Stress Characteristics and Ground Support Application in the Short-Distance Mining Face Under a Loose Aquifer

Abstract

This study investigates the impact of weak water-rich aquifers overlying shallow-buried thin bedrock coal seams on mining support systems. By applying Terzaghi’s theory to the evolutionary characteristics of the overburden structure in loose aquifers, a mechanical model for load transfer from the aquifer is established, and a calculation formula for the maximum working resistance of the support is derived. The results are validated using field mine pressure data from the 1010–1 working face of Wugou Coal Mine. The findings show that the overlying load of the key stratum is positively correlated with the water pressure in the aquifer; the higher the water pressure, the greater the overlying load, which leads to increased instability of the key stratum and a higher likelihood of support crushing. Additionally, the thickness of the bedrock is negatively correlated with the aquifer water pressure load transfer coefficient, meaning that a thicker bedrock layer reduces the impact of the aquifer’s water pressure on the key stratum, with a critical thickness of 50 m. Moreover, the working resistance of the support is positively correlated with the water pressure, and the pressure intensity at the working face in the aquifer-covered area after grouting reconstruction is about 33% higher than in non-aquifer-covered areas. The results provide a theoretical basis for safe mining in similar geological conditions and offer guidance for the selection of support systems.

1. Introduction

Coal has been a cornerstone of China’s economic and social development, providing essential energy support Xu [1]. However, with shallow coal resources nearly exhausted, China is increasingly turning to deeper mineral resources for development Xie [2]. As some mines with depleting shallow coal reserves begin to explore shallow-buried thin bedrock layers, they face significant challenges. These challenges include the instability of overlying strata and the risks of mine water inrush and support crushing [3,4,5,6,7,8,9,10].

Previous studies have explored the effects of loose aquifers and shallow-buried thin bedrock on mining operations. Xu [11] developed methods for predicting and preventing water inrush disasters, utilizing field measurements and numerical simulations. Yang [12] proposed a mechanical model for a combined bearing structure in the Shandong mining area, demonstrating the practicality of overburden fracture. Liu [13] established a model for surface subsidence deformation, identifying critical thresholds for subsidence in different mining conditions. Liu [14] studied water inrush mechanisms in high-pressure unconsolidated layers using a ‘double-row fracture’ model. Other research has addressed surface cracks, fracture zones, and mine pressure, focusing on the influence of thick, loose layers over thin bedrock [15,16,17]. However, despite these advances, many studies still treat these factors in isolation and fail to integrate them into a cohesive framework. For instance, recent research on underground water dynamics in mining operations has highlighted the importance of addressing both natural and technogenic factors, such as the transformation of hydraulic conductivity in rock mass and the identification of patterns in technogenic water pressure fluctuations [18].

However, despite these developments, most studies still treat water dynamics, overburden behavior, and support system response as largely independent phenomena. There remains a critical gap in understanding how changes in aquifer water pressure directly affect overburden stability and support characteristics in thin bedrock mining faces. Without integrating these factors into a coupled framework, predictive models may underestimate the risk of catastrophic events such as support crushing, roof collapse, and sudden water inrushes.

This study addresses this gap by systematically analyzing the mechanisms of water and sand inrush disasters, establishing a mechanical model for water pressure load transfer in thin bedrock overlying loose aquifers, and investigating the interaction between the support system and surrounding rock. Additionally, a formula is derived for calculating the maximum working resistance of the support system, providing essential guidance for safe mining practices under similar geological conditions.

2. Methods

The Wugou coal mine (as shown in Figure 1) is a fully concealed deposit covered by Neogene and Quaternary loose layers. It can be divided into four containing areas (groups) and three aquicludes (groups) from top to bottom. The total thickness is about 255.00–289.83 m, with an average of 272.88 m. The 1010–1 working face is located in the west wing of the first mining area of Wugou Coal Mine. The central coal seam is 10 coal, with an average mining thickness of 4.8 m. There is 2.16–8.48 m of aluminum mudstone at 60 m above 10 coal. The length of the working face is 651.2 m, the length of the air roadway is 630.7 m, the inclination length is 155 m, the inclination angle is 3–15°, and the average inclination angle is 9°. The hydraulic support adopts the ZZ11000/24/50 D model. Above the working face, the 230 m long organic roadway and the 64 m long air roadway exist in a ladder-shaped distribution of the ‘four-containing’ water layer (as shown in Figure 2). The thickness of the ‘four-containing’ is 25.30–47.88 m, with an average thickness of 32.8 m. The average thickness of the water-bearing sand layer is 14.42 m. The lithology mainly comprises of gravel, clay gravel, coarse sand, medium sand, and clay sand, sandwiched between 0–4 layers of thin-layer clay with gravel, sandy, sandy clay, and calcareous clay. The water pressure of the aquifer is about 3 MPa. The water pressure of the aquifer is about 3 MPa, which is an estimated value based on field observations and hydrostatic calculations. This pressure represents the average pressure within the aquifer under natural conditions, influenced by factors such as the depth of the aquifer, the permeability of the surrounding geological formations, and the presence of any overlying water bodies. The 3 MPa value serves as a reference for understanding the stress conditions in the aquifer and is critical for evaluating potential water inrush or other hydraulic-related phenomena in the region.

In order to improve the upper limit of coal seam mining to achieve safe mining, Wugou Coal Mine adopts the method of segmented downward and split grouting to carry out grouting transformation on the ‘four-containing’. Its bottom bedrock weathering zone in the water-bearing section of the 1010–1 working face is to realize the purpose of drainage, sand fixation, and water plugging (Figure 3). After increasing the upper limit of mining, the working face is about 22 m away from the ‘four-containing’ water layer. The lithology of the 10 coal roofs is composed of fine sandstone, coarse sandstone, siltstone, and mudstone (Figure 4).

After grouting, the “four-containing” becomes a weak, water-rich, nearly drained Class III water body. In this context, a Class III water body refers to an aquifer or water-bearing zone with moderate permeability, where water is partially confined. Following the grouting process, the No. 4 aquifer and the weathered zone transformed from a typical aquifer into a loose pore, weak aquiclude. This means the grouted zone now exhibits low water content, with significantly reduced sand mobility, making it less prone to water-sand inrush events. The grouting treatment effectively decreased the permeability of the geological body, transitioning it to a nearly drained state, with limited water flow and a reduced risk of water-related hazards during mining activities [19]. The strength of the “four-containing” was improved to prevent water and sand inrush during underground mining, and the shallow “four-containing” coal pillar resources were liberated. After grouting, core samples from the “four-containing” and the bedrock weathering zone were taken, and physical tests were conducted. It was found that the slurry material formed a fixed skeleton structure within the aquifer, existing between particle pores in the form of layered cement blocks, vein cement, cement columns, and cement fragments (Figure 5). The cementation was intact, and the filling was dense, resulting in a strong grouting effect. As a result of the grouting treatment, the strength of the bedrock weathering zone increased by about 2 to 5 times (the grouting process and its effects are described in detail in Reference [19]). The improvement in strength not only stabilizes the bedrock but also significantly reduces the risk of water and sand inrush during underground mining. The dense filling and effective grouting prevent further degradation of the bedrock, enhancing both its structural integrity and resistance to weathering. Subsequent tests showed that the grouted area exhibited much lower permeability compared to untreated zones, further confirming the effectiveness of the grouting process in enhancing the stability and safety of the mining environment. Further discussions will compare the grouted and non-grouted zones in terms of strength, permeability, and mining safety. Based on the detection of water flow, permeability, and the amount of grouting, the average load acting on the bedrock was determined to be approximately 1.8 MPa. This value was derived from a series of laboratory tests conducted on core samples taken from the bedrock after grouting. The tests measured key parameters, such as the bedrock’s mechanical strength and its response to applied pressure. The 1.8 MPa represents the average strength of the bedrock in its enhanced state post-grouting, reflecting the effectiveness of the grouting process in improving the structural integrity of the bedrock and reducing the risk of water and sand inrush during underground mining.

3. Mechanics Model of Thin Bedrock Structure in the Loose Aquifer

3.1. Mechanism of Water and Sand Inrush and Load Transfer Characteristics of Pore Water Pressure in Loose Aquifer

The main reason for water and sand inrush in the working face is a thick loose layer above the coal seam, and there is a weak to medium water-rich gravel aquifer at the bottom of the loose layer [20,21]. Affected by the mining activities of the working face, the central control strata-key strata above the coal seam rotate, slide, lose stability, and break. Due to the existence of an aquifer in the loose layer, the aquifer plays a role in load transfer due to the influence of the skeleton characteristics, flow characteristics, and pore water pressure of the aquifer. At this time, the loose aquifer is transmitted to the lower bedrock in a uniform load, and the load does not decrease with the excavation of the coal seam [22,23]. When the thickness of the bedrock between the coal seam and the aquifer, that is, the thickness of the aquiclude, is thin, it is easy to induce the height of the water-conducting fracture zone, develop and penetrate the aquifer, and guide the inrush channel at the bottom of the loose aquifer [24,25,26]. If the working resistance of the roof provided by the support is not enough, it is easy to cause the support to be crushed. Under self-weight and aquifer water pressure, the rapid flow of the water-sand mixture is promoted, which induces the occurrence of water and sand inrush accidents in the working face, thus affecting the normal production of the working face (Figure 6).

3.2. Mechanical Model of Loose Aquifer and Key Stratum

According to the literature [19], it can be seen that the grouting modification of the four-containing area at the 1010–1 working face, while to some extent displacing the four-containing area, enhanced the strength of both the four-containing area and the bedrock weathering zone, thus reducing the occurrence of water inrush accidents. However, it has not completely displaced the four-containing area, which can be understood as weakening the water pressure of the overlying aquifer on the 1010–1 working face. The bedrock weathering zone has not yet formed a cohesive structure with the bedrock. If the upper limit of the working face is raised, the thickness of the overburden will inevitably decrease, and the overburden between the working face and the aquifer will transform into a thin bedrock structure. Additionally, because the primary control rock layer (key stratum) in this thin bedrock structure exhibits a single characteristic, there is only one key stratum, with no additional bearing structures above it. Therefore, the ‘Terzaghi’ load transfer theory can be applied to calculate the load acting on the key stratum [27]. This assumption posits that the upper part of the surrounding rock is loose with some cohesion, and its strength must meet the Mohr-Coulomb strength theory, with the loose body at the top of the surrounding rock likely to settle or collapse [28]. Its theoretical calculation of surrounding rock pressure is shown in Figure 7.

In Figure 7, dz is the micro-element; Z is the distance between the aquifer and the micro-element; H is the distance between the top of the key block B and the bottom of the aquifer; h₀ is the thickness of the key block B; q_s is the load acting on the key block B; σ_v is the surrounding rock pressure acting on the upper part of the micro-element; τ_s is the shear stress on both sides of the micro-element; σ_n is the normal stress acting on both sides of the element; 2a₁ is the key layer fracture step, m; and λ is the bedrock lateral pressure coefficient.

According to Figure 7, a micro-element on the key block B is taken, and the static equilibrium equation can be obtained:

$$2a_1\left({\sigma }_v+d{\sigma }_v\right)-2a_1{\sigma }_v+2{\tau }_{s}dz-2a_1\gamma dz=0$$

(1)

$$\left.\begin{array}{l}{\tau }_s=c+{\sigma }_n\tan \phi \\ {\sigma }_n={\sigma }_v\lambda \end{array}\right\}$$

(2)

In Formula (1): C and φ are the cohesion and internal friction angle of bedrock, respectively.

To simplify Formula (2) into Formula (1):

$$d{\sigma }_v={\displaystyle \frac{(a_1\gamma -c-\lambda {\sigma }_v\tan \varphi )dz}{a_1}}$$

(3)

Formula (3) is differentiated, and the expression form is changed to obtain:

$${\displaystyle \frac{d(a_1\gamma -c-\lambda {\sigma }_v\tan \varphi )dz}{a_1\gamma -c-\lambda {\sigma }_v\tan \varphi }}=-{\displaystyle \frac{\lambda \tan \varphi }{a_1}}dz$$

(4)

Formula (4) is solved to obtain:

$$a_1\gamma -c-\lambda {\sigma }_v\tan \varphi =C{e}^{-{\displaystyle \frac{\lambda \tan \varphi }{a_1}}z}$$

(5)

According to the boundary conditions z = 0 and σ_v = q_s, then the integral constant in (5) is:

$$C=a_1\gamma -c-\lambda q\tan \varphi$$

(6)

Here, let z = H, and bring Equation (6) into Equation (5); the expression of the load acting on the bedrock can be obtained:

$$q_s=q_{s1}+q_{s2}={\displaystyle \frac{a_1\gamma -c}{\lambda \tan \phi }}\left(1-e^{-{\displaystyle \frac{\lambda \tan \phi }{a_1}}H}\right)+q_0{e}^{-{\displaystyle \frac{\lambda \tan \phi }{a_1}}H}$$

(7)

In Formula (7), q_s1 is the weight of bedrock; q_s2 is the confined aquifer acting on the key block B load; H is the distance between the top of the key block B and the lower part of the confined aquifer, m; and q₀ is the water pressure of the aquifer, MPa.

In order to analyze the influence of aquifer water pressure on the key stratum, the mechanical parameters a₁ = 8 m, q₀ selected as 0.1, 0.5, 1, 1.5, and 2 MPa, H = 0~100 m, C = 0.1 MPa, tanφ = 0.2, and λ = 0.7 are brought into Formula (7) to calculate the load distribution map of different aquifer water pressures acting on the key block B. It can be seen from Figure 8 that the greater the water pressure of the aquifer in the loose aquifer, the greater the load acting on the key block, and the thickness of the overlying bedrock of the key stratum affects the water pressure load transfer of the aquifer. When the key stratum is far from the loose aquifer, the influence of the water pressure of the aquifer on the key stratum is more minor. After the key stratum is 50 m away from the loose aquifer, the influence of the water pressure of the aquifer disappears. At this time, the load borne by the key stratum is the weight of the overlying bedrock.

During the mining of the working face with thin bedrock overlying a loose aquifer, the unique characteristics of the thin bedrock make it particularly vulnerable under the substantial water pressure from the aquifer. This pressure can easily destabilize the ‘masonry beam’ structure formed by the key stratum. If we exclude the potential for water and sand inrush, a crushing accident could occur if the maximum working resistance of the hydraulic support selected for the working face is unable to withstand the load transmitted by the instability of the key stratum. Therefore, it is crucial to understand the interaction between the key stratum and the support load to prevent such accidents.

3.3. Bracket-Key Stratum Mechanical Model

When mining under a thin bedrock coal seam, due to the close distance between the top of the 10 coal seam and the bottom of the key stratum in the 1010–1 working face, under the influence of working face mining, the key stratum of the roof breaks periodically, and the block degree of bare roof rock is close to 1 (i = h/l). When the fracture occurs, the hinged rock beam forms a short ‘masonry beam’ structure. Therefore, the analysis method of the key block of the masonry beam structure is adopted to establish the mechanical model of the short masonry beam structure in the key stratum [29], as shown in Figure 9.

The boundary conditions for this model include the application of overburden load at the top of the key stratum to simulate the weight and pressure from the overlying rock. The bottom boundary is assumed to be solid bedrock, fixed to simulate support. Lateral pressure is modeled using a lateral pressure coefficient, which is influenced by geological conditions and mining depth. If groundwater is present, hydrostatic pressure is applied to the water-bearing strata. Displacement constraints are set at both the top and bottom boundaries to limit deformations, reflecting the support provided by the surrounding materials.

It can be seen from Figure 9 that the relationship between the subsidence W₁ of the key block B in the goaf and the direct roof thickness Ʃh, the mining height M, and the rock bulking coefficient K_p is shown in Formula (8):

$$W_1=M-\left(K_p-1\right){\displaystyle \sum h}$$

(8)

According to the geometric relationship of the contact after the rotation of the rock block in Figure 10 [29,30], the approximate height of the extrusion contact surface at the end angle of the rock block can be calculated by Equation (9):

$$a={\displaystyle \frac{1}{2}}\left(h-l_1\sin {\theta }_1\right)$$

(9)

In Formula (9): a is the height of the contact surface, m; θ₁ is the rotation angle of key block B, °; l₁ is the length of key block B, m; h is the thickness of the key block, m.

Because the contact stress at both ends of the rock block is equal and the contact is plastic-hinged, the position of the horizontal thrust T action point in Figure 10 can be taken at 0.5a. The stress condition of the rock mass is related to the length of the rock mass, but the basic conditions of the periodic fracture of the rock mass are consistent. Therefore, assuming that l₁ = l₂ = l, ƩM_A and ƩM_C are taken as 0 in Figure 6, and R₂ = P₂, Equation (10) is:

$$Q_B\left(l\cos {\theta }_1+h\sin \theta +l_1\right)-P_1\left(0.5l\cos {\theta }_1+h\sin {\theta }_1\right)+T\left(h-a-W_2\right)=0$$

(10)

$$Q_B=T\sin {\theta }_2$$

(11)

In Formula (11): θ₂ is the rotation angle of the key block C, °; T is horizontal thrust, kN.

$$Q_A+Q_B=P_1$$

(12)

W₁ = lsinθ₁ and W₂ = l(sinθ₁ + sinθ₂) can be obtained through the geometric relationship. The whole structure calculates the displacement law sinθ₂ = 0.25sinθ₁, and the block size of the main roof rock block is i = h/l. Combined with Equations (6)–(8), the horizontal thrust T and the shear force Q_A between the main roof rock block and the unbroken rock block in front are obtained:

$$T={\displaystyle \frac{P_1}{i-0.5\sin {\theta }_1}}$$

(13)

$$Q_A={\displaystyle \frac{4i-3\sin {\theta }_1}{2(2i-\sin {\theta }_1)}}{P}_1$$

(14)

$$P_1=B\left({\gamma }_{1}h+q_s\right)l$$

(15)

According to the theory of ‘masonry beam’ structure, to prevent the sliding instability between rock blocks, the balance of the structure must meet the following conditions:

$$T\tan \phi +P_H\ge Q_A$$

(16)

Substituting Equation (13) and Equation (14) into Equation (16), it can be concluded that the support resistance P_H required to prevent the sliding instability support of the ‘voussoir beam’ structure is:

$$P_H\ge Q_A-T\tan \phi$$

(17)

In Formula (17): φ is the internal friction angle of bedrock, °.

According to Formulas (10)–(17), when the bedrock collapses periodically, the load on the support is the sum of the self-weight of the immediate roof and the support resistance provided to prevent the instability of the support, as shown in Formula (18):

$$P=P_Z+P_H={\gamma }_1{h}_Z{l}_{Z}B+{\displaystyle \frac{4i-3\sin {\theta }_1}{2\left(2i-\sin {\theta }_1\right)}}B\left({\gamma }_{1}h+q_s\right)l-{\displaystyle \frac{B\left({\gamma }_{1}h+q_s\right)l}{i-0.5\sin {\theta }_1}}\tan \phi$$

(18)

In Formula (18): h_z is the immediate roof thickness, m; γ₁ is the bulk density of bedrock, kN/m³; h is the key stratum thickness, m; l_z is the direct roof span, m; B is the width of the shield, m; q_s is the load acting on the key layer, MPa; and l is the breaking step, m.

The relationship between the water pressure of different aquifers and the working resistance of the support is calculated by Formula (18), as shown in Figure 11. In addition to the active controllable parameters, only considering the water pressure of the aquifer, it is found that the larger the pore water pressure, the greater the load acting on the key stratum, and the greater the load transmitted to the support when the key stratum breaks. It can be seen that the working resistance of the support is closely related to the load transfer of the overlying rock structure, and the load transfer of the overlying rock structure is directly related to the water pressure of the aquifer. The overlying bedrock on the working surface is subjected to a significant water pressure of the aquifer, making breaking the key layer easy. If the working resistance provided by the support is lower than the load transferred by the overburdened rock breaking, the support will be crushed. The phenomenon indirectly reveals the mechanism of crushing the loose aquifer’s thin bedrock structure’s working face and further highlights the importance of support selection.

4. On-Site Mine Pressure Distribution and Theoretical Verification

4.1. On-Site Mine Pressure Data Analysis

Through the occurrence characteristics and mining conditions of the overlying strata on the 1010–1 working face of Wugou Coal Mine, the three-dimensional graphics of the working resistance of the support and the advancing distance of the working face are drawn, as shown in Figure 12. It can be seen that under the condition of thin bedrock mining, with the continuous advancement of the working face, the overburden fracture of the stope presents periodic collapse. The average working resistance of the hydraulic support of the working face presents periodic changes. When mining in the grouting transformation section above the thin bedrock, the roof weighting frequency of the working face is high, the resistance is significant, and the step distance is small. The periodic weighting step distance is about 6~18 m, and the average weighting step distance is about 12 m; when mining under the loose layer of thin bedrock, the roof weighting frequency of the working face is low, the working resistance is small, the periodic weighting step distance is significant, the periodic weighting step distance is about 13~21 m, and the average weighting step distance is about 16 m.

In order to analyze the stress on the hydraulic supports in both the water-bearing and non-water-bearing areas of the working face, we selected the maximum working resistance of each hydraulic support in these two areas and used this data for comparison. From Figure 13, it can be observed that during mining in the grouting section of the working face, the working resistance of the hydraulic support fluctuates around the rated value of 40 MPa. Specifically, the working resistance exceeds 45 MPa for 10.64% of the time, falls between 40 and 45 MPa for 9.57%, and is below 40 MPa for 79.79%. This shows that in the grouting section, the hydraulic support continues to endure high working resistance values, with a significant portion of time exceeding the rated 40 MPa. In contrast, when mining in the loose layer area, the working resistance is generally lower than the rated 40 MPa. Specifically, only 2.13% of the time does the support exceed 40 MPa, 3.19% of the time it falls between 35 and 40 MPa, and 94.68% of the time it is below 35 MPa, indicating that the hydraulic support operates at much lower resistance levels in the non-water-bearing area. From this comprehensive analysis, it is evident that the roof pressure in the grouting transformation area is generally around 40 MPa, while in the loose layer area, the roof pressure is approximately 30 MPa. This suggests that the roof pressure in the grouting-transformed area is about 33% higher than in the loose layer area. The calculation for this difference is as follows: 40 MPa (grouting area roof pressure) − 30 MPa (loose layer area roof pressure) = 10 MPa, and 10 MPa/30 MPa = 33%. Thus, the roof pressure in the grouting-transformed area is approximately 33% higher than in the loose layer area.

4.2. Theoretical Calculation

According to the geological data of the 1010–1 working face, it can be seen that about 1.8 MPa reduces the water pressure of the aquifer after grouting. Therefore, the parameters 2a₁ = 12 m, q₀ = 1.8 MPa, H = 2.5 m, C = 0.1 MPa, tanφ = 0.2, λ = 0.7, l = 12 m, l_z = 5.038 m, γ₁ = 0.025 kN/m³, B = 1.66 m, sinθ₁ = 0.03 obtained from the field, geological data are brought into Formula (18) to calculate that the support resistance provided by the support should be greater than 41.87 MPa when the roof is broken. In order to prove the reliability of the theoretical calculation, by selecting the maximum working resistance data of each hydraulic support during the mining of the four-containing area of the 1010–1 working face, the maximum working resistance distribution map is drawn as shown in Figure 14. It can be seen that during the mining period, the load transmitted to the support when the roof is pressed fluctuates around 40 MPa and only 20.21% exceeds the maximum working resistance of the support. The rest is less than the maximum working resistance. Comparing the theoretical calculation value with the field data, it can be seen that the theoretical calculation value (41.87 MPa) is 17% lower than the measured mine pressure value (max 51.35 MPa) in the local area of the working face. The reason is that the actual working face roof pressure is complex, and many factors exist. For example, the existence of the dip angle of the coal seam causes the pressure generated by the instantaneous fracture of the roof in the local high section of the working face to be higher than the pressure in the low section. The local rock mass of the roof of the working face is broken, which leads to the working resistance acting on the hydraulic support when the roof pressure in the local area is higher than the rated working resistance of the hydraulic support. However, 57.45% of the working resistance of the hydraulic support on site is distributed between 35 and 40 MPa, and the load less than 40 MPa accounts for 79.79%, and the safe mining is realized on site. Therefore, to ensure safety, the author believes that in selecting support for similar working faces, the selection of support by increasing 30% based on theoretical calculation can provide a good guiding significance for determining support for identical working faces.

4.3. Discussion

The Terzaghi load transfer theory is widely applied in geotechnical engineering, particularly in mining and tunnel construction, to predict the behavior of surrounding rock under stress. The theory aligns with the Mohr-Coulomb strength criterion, which accurately models the mechanical characteristics of surrounding rock, especially in loose and cohesive materials, which is consistent with the thin bedrock structure at the 1010–1 working face. In practice, this theory has been successfully used to predict settlement and collapse, and assess the need for additional reinforcement. However, the Terzaghi theory makes several simplifying assumptions, such as assuming the surrounding rock is homogeneous and isotropic. These assumptions may not hold true under complex geological conditions, as the surrounding rock can vary in type and contain fractures. Furthermore, the Terzaghi theory does not account for dynamic loading conditions such as seismic activity or operational dynamics, which could influence the surrounding rock’s response. In areas with complex geological structures, such as soft overburden over hard bedrock, the model may oversimplify the interaction between layers, leading to inaccuracies. Additionally, the theory assumes that the surrounding rock has a certain cohesion, but in fractured or highly weathered conditions, the cohesion may be much lower than expected, resulting in lower stability.

In the context of the current research, especially in coal mining regions dealing with loose aquifers, significant challenges exist, but these areas also present opportunities for sustainable development. Loose aquifers have traditionally been viewed as a risk in coal mining, particularly in terms of water inrush and rock instability, which can lead to water flooding, ground subsidence, or even mining accidents. However, with technological advancements, loose aquifers are no longer merely seen as problems but as unique opportunities for innovative multi-product coal mining. Recent research shows that coal mines can be transformed into multi-product complexes, where coal production is complemented by the extraction of clean water, methane, thermal energy, and secondary raw materials. This model aligns with Environmental, Social, and Governance (ESG) principles [31,32].

This innovative approach integrates technological advancements to enhance coal mining sustainability while reducing environmental impact. Proper management of loose aquifers can turn water-bearing layers into valuable resources, such as reusing mining water for circulation or supplying treated water to nearby communities. Methane gas captured during mining can be converted into clean energy, lowering greenhouse gas emissions and reducing the mine’s energy consumption. Additionally, using secondary raw materials such as slag and tailings reduces dependence on natural resources and creates economic value. This approach promotes resource efficiency and supports the long-term sustainability of mining regions.

Through these innovative operations, loose aquifers are no longer seen as environmental hazards but as resources that can contribute to the sustainable development of mining areas when effectively managed. Therefore, in mine management, loose aquifers should be regarded as potential resources rather than obstacles. With scientific management and technological innovation, loose aquifers can be effectively utilized to support the sustainable development of mining regions. In this way, coal mines can maximize economic benefits while also promoting environmental restoration and protection, creating a positive cycle of economic, environmental, and social benefits. This integrated approach supports the transformation and upgrading of the coal mining industry, aligning with the increasingly stringent global requirements for sustainable development and environmental protection.

5. Conclusions

• The formation mechanism of water and sand inrush in thick unconsolidated layers is systematically summarized. Based on the load transfer model established using Terzaghi’s theory, it is identified that 50 m above the aquifer floor is the critical attenuation point for load transfer. Within this distance (H < 50 m), every 0.1 MPa increase in pore water pressure results in an approximate 0.08 MPa increase in the load on the key stratum. Beyond 50 m (H ≥ 50 m), the influence of pore water pressure becomes negligible, and the load is primarily governed by the self-weight of the overlying rock strata. Additionally, an increase in bedrock thickness can effectively reduce the load transfer coefficient of the aquifer.
• Based on the load transfer mechanics model of thin bedrock in loose aquifers, a calculation formula for the maximum working resistance of the support is derived using the short masonry beam structure model. The study shows a linear positive correlation between the aquifer and key layer water pressure and support resistance (R² > 0.95). When water pressure increased from 0 MPa to 2 MPa, the load in the key layer rose from 1.02 MPa to 2.64 MPa, representing a 159% increase. This underscores the critical importance of selecting appropriate support systems for working faces in the four-containing area.
• By analyzing the field hydraulic support data, it was found that the working resistance in the grouting modification area is approximately 79.79% lower than the rated working resistance, yet the working face still achieves safe mining conditions. The theoretical calculation results align with the distribution characteristics of the working resistance of the hydraulic support under roof pressure at the site, suggesting that these calculations can provide a reliable theoretical basis for selecting support systems in similar working faces. However, for safety considerations, it is recommended to increase the support capacity by 30% based on the theoretical calculations.