hydrogeological characteristics of this working face, this paper systematically carries out research on the coordinated water reduction technology between mining progress and roof dewatering. Through systematic analysis of the working face’s geological structure, aquifer occurrence characteristics and development law of the water-conducting fracture zone, the water-filling source and main controlling factors of water hazard are clarified; combined with theoretical calculation using the Theis equation and on-site water release tests, key technical parameters such as stable dewatering time and advanced dewatering distance are determined; an innovative coordinated technical scheme of “segmented dewatering and simultaneous mining dewatering” is proposed, and the borehole layout parameters and segmented dewatering division scheme are optimized; and the feasibility and application effectiveness of the technical scheme are verified through numerical simulation analysis and on-site engineering application. The research results can provide important technical reference and engineering reference for the safe and efficient mining of coal seams with water-bearing roofs under similar monocline structural conditions.

2. Geological and Hydrogeological Conditions of the 110,504 Working Face

2.1. Working Face Overview

Wangwa Coal Mine is located in Guyuan City, Ningxia Hui Autonomous Region. The 110,504 working face belongs to the 11th mining area of the mine, mainly mining the No.5 coal seam of the Jurassic Yan’an Formation, and adopts the longwall full-thickness top-coal caving mining method along the strike. As shown in Figure 1, the working face is generally located in the southeastern area of the mine, adjacent to the 110,510 and 110,502 working faces in the west, and connected to the return airway, lower car yard and transport airway of the 11th mining area in the north. As shown in Figure 2, the coal seam elevation of the working face ranges from +1164.706 m to +1296.932 m, presenting a monocline shape with high northwest and low southeast, with a strike length of 2580 m, an inclined length of 192 m, and a coal seam thickness of 9–12 m. The structural conditions in the area where the working face is located are relatively simple, belonging to a typical monocline structure, with an average dip angle of rock strata of 8.3° and no large faults developed, which provides a relatively favorable structural basis for the smooth implementation of working face mining and dewatering schemes.

2.2. Hydrogeological Conditions

2.2.1. Aquifer Characteristics

The overlying strata on the roof of the No.5 coal seam in Wangwa Coal Mine are sequentially developed from bottom to top as the Middle Jurassic Yan’an Formation (J₂y), Middle Jurassic Zhiluo Formation (J₂z), Upper Jurassic Anding Formation (J₃a), Lower Cretaceous Yijun Formation (K₁y), Oligocene Qingshuiying Formation (E₃q) of the Paleogene, and Quaternary System (Q). The specific stratum sequence is shown in Figure 3.

The roof aquifers that play a dominant controlling role in the working face water hazards are the Yan’an Formation sandstone aquifer and the Zhiluo Formation sandstone aquifer. The detailed hydrogeological parameters of these two aquifers are listed in

Table 1. Hydrogeological parameters of the water-bearing aquifer in the roof of the 110,504 working face.

Aquifer	Permeability Coefficient (m/d)	Transmissivity (m2/d)	Storage Coefficient	Specific Yield	Unit Water Inflow (L/(s·m))	Water-Bearing Capacity
Yan’an Fm	0.329~1.75	12.0~31.5	2.06~2.87 × 10−4	0.065~0.123	0.13	moderate to strong
Zhiluo Fm	0.48~0.951	18.5~36.6	1.62 × 10−4	0.166	0.167	moderate

, and their hydrogeological characteristics are described as follows:

Yan’an Formation sandstone aquifer: This aquifer has a thickness of 10–30 m, with a vertical distance of 0.5–20 m from the roof of the No.5 coal seam. Its lithology is dominated by fine sandstone, with a porosity of 12–15%. Based on the downhole water release test data of the 110,504 working face, its permeability coefficient is measured to be 0.480–0.951 m/d, and the water-bearing capacity grade is medium.

Zhiluo Formation sandstone aquifer: This aquifer has a thickness of 50–150 m, with a vertical distance of 70–80 m from the roof of the No.5 coal seam. Its lithology is pebbly coarse sandstone with loose cementation and a porosity of 15–20%. Determined by downhole water release tests, its permeability coefficient is 0.329–1.75 m/d, and the water-bearing capacity grade can reach medium to strong.

2.2.2. Hydraulic Connection of Aquifers

A comprehensive technical method combining geophysical exploration, hydrochemical characteristic analysis and isotope testing was adopted to systematically determine the hydraulic connection between the Yan’an Formation and Zhiluo Formation sandstone aquifers. The research results show that the two aquifers have the same source of recharge, mainly relying on static reserves, without lateral or vertical recharge from other aquifers. The water quality monitoring data during the water release test indicate that the two aquifers have the same hydrochemical type, both being Cl·HCO₃-Na type; their pH value ranges are similar, between 7.8 and 8.9, and their total mineralization levels are equivalent, ranging from 1703 to 1976 mg/L. The above hydrogeological and hydrochemical characteristics fully confirm that the Yan’an Formation and Zhiluo Formation sandstone aquifers have close hydraulic connections and jointly form a unified composite water-filling aquifer system.

2.3. Structural Conditions and Development Characteristics of Aquifer Fracture Zones

The 110,504 working face is located in the middle section of the monocline structure in Wangwa Mining Area. The rock stratum strikes nearly north–south, and dips northwest, with a dip angle ranging from 5° to 12° and an average dip angle of 8.3°. The F2 reverse fault developed in the region is located at the western boundary of the working face, with a northeast strike, a dip angle of 70°, and a displacement greater than 150 m. This fault is a water-resisting fault and has little impact on the hydrogeological conditions of the working face.

No secondary faults are developed within the working face, and the rock stratum has good integrity, but primary fractures are relatively developed. The fractures are mainly tensile fractures perpendicular to the stratum plane, with a fracture spacing of 2–5 m and an extension length of 3–8 m. Some fractures penetrate the Yan’an Formation and Zhiluo Formation aquifers, serving as the main channels for groundwater migration.

Combined with the measured data of the development height of the water-conducting fracture zone in the mining area, numerical simulation results and similar model test data, the fracture–mining ratio for No.5 coal seam mining is determined to be 19. Based on the maximum mining thickness of 12 m in the working face, the development height of the water-conducting fracture zone is calculated to be 228 m. Analysis combined with the roof stratum structure shows that this fracture zone completely penetrates the Yan’an Formation sandstone aquifer and extends into the Zhiluo Formation sandstone aquifer, and both aquifers serve as direct water-filling sources for working face mining.

3. Cooperative Mechanism and Technical Solution for Water Extraction and Drainage

3.1. Research on Collaborative Mechanisms

3.1.1. Method for Determining Drainage Intervals

A method combining theoretical calculation using the Theis equation and on-site verification through downhole water release tests is adopted to determine the time required for dewatering to reach a steady flow state, providing time parameter support for the coordinated operation of mining and dewatering.

Based on the unsteady flow theory, the Theis equation is used to establish a calculation model for the time t required for borehole dewatering to reach a steady flow state, which is as follows:

$$t={\displaystyle \frac{{25r}^2{u}^{*}}{T}}$$

(1)

$$r=10S\sqrt{K}$$

(2)

where t is the time required for borehole drainage to reach a steady flow (d); u* is the storage coefficient; T is the transmissivity (m²/d); r is the radius of influence (m); K is the permeability coefficient (m/d); and S is the drawdown of the water level (m).

Combined with the actual hydrogeological conditions of the 110,504 working face, the initial water head elevation of the dewatering borehole is determined to be +1290 m, and the water head elevation to be controlled before working face mining is +1150 m. Considering that the working face is generally a monocline structure, the average water level drawdown S is calculated to be 70 m. The average values of the hydrogeological parameters of the Yan’an Formation and Zhiluo Formation sandstone aquifers are selected and substituted into the above formula for calculation, and the time required for the borehole dewatering to reach a steady flow state is finally obtained as t = 95 d.

To verify the reliability of the theoretical calculation results, three typical boreholes (8-1, 8-2, 8-3) in No.8 drilling site located in the middle of the transport gateway of the 110,504 working face were selected to carry out downhole water release tests. Continuous monitoring of the water inflow variation during borehole dewatering shows that the water inflow of the boreholes decays rapidly in the early stage and gradually stabilizes in the later stage, all reaching a steady state within 3 months, which is basically consistent with the theoretically calculated 95 d. This verifies the rationality and reliability of the stable dewatering time parameter (Figure 4).

3.1.2. Determination of Advance Clearance Distance

The advanced dewatering distance is a core spatial parameter to ensure the coordinated operation of working face mining and dewatering. Its value needs to be accurately matched with the stable dewatering time and working face mining speed so as to ensure that the roof aquifer has completed effective dewatering operations when the working face is mined to the target section.

Combined with the working face mining and excavation plan, the designed mining speed is determined as v = 3.05 m/d. Based on the stable dewatering time t = 95 d determined in Section 3.1.1, the “mining speed–dewatering time” coupling calculation method is adopted to derive the calculation formula for the advanced dewatering distance L, which is as follows:

L = v × t

(3)

Substituting the above parameters into the formula for calculation, we obtain L = 3.05 m/d × 95 d ≈ 300 m.

The calculation results indicate that dewatering operations need to be initiated 95 days in advance before working face mining, ensuring that mining operations always advance within the effective dewatering area with an advanced distance of 300 m. This parameter setting not only avoids the problem of ineffective water discharge caused by excessively long advanced dewatering distance, but also effectively prevents water hazard risks arising from excessively short distance, providing a reliable quantitative basis for the reasonable division of subsequent segmented dewatering sections (see Figure 5).

3.2. Collaborative Technical Solution Design

3.2.1. Spacing of Water Drill Holes

Combined with the monocline structural characteristics of the 110,504 working face, this study fully relies on and exerts the hydrogeological advantages of this structure, and selects to centrally lay dewatering boreholes in the transport gateway with relatively low terrain to improve dewatering efficiency.

The design of borehole construction parameters is as follows: the boreholes are arranged in an out-of-plane inclined manner, with the dip angle controlled between 40° and 45°, and the final hole elevation is set at +1290 m, ensuring that the boreholes completely penetrate the Yan’an Formation sandstone aquifer and extend into the Zhiluo Formation sandstone aquifer, so as to realize efficient dewatering of the target aquifers. The plane layout of boreholes follows the principle of uniform coverage, and the spacing between boreholes in the aquifer section is not more than 50 m, ensuring that the dewatering influence range is fully covered without blind areas.

Special drilling rigs for water exploration and drainage in coal mine underground are adopted for borehole construction. After hole formation, a 16-meter-long casing for hole wall protection is installed at the hole mouth, equipped with blowout prevention valves. After the completion of borehole construction, the hole mouth valves are closed and will be opened uniformly when entering the dewatering operation stage of the corresponding section, so as to avoid ineffective loss of water resources caused by early dewatering (Figure 6).

3.2.2. Open-Cut Section Division

Based on the 300 m advanced dewatering distance determined in Section 3.1.2 and combined with the 2580 m strike length of the 110,504 working face, this study adopts the division principle of “uniform segmentation and terminal adaptation” to divide the working face into eight independent dewatering sections along the strike direction.

Among them, the length of each of the first seven dewatering sections is set to 300 m, and the length of the last section is adaptively adjusted according to the remaining strike length of the working face, with a determined length of 480 m. The total length of the eight sections is exactly consistent with the 2580 m strike length of the working face. A set of independent dewatering boreholes is arranged corresponding to each dewatering section, and the control range of the boreholes is completely matched with the length of the corresponding section, forming a segmented dewatering pattern of “one section, one borehole group”. This realizes the step-by-step follow-up and coordinated advancement of dewatering operations and working face mining, ensuring the continuity and effectiveness of operations.

3.2.3. Collaborative Workflow

(1)

Based on the above segmented dewatering pattern, a coordinated operation process of “mining dewatering” is formulated, which is divided into five stages. The operation requirements and key points of each stage are as follows:

(2)

First-section advanced dewatering stage: A total of 95 days before the official mining of the working face, open all boreholes in the first 300 m dewatering section and start advanced dewatering operations. Simultaneously deploy real-time monitoring devices for water level, water pressure and water inflow to dynamically grasp the law of aquifer drawdown and ensure that the dewatering effect meets the preset safety standards.

(3)

Simultaneous mining and dewatering coordination stage: After the dewatering of the first aquifer section reaches a stable state, start the first-section mining operation of the working face. At the same time, open all boreholes in the second 300 m dewatering section to realize the synchronous operation mode of “mining the current section and dewatering the next section”. Strictly control the operation sequence to ensure that when the mining of the first section is completed, the dewatering duration of the second section is exactly 95 days, and the dewatering effect fully meets the mining safety conditions.

(4)

Step-by-step cycle advancement stage: Subsequent operations are carried out in a cyclic manner in accordance with the fixed mode of “mining the nth section + dewatering the (n + 1)th section” (n = 1, 2, …, 6). Always keep the working face mining operations within the safe section where effective dewatering has been completed, and eliminate water hazard risks from the source.

(5)

Final stage: When the working face is mined to the penultimate dewatering section, simultaneously open all boreholes in the last 480 m dewatering section to carry out dewatering operations. Ensure that when the working face advances to the final section, the aquifer in this area has completed the dewatering work for the specified duration, the dewatering effect meets the standards, and the safe and efficient advancement of the final mining operation of the working face is guaranteed.

4. Numerical Simulation Analysis of Synergistic Dilution Effects

4.1. Numerical Model Construction

To quantitatively analyze the dewatering effect of the coordinated technology of “segmented dewatering and simultaneous mining dewatering”, this study adopts the finite element numerical calculation software COMSOL (6.1) to establish a hydrogeological numerical model of the 110,504 working face (see Figure 7), and systematically carries out research on the evolution law of the seepage field under the combined action of mining and dewatering.

Combined with the actual geological and hydrogeological conditions of the working face, the scope and boundary conditions of the numerical calculation model are clarified: the upper boundary of the model is bounded by the +1290 m water level line; the left boundary extends 1500 m outward from the working face boundary; the lower boundary extends 2000 m outward from the working face boundary; and the right boundary takes the F2 reverse fault as the natural boundary. The model is trapezoidal in overall shape, with an upper base length of 6964 m, a lower base length of 10,259 m, a model height of 2459 m, and a total calculation area of 21.18 million m².

According to the regional hydrogeological characteristics, the boundary conditions of the model are set as shown in Figure 8, specifically as follows: (1) the upper boundary is set as a no-inflow boundary with a water pressure of 0 Pa; (2) the F2 reverse fault on the right side is a natural water-resisting boundary, which is set as a water-resisting boundary condition; and (3) the left boundary is a variable water head boundary. Combined with the average dip angle of 8.3° of the regional monocline structure, the water pressure calculation formula for this boundary is derived as (2459 − y) × 1460 Pa (where y is the vertical coordinate value of the model); (4) the lower boundary is set as an inflow boundary with a water pressure of 2459×1460 Pa.

Model parameters were selected to align with field conditions: the layout spacing of drainage boreholes in the plane was 50 m. The numerical simulation domain includes the aquifers of the Yan’an Formation and the Zhiluo Formation. The permeability coefficient of the Yan’an Formation is (0.329 + 1.75)/2 = 1.0395 m/d, and that of the Zhiluo Formation is (0.480 + 0.951)/2 = 0.7155 m/d. The study area represents a transition from unconfined to confined aquifer conditions. Its simplified aquifer structure model is shown in Figure 9. Accordingly, the permeability coefficients were assigned separately for three distinct aquifer zones in the roof:

In Zone ①, where only the Yan’an Formation is present in the roof, the permeability coefficient was set to 1.0395 m/d.

Zone ③ consists of the composite confined aquifers of the Yan’an and Zhiluo Formations. Given an average thickness of 75 m for the Yan’an Formation and 120 m for the Zhiluo Formation, the equivalent permeability coefficient under parallel flow conditions is calculated as (1.0395 × 75 + 0.7155 × 120)/(75 + 120) = 0.8393 m/d.

Zone ② comprises a composite of the confined Yan’an Formation and the unconfined Zhiluo Formation. Its permeability coefficient is determined as k = [75 × 1.0395 + (2459 − y − 514) × tan8.3° × 0.7155]/[75 + (2459 − y − 514) × tan8.3°] m/d.

Based on the aforementioned parameters and boundary conditions, the initial pore-water pressure distribution of the model was calculated, as shown in Figure 10. Controlled by the monoclinal structure, the pore-water pressure in the roof aquifer shows an increasing trend with greater burial depth of the coal seam.

4.2. Numerical Analysis Results

To visually characterize the dynamic evolution of aquifer pore pressure and saturation under the sectional drainage mode, contour maps of aquifer pore pressure (Figure 11) and aquifer saturation (Figure 12) corresponding to different drainage section lengths were plotted, respectively. The analysis shows that the variation trends in the two types of contour maps are highly consistent. When the aquifer water is effectively drained, its internal pore pressure drops to 0, and the saturation simultaneously decays to 0, which can serve as a core criterion for judging whether the drainage effect meets the standard.

The numerical simulation results indicate that by first activating drainage boreholes within a 400 m range in the open-off cut section, including eight boreholes on the haulage roadway side and boreholes outside the open-off cut, the first 300 m section of the working face can be completely dewatered. At this point, the mining operation for the first section of the working face is initiated, while the next set of six drainage boreholes is activated simultaneously. When the working face advances 300 m, the drainage effect for the newly added 300 m aquifer section reaches a stable state.

By advancing according to the cyclic mode of “mine one section, drain one section”, it can always be ensured that the mining area of the working face remains within the effective drainage range of 300 m ahead. When the working face advances to 2400 m, all remaining drainage boreholes are activated simultaneously, including the remaining boreholes on the haulage roadway side and boreholes outside the stopping line, to carry out drainage operations for the final 180 m section. This ultimately achieves safe drainage and mining for the entire working face.

To further verify the spatial distribution characteristics of the drainage effectiveness, pore pressure and saturation profiles along both the longitudinal section at the center of Panel 110,504 and the section parallel to the haulage roadway were extracted (Figure 13 and Figure 14). The characteristics of the curves indicate that the sectional drainage mode can achieve uniform dewatering of the aquifer within the panel and its boundary areas, effectively eliminating local water-rich hazards and ensuring safe mining operations.

Table 2. Numerical calculation results of water inflow for segmented dewatering.

Serial Number of Dewatering Section	Total Effective Span (m)	Total Water Inflow of Goaf and Dewatering Boreholes (m3/h)	Reduced Water Inflow Compared with Traditional Mode (m3/h)
1	300	38.22	463.31
2	600	70.64	430.89
3	900	111.09	390.44
4	1200	160.44	341.09
5	1500	217.91	283.62
6	1800	286.54	214.99
7	2100	366.08	135.45
8	2400	457.86	43.67
9	2580	501.53	0
Mean		245.59	255.94

presents the simulated total water inflow data from both the goaf and drainage boreholes for each drainage section. The data show that as the drainage section and mining scope expand simultaneously, the total water inflow gradually increases. The average water inflow during panel drainage is 245.59 m³/h, and the total water inflow peaks at 501.53 m³/h when panel extraction is completed. Compared with the traditional one-time full-panel drainage mode, the sectional drainage mode achieves an average water reduction of 255.94 m³/h, demonstrating a significant water-saving effect.

5. Field Application and Effect Evaluation

5.1. Field Application

The coordinated technology of “segmented dewatering and simultaneous mining dewatering” has been verified by on-site application in the 110,504 working face of Wangwa Coal Mine. Roadway excavation construction of this working face was initiated in April 2021, and it was officially transferred to the mining operation stage in March 2023. The full-face mining task was successfully completed in June 2025, with an overall mining cycle of 27.5 months.

Before the start of working face mining operations, the construction, acceptance and supporting equipment installation of all dewatering boreholes were fully completed. Combined with the working face section division plan, a total of 62 dewatering boreholes were constructed on site, with the plane layout spacing strictly controlled within 50 m. All boreholes penetrate the Yan’an Formation sandstone aquifer and extend into the Zhiluo Formation sandstone aquifer, fully meeting the preset dewatering depth requirements (see Figure 15 for the plane distribution of boreholes).

During the mining operation period, the coordinated operation process of “segmented dewatering and simultaneous mining dewatering” was strictly followed. The dewatering boreholes in the corresponding sections were opened one by one according to the actual advancing progress of the working face. Dynamic monitoring devices for water inflow, water pressure and water level were synchronously deployed to conduct real-time tracking and recording of key parameters throughout the dewatering process, ensuring accurate matching between the dewatering effect and the mining progress, and guaranteeing the safe and efficient advancement of mining operations.

5.2. Application Effect Evaluation

5.2.1. Effectiveness of Water Inflow Control

Relying on the on-site application of the coordinated technology of “segmented dewatering and simultaneous mining dewatering”, the 110,504 working face achieved precise prevention and control of roof water hazards, and no disasters such as roof water inrush or gushing occurred during the entire mining cycle. Only a small amount of dripping water appeared locally on the working face roof, which did not have any adverse impact on the mining operation efficiency and underground production safety.

The real-time water inflow monitoring data of the working face goaf and dewatering boreholes are shown in Figure 16. Comparative analysis results indicate that the actual water inflow of the working face is slightly higher than the normal water inflow predicted by numerical simulation. The main reason for the difference is that the release effect of aquifer static reserves was not fully considered in the numerical simulation process.

Although there is a slight deviation between the numerical simulation and on-site measured data, the variation trends of water inflow between the two are highly consistent, both showing the characteristic of “gradually increasing with the increase in dewatering sections and tending to be stable in the later stage”. This result not only verifies the rationality and reliability of the numerical simulation method adopted in this study but also indicates that the coordinated dewatering technology proposed in this research can effectively control the working face water inflow and achieve the expected application effect.

5.2.2. Economic Effectiveness Evaluation

Based on field application data and numerical simulation results, the economic benefits of the coordinated technology of “sectional drainage while mining” were quantitatively analyzed in terms of both reduced drainage volume and saved drainage costs.

Compared with the traditional one-time full-panel drainage mode, the average water inflow during sectional drainage at Panel 110,504 was 245.59 m³/h, while the projected inflow under the traditional mode was 501.53 m³/h. The average hourly water reduction reached 255.94 m³/h, representing a water reduction rate of 51%.

The total panel mining cycle was 27.5 months, equivalent to 837 days. Calculated on the basis of 24 h per day, the cumulative saved drainage volume is as follows:

255.94 × 24 × 837 = 5.1413 million m³.

The drainage cost at Wangwa Coal Mine mainly includes equipment depreciation, energy consumption, labor, etc. According to recent comprehensive accounting, the integrated mine drainage cost is 4 CNY/m³. Thus, the total drainage cost saved by applying this coordinated technology amounts to the following:

5.1413 × 4 = 20.5652 million CNY.

The sectional drainage mode avoids the long-term full-load operation of high-capacity drainage equipment required in the traditional full-panel drainage approach, significantly reducing indirect costs such as equipment depreciation, power consumption, and labor maintenance, thereby further enhancing the overall economic benefits of the technology application.

6. Conclusions

• The height of the water-conducting fracture zone at Panel 110,504 of Wangwa Coal Mine reaches 228 m, completely penetrating the Yan’an Formation and entering the sandstone aquifer of the Zhiluo Formation. The two aquifers are closely connected hydraulically, forming a unified composite water-filling source, which is the key target of roof water hazard control.
• By combining theoretical calculation using the Theis equation with verification through underground water-release tests, the stable drainage time for the roof aquifer of the panel was determined to be 95 d. Together with the designed mining speed of 3.05 m/d, the advance drainage distance was calculated as 300 m, providing key quantitative parameters for formulating the coordinated technical scheme.
• A coordinated technical scheme of “sectional drainage while mining” was proposed, dividing the panel along the strike into nine drainage sections. Drainage boreholes were arranged along the haulage roadway, and the operation was advanced following the mode of “mining the nth section + draining the (n + 1)th section”. This achieves the goal of 300 m advance drainage for the working face, effectively avoiding ineffective drainage.
• Field application results show that this coordinated technology can reduce the average water inflow of the panel by 255.94 m³/h compared with the traditional full-panel drainage mode, saving a cumulative drainage volume of 5.1413 million m³ and reducing drainage costs by 20.5652 million CNY. No water inrush or sudden water inflow occurred during the entire panel extraction process, achieving the dual goals of safe mining and cost-effective efficiency improvement.