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Article

Study on Seepage Effect of Roadway Based on Polyformaldehyde (POM) Fiber Concrete

by
Yongshuai Sang
and
Guangjin Wang
*
Faculty of Land Resources Engineering, Kunming University of Science and Technology, Kunming 650093, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(7), 3503; https://doi.org/10.3390/app15073503
Submission received: 18 January 2025 / Revised: 8 March 2025 / Accepted: 11 March 2025 / Published: 23 March 2025
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Abstract

:
This article presents the results of a study focused on enhancing the permeability resistance of roadways using polyformaldehyde fiber-reinforced concrete. The uniqueness of this study is its interest in polyformaldehyde fiber, which has not been widely studied in underground mining roadways, especially in relation to its impact on permeability resistance. The permeability resistance of polyformaldehyde fiber-reinforced concrete with different lengths (30 mm, 36 mm, 42 mm) and dosages (5 kg/m3, 7 kg/m3, 9 kg/m3) was tested by the step pressure method and seepage height method. The hydrostatic pressure and seepage height of polyformaldehyde fiber-reinforced concrete were analyzed, and the best polyformaldehyde fiber-reinforced concrete with the best permeability resistance was selected to carry out numerical simulation based on a phosphate mine in Yunnan Province. The changes in the pore water pressure, maximum principal stress, and displacement of the roadway’s surrounding rock under the influence of groundwater seepage were analyzed. The results show that the addition of polyformaldehyde fiber can effectively improve the impermeability of concrete. With the increase in length and dosage, the impermeability of the polyformaldehyde fiber concrete increases first and then decreases. Under ordinary support conditions, the surrounding rock of the roadway is affected by the seepage of groundwater over time, which leads to the roadway strength’s decline and creep deformation, necessitating the strengthening of the roadway’s anti-drainage measures. Under conditions of reinforcement with polyformaldehyde fiber concrete, the displacement of the top of the roadway obviously reduces, which can effectively improve the permeability resistance and stability of the roadway.

1. Introduction

Among the widely used materials in civil engineering, concrete is valued for its durability, tensile strength, and versatility [1,2]. Being moldable in different forms and sizes, it can find a wide variety of structural applications ranging from buildings and bridges to roadways [3,4,5]. In all its forms, plain concrete is, however, marred by intrinsic flaws, which have an adverse effect on its durability in the long term [6,7]. In this regard, it is distinguished by its tensile weakness, making it susceptible to tensile cracking, poor crack resistance, and excessive permeability, which can lead to the seepage of water and reduced durability in adverse weather conditions [8,9].
To mitigate such adversity due to the seepage of water, particularly in roadways and seepage areas, different methods have been proposed. Some of these methods include using geo-synthetic materials, drainage systems, and waterproofing membranes [10,11,12]. While such methods can reduce the seepage of water, each of these methods contains a drawback in relation to durability. Waterproofing membranes can degrade, geo-synthetic materials may not be locally compatible, and drainage systems may be obstructed [13,14,15]. Such drawbacks take us toward a more sustainable and effective solution for making roadways more resistant in such adverse circumstances.
To this end, the use of polymeric materials, such as polyformaldehyde fibers, is highly advantageous in relation to traditional methods. The fibers provide a stronger and flexible solution by reinforcing concrete for the prevention of water infiltration, enhancing its functionality in the long term, and making it compatible with various environmental factors [16]. Our solution is not only addressing short-term issues of the seepage of water, but it is also advantageous in making road infrastructure more sustainable and longer-lasting. For the further enhanced functionality of concrete, various fibers have been added to concrete to improve its mechanical properties and durability [17]. The fibers used in concrete production, depending on the type of material, are usually classified as metal fibers, polymer fibers, ceramic fibers, or natural fibers, with each reinforcing fiber having its own advantages and disadvantages [18,19]. The mechanical properties of fiber concrete have been studied, and steel, polypropylene, sisal, and polyformaldehyde (POM) fibers have been of interest due to their capability in enhancing concrete durability and mechanical properties. In a study, for example, steel fibers were analyzed for their contribution toward enhancing the mechanical properties of M30-grade concrete in terms of compressive and flexural strengths, using various contents of fibers. This study showed enhanced strengths, where fibers of 1% yielded a maximum compressive strength and 0.75% for flexural strength, emphasizing fibers’ capability in enhancing concrete performance [20]. Several similar studies have been conducted on synthetic and natural fibers in concrete, such as polypropylene and sisal fibers. Sisal fibers showed a 6% increase in compressive strength and a 4% increase in tensile strength due to their hygroscopic nature, while polypropylene fibers showed similar properties relative to a reference concrete. Sisal fibers, although lowering workability compared to polypropylene, showed a more environmental-friendly alternative, balancing between workability and strength [21]. Additionally, in 2023, Xiang Li et al. conducted research on the durability of concrete influenced by polyformaldehyde (POM) fibers. The outcomes showed that polyformaldehyde fibers enhanced compressive strength, enhanced splitting tensile strength, narrowed down pore diameter, and lowered porosity, making concrete compactness greater and contributing toward enhanced impermeability, sulfate corrosion, and frost resistance, which make polyformaldehyde fiber a material of interest for durability [22]. Mydin et al. in [23], lastly, talked about using polypropylene fibrillated fibers (PFFs) in foamed concrete. The outcomes indicated that the splitting tensile, compressive, and flexural strengths improved when using PFF in an optimal content of 3%. Beyond this level, though, there was a drop in strength due to a lack of a proper spread of fibers, which indicates there is a need for an effective spread of fibers for maximum usage in foamed concrete of a lightweight variety. Steel fiber can effectively increase the fracture toughness, crack resistance, and impact resistance of concrete; can maintain or even improve the strength; and has a certain ductility [24]. Afroughsabet et al. found that adding 1–1.5% volume steel fiber to concrete can increase the bending strength by 150–200%, tensile strength by 25–45%, and compressive strength by 10–25% [25]. Ashkezari GD et al. tested the mechanical properties of steel fiber concrete and found that a 3% volume of steel fiber could increase the tensile and flexural properties of concrete by 228% and 180% [26]. So far, steel fiber has been the most commonly used fiber-reinforced concrete material [27]. However, due to its material characteristics, steel fiber easily corrodes in aerobic humid environments and is not suitable for underground permeable roadway support [28,29]. Unlike steel fiber, polyformaldehyde fiber has not been extensively well researched in concrete in relation to underground mining, rendering this study highly novel. Different from steel fiber, polyformaldehyde fiber has the characteristics of high strength, high modulus, moderate elongation, dimensional stability, good water dispersion, and strong alkali resistance, and it shows great application potential in strengthening concrete materials [30,31,32]. Existing studies have shown that polyformaldehyde fibers are distributed inside concrete, which have higher sensitivity to various shrinkage cracks and a faster reaction speed [33,34,35]. Structural fibers in concrete can significantly reduce the formation of penetrating cracks, that is, greatly improve the crack resistance and permeability resistance of concrete. After concrete cracks under a load, polyformaldehyde fiber has the same residual bending strength or deformation energy absorption value as the steel mesh, that is, toughness. Therefore, it can effectively improve the flexural strength, splitting resistance, and cracking resistance of concrete [36,37].
As stress increases in confined environments, the influence of groundwater on material deformation becomes more evident [38,39]. Additionally, with the deepening of an underground roadway, the ground stress of the surrounding rock increases significantly, and the influence of groundwater on the deformation of surrounding particles like rock becomes more obvious [40]. On the other hand, the seepage volume force generated by groundwater changes the original rock stress state, whereas groundwater changes the mechanical properties of rock and reduces the strength of the rock mass [41]. Therefore, groundwater is an important factor in the analysis of rock deformation. In view of the seepage evolution law of a roadway’s surrounding rock under the joint action of the stress field and seepage field, scholars have conducted extensive research from the angle of mathematical modeling and simulation tests. Based on the theory of elastic–plastic damage mechanics, Peng, Zhang et al. established a regression model for the reasonable cover layer thickness of an underwater tunnel through a numerical simulation of fluid–structure coupling in an underwater tunnel [42]. Wang, Wei et al. used three-dimensional fluid–structure coupling numerical simulation to study the influence of the underlying cave on a shield tunnel crossing the sand layer [43]. Sun, Qin et al. investigated the different infiltration erosion modes induced by tunnel seepage in different strata types and analyzed the microscopic characteristics of these infiltration erosion modes [44].
The impermeability of concrete is an important factor affecting the life of a concrete structure. At present, the studies on the influence of polyformaldehyde fiber on concrete impermeability are relatively few, and the degree of influence is not clear. Therefore, through physical model tests and numerical simulations, the impermeability of polyformaldehyde fiber-reinforced concrete was investigated in this study, which provides an important scientific basis for the seepage prevention of polyformaldehyde fiber in a roadway. Thus, in this study, we added polyformaldehyde fiber to concrete to improve its impermeability. The impermeability of polyformaldehyde fiber-reinforced concrete was studied by the step pressure method and seepage height method. The influence of different lengths and dosages of polyformaldehyde fiber on the impermeability of concrete was measured. The mechanism of the influence of polyformaldehyde fiber on the impermeability of concrete was revealed by the establishment of a numerical model and by microstructural analysis. The results can not only provide technical support for the stability and safe production of the tunnel under the second mine of Kunyang Phosphate Mine, but also provide a reference for other mines under similar conditions. Through the application of these research results, we can effectively reduce the underground roadway safety problems caused by groundwater seepage and ensure the normal production of mines and the safety of workers. Not only do these observations provide a technical support for stability as well as improve the safety of production at the second mine at Kunyang Phosphate Mine, but also provide a reference for those in similar situations.

2. Experimental Overview

2.1. Materials

The concrete in this research was shotcrete mixed on site for supporting roadways in a mine, utilizing the polyformaldehyde (POM) fiber of Chongqing Yuntianhua. Polyformaldehyde is a polymeric material whose formula is expressed as (CH2O)n, where n is the number of repeating units of a chain of polymers of formaldehyde. The physical and mechanical properties of polyformaldehyde fibers include a tensile strength of approximately 150 MPa, a modulus of elasticity of about 3 GPa, and minimal absorption of water, which is an indication of its ability to resist dampness. Fibers of different lengths of 30 mm, 36 mm, and 42 mm (Figure 1), and corresponding dosages of fibers of 5 kg/m3, 7 kg/m3, and 9 kg/m3, respectively, were utilized in this study. The reference concrete was C20 grade shotcrete, which is extensively used in mining. In short, the materials used in this study have well-established properties that comply with the standard requirements of polyformaldehyde fibers and C20-grade shotcrete.

2.2. Test Scheme

In the second mine of Kunyang Phosphate Mine, the preparation of concrete samples of different proportions was carried out using the existing C20 shotcrete preparation equipment (Figure 2) and process flow of the mine (Figure 3). Through an experiment on the control variable design, two factors, and three levels, and according to the comprehensive experimental design method, a total of 10 experimental groups were designed, including 1 blank control group, and a total of 3 specimens were produced in each group. The experimental scheme design is shown in Table 1. The test specimens were of a conical shape, 175 mm in diameter at the upper end, 185 mm in diameter at the lower end, and 150 mm in height. The test specimens, after demolding for 24 h, underwent curing for 28 days. The test for concrete impermeability using the seepage height method and step pressure method of testing was conducted on an HP4.0-4 program-controlled impermeability meter. Figure 4 gives a broad idea of the test set-up of a testing machine, showing the test rig and its component units for studying the effect of polyformaldehyde fibers on concrete impermeability. The test set-up allows for well-controlled and repeat testing. The test rig was equipped with a number of test chambers for studying different testing samples in parallel, which allowed for controlled and uniform testing. The test procedure followed standard procedures given in ASTM C192 and ASTM C1116 for the testing of fibers in contents.

2.3. FEM Details

For the simulation of the stability of roadways built with polyformaldehyde fiber-strengthening concrete, FLAC3D, based on the Finite Element Method, was used to simulate the pore pressure in the groundwater. The groundwater and groundwater/surrounding rock interfaces were simulated using quadratic hexahedral elements. A mesh convergence study was conducted to confirm that the adopted mesh was valid. Meshes were systematically refined in high-gradient zones, such as in groundwater/surrounding rock contacts, to test for the numerical solution’s stability and accuracy. The result from this study confirmed that the solution stabilized with a mesh size of between 2 mm and 5 mm, and further refinement to a value of 1 mm had no significant effect on the solution’s accuracy. This verifies that the adopted mesh size generates stable and consistent results for numerical simulations.

2.4. Mixing Procedure

A standard process of the homogeneous distribution of polyformaldehyde fibers in the concrete batch was adopted. The cement, sand, and coarse aggregate were first dry-mixed in a forced-action blender for 1–2 min for uniform dispersive action. The polyformaldehyde fibers were then introduced in a controlled quantity for a period of 30–60 s in a low-speed blend, preventing the agglomeration of fibers. The measured water, in a predetermined quantity, was introduced for a period of 1–2 min, and the speed of mixing was ramped-up subsequently for the enhanced dispersive action of the fibers. The entire batch was then homogeneously blended in a high-speed operation for a time of 3–5 min for the complete integration of fibers, maintaining the homogeneity of the fibers and preventing their balling. The batch, after mixing, was examined for its homogeneity, and an additional 30 s of mixing, as required, followed. The resulting blend of concrete was then discharged and pumped for its instant utilization in supporting roadways. This sequential process prevented the agglomeration of fibers and ensured a uniform distribution of fibers, enhancing the concrete’s impermeability and mechanical properties.

3. Results and Analysis

3.1. Test Results and Analysis of Stepwise Pressure Method

The step-by-step pressure method was used to test the impermeability grade of concrete with different proportions [45]. The pressure gradually increased from 0.1 MPa and increased by 0.1 MPa every 8 h. The test results are shown in Table 2. Through the impermeability of different proportions of polyformaldehyde fiber concrete, it can be seen that the impermeability grade reached the P6 requirement [46]. Among them, the hydrostatic pressure of the first group (30 mm—5 kg/m3), the second group (30 mm—7 kg/m3), the fourth group (36 mm—5 kg/m3), and the seventh group (42 mm—5 kg/m3) reached 0.8 MPa, which was 0.1 MPa higher than that of the blank control group (without adding the fiber). It can be concluded that a small amount of polyformaldehyde fiber can improve the impermeability of concrete, but with a further increase in the polyformaldehyde fiber content, the impermeability of concrete begins to decrease [47,48].

3.2. Test Results and Analysis of Seepage Height Method

3.2.1. Analysis of Influence of Fiber Length on Impermeability of Concrete

The average value of the maximum value of the test specimen under the same water pressure condition was taken as the final result.
According to the test results in Figure 5, according to the impermeability of different lengths of polyformaldehyde fibers on concrete, it can be seen that the height of water seepage in the blank control group was 48 mm, and the height of water seepage first decreased and then increased with the increase in fiber length. In the case of the same fiber contents, when the fiber length was 30 mm, the permeability height of polyformaldehyde fiber concrete was reduced to the lowest, showing the best anti-permeability effect.

3.2.2. Analysis of Influence of Fiber Content on Impermeability of Concrete

As shown in Figure 6, under the same fiber length, when the dosage of polyformaldehyde fiber was 5 kg/m3, the concrete exhibited the best impermeability compared with when the dosage was 7 kg/m3 and 9 kg/m3. When the fiber content is low, the polyformaldehyde fiber can achieve better dispersion effects in concrete and construct an effective three-dimensional network structure. This structure effectively blocks the cracks and pores inside the concrete, significantly improves the compactness of the concrete, and then enhances its impermeability.

3.3. Analysis of Percolation Mechanism of Polyformaldehyde Fiber Concrete

3.3.1. Interaction Between Fiber Surface and Concrete

The interior of concrete contains a large number of pores, cracks, and tiny micro-cracks. A micromorphology diagram of polyformaldehyde fiber and concrete is shown in Figure 7. Polyformaldehyde fiber dispersed uniformly in concrete can form a good bonding effect with it, which enhances the elastic modulus of the concrete. Compared with ordinary concrete, the tensile strength of polyformaldehyde fiber concrete is enhanced, and the pores, cracks, and micro-cracks generated in the initial hardening of the concrete are inhibited. The addition of polyformaldehyde fiber significantly improves the compactness of concrete, effectively blocks the formation of many cracks and pores in the concrete, reduces the porosity of the concrete, and increases the density of the concrete. The mixture of the fiber and concrete makes the polyformaldehyde fiber and concrete form a dense whole and improves the cohesion within the concrete. When subjected to external stress, concrete can transfer stress through fiber, thereby inhibiting the formation and development of the concrete’s cracks, avoiding stress concentration, and improving the stability of the concrete. As shown in Figure 8, a three-dimensional network structure can be formed when the polyformaldehyde fibers fill the pores or cracks of concrete, and under the three-dimensional network structure, the polyformaldehyde fibers can effectively inhibit the development of pores or cracks.

3.3.2. Analysis of Influence Mechanism of Percolation of Polyformaldehyde Fiber Concrete with Different Lengths and Dosages

Polyformaldehyde fiber is uniformly dispersed in concrete and can form a good bonding effect with it, enhancing the elastic modulus of the concrete, and the polyformaldehyde fiber enhances the tensile strength of the concrete, inhibits the cracks generated and expanded in the initial hardening of the concrete, significantly improves the compactness of the concrete, and effectively blocks the formation of numerous cracks and pores inside the concrete [22,23,49,50]. In addition, the internal porosity of the concrete is reduced, and the difficulty of water migration in the concrete is increased, which effectively improves the impermeability of the polyformaldehyde fiber concrete [51]. However, with the increase in the length of the polyformaldehyde fiber, its dispersion uniformity in the concrete gradually becomes worse, and it becomes more prone to an aggregation phenomenon, which will not only form additional voids, as shown in Figure 9, but also likely cause these voids to be connected to each other, which will reduce the impermeability of the concrete. Therefore, the selection of an appropriate fiber length can ensure that the concrete has excellent impermeability [52].
With the further increase in the content of polyformaldehyde fiber, the seepage height inside the concrete also increases obviously, which indicates that its impermeability also decreases with the increase in the content. This is mainly due to the fact that a large number of polyformaldehyde fibers are incorporated into the concrete to form entanglement, clumping, etc., which affects the combination of polyformaldehyde fibers and concrete, resulting in the reduction of the concrete’s fluidity and the formation of new cracks and voids in the concrete, thus weakening the permeability of the concrete [53]. Therefore, reasonable control of the content of polyformaldehyde fiber can maintain or improve the impermeability of concrete.

4. Numerical Simulation Analysis Based on FLAC3D

4.1. Stratigraphic Lithology

The second mining area of Kunyang Phosphate Mine is located in the south west of Dianchi phosphorus accumulation area, adjacent to Kunyang Phosphate Mine’s Mining Areas 1 to 4 in the east, receiving Yunsi phosphate mine’s area in the west and Haikou phosphate mine in the north. It is located in Erjie Town, Jinning County, with a length of 4.50 km from east to west and a width of 1.70 km from north to south, and it has an area of 7.66 square kilometers. As one of the important large and medium-sized phosphate mines under Yunnan Phosphating Group Co., LTD., Kunyang Phosphate Mine No. 2 not only has rich experience in open-pit mining, but also has begun to transform into the construction stage of underground mining since 2020. The mining method of Kunyang Phosphate Mine No. 2 is a combination of open pit and underground. In order to ensure the safety and stability of the mining process, the filling mining method is adopted in the underground mine, and a safety pillar with a height of 20 m is retained at the junction between the open pit and the underground area.
The strata in the second mining area of Kunyang Phosphorus Mine (Table 3), from the oldest to the newest, include the Lower Cambrian Yuhucun Formation (Є1y), Zhongyicun Formation (Є1z), Qiongzhusi Formation (Є1q), Canglangpu Formation (Є1c), Middle Devonian Haikou Formation (D2h), Upper Zige Formation (D3z), Lower Carboniferous Datang Formation (C1d), Middle Weining Formation (C2w), and Lower Permian Stone Group (P1d) and fourth series (Q).

4.2. Hydrogeological Condition

The mining area is located in the recharge runoff area of Erjie River Basin. The lowest erosion base level in the hydrogeological unit is 1880 m, and the minimum design mining elevation is 1800 m. Some orebodies are located below the local minimum erosion base level. The directly water-filled aquifer of the orebody is the karst fissure aquifer of the Cambrian and Sinian systems, with an uneven distribution of water rich in space and a vertical trend of weakness going upward and high strength going downward. As the main water-filled aquifer of the ore body, only the Erjiehe Valley (flood plain and terrace) in the mining area distributes a Quaternary system, weakly containing pore water, and groundwater is mainly charged by atmospheric precipitation, so the Quaternary system’s pore water recharge is limited. In the later mining process, the method of dewatering and drainage is mainly adopted to ensure safe mining at the mine. The mining method adopts the pan-type pseudo-inclined sublevel strip-filling mining method, which has a low possibility of collapse. Therefore, the second Kunyang Phosphate Mine belongs to the karst fracture ore-bearing layer, and the floor is directly filled with water with moderate hydrogeological conditions.
The main source of groundwater recharge in the mining area is surface atmospheric precipitation. The average rainfall in the area from January 1974 to December 2019 was 873.3 mm, the maximum annual rainfall is 1144.1 mm (1994), and the maximum daily rainfall is 123.6 mm. The rainfall is mainly concentrated in May to October every year. It accounts for 85.3% of the annual rainfall. The exploitation of opencast mining areas directly exposes aquifers, thus affecting the recharge and flow of groundwater. After rainfall infiltration, the water table in these areas rises, increasing the amount of groundwater recharge. The hydrogeological conditions of the mining area are dominated by the fissure water filling in the strata and its roof and floor, and the complexity is of medium type. With the increase in the mining depth, the hydrogeological conditions tend to become complicated.

4.3. Model Building

This time, the 1980 m return air roadway in the second mine of Kunyang Phosphate Mine was selected for numerical simulation analysis. The roadway dimensions were as follows: width, 4.5 m; wall height, 2.5 m; three-core arch section. The supporting method was shotcrete support with a thickness of 100 mm, and the supporting method was partially shotcrete net support with a thickness of 150 mm. Regarding the cement strength, the strength grade of the shotcrete was C20. Based on the experimental data, the optimal ratio of polyformaldehyde fiber concrete (30 mm, 5 kg/m3) with the best impermeability was selected for the numerical simulation. The model size was 300 m × 300 m × 300 m, and the Mohr–Coulomb constitutive model was adopted. The horizontal displacement of the x axis and y axis boundary and the vertical displacement of the z axis boundary were fixed. According to the mine data and the field situation, the data obtained from the geological borehole ZK60-9 of the mine were modeled. The thickness of the model was appropriately increased above and below the top and bottom plates to reduce the boundary effect. The stratigraphic arrangement adopted by the model and its rock mechanics parameters are shown in Table 4, and the numerical model established is shown in Figure 10.

4.4. Analysis of Seepage Influence of Roadway Under Ordinary Support Conditions

Figure 11 shows a pore-water pressure diagram of the roadway. With the completion of the excavation and support work of the roadway, the groundwater began to penetrate into the roadway due to the water pressure difference around the roadway and gradually formed a seepage field centered around the roadway. In this funnel-shaped seepage field, groundwater flows along the movement track of cracks and rock layers to the center, forming an obvious seepage area around the roadway, with the pore water pressure reaching 1.7 MPa.
As can be seen in Figure 12 and Figure 13, due to the influence of groundwater seepage, the stress in the rock mass formed a stress concentration at the roof position of the roadway, resulting in the deformation of the roof. The maximum principal stress was 0.49 MPa, and the displacement was 43 mm. Under the action of stress, the stability of the roadway’s surrounding rock decreased significantly. The existence of pore pressure has an adverse effect on the stability of a roadway, and it changes the stress distribution around the roadway, resulting in a more serious stress concentration around the roadway, which affects the stability of the roadway [54,55]. This stress concentration may aggravate the deformation and failure of the surrounding rock, thus affecting the overall stability of the roadway. The roadway needs to be reinforced. The roadway should be strengthened to prevent and drain the water in time.

4.5. Analysis of Seepage Effect of the Roadway Under the Condition of a Polyformaldehyde Fiber Concrete Support

From Figure 14, Figure 15 and Figure 16, it can be clearly seen that for the polyformaldehyde fiber concrete support, the pore water pressure in the road was enhanced to 2.52 MPa, compared to the normal support. This shows a significant increase in the road’s capacity to resist the seepage of water. The deformation of the roof was minimized under this support, which was a displacement of 12.5 mm, a reduction of 30.5 mm compared to the normal support.
Furthermore, the maximum principal stress formed a stress concentration on the roadbed’s rooftop, which was a maximum of 0.91 MPa, 0.42 MPa higher compared to the normal support. These results illustrate that polyformaldehyde fiber concrete support can increase a roadbed’s permeability resistance and a roadbed’s stability, which can lower underground roadbed safety risks due to the seepage of groundwater. This can play a critical part in maintaining a tunnel’s stability and safety in groundwater-affected areas for a lengthy period.

5. Conclusions

This study investigated the enhancement of concrete impermeability using polyformaldehyde (POM) fibers for enhanced underground road stability and durability in seepage-condition underground road environments. The contribution of this study is in employing polyformaldehyde fiber concrete for enhanced road stability and seepage resistance in underground mining environments under the seepage of groundwater, an under-researched issue in mining engineering. In comparison to other conventional fibers, polyformaldehyde fibers have a great tensile capacity, alkalinity, and water-spreading capability, which have a great potential for concrete in resisting the seepage of water.
The following key results were attained:
  • Polyformaldehyde Fiber Concrete Improves Impermeability: The results of the test showed that a small amount of POM fibers can significantly enhance concrete impermeability. The best result was achieved when using a content amount of 5 kg/m3 of fibers of a size of 30 mm, which reached a hydrostatic stress of 0.8 MPa, which was higher than that of the blank control group.
  • Favorable Length and Fiber Content: The test results showed that the 30 mm fibers of a 5 kg/m3 content had the shortest seepage height, which yielded maximum impermeability. A fiber content amount of more than 7 kg/m3 showed a drop in impermeability due to a lack of fiber dispersion and an increase in porosity.
  • Numerical Simulation Calibration: FLAC3D numerical simulation confirmed that polyformaldehyde fiber concrete improves road stability by reducing displacement under seepage. The polyformaldehyde fiber blend showed improved resistivity compared to normal concrete support systems.
  • Effect on Roadway Stability due to Groundwater Seepage: In seepage, there was a minimal road displacement of polyformaldehyde fiber concrete, which was 30.5 mm lower, and improved pore water pressure resistance, which showed its potential in roadway stability in groundwater-saturated environments.
  • The best content amount of polyformaldehyde fibers for concrete is 5 kg/m3. This content level is a balance between realizing improved impermeability and maintaining an effective dispersion of fibers in a concrete matrix. Adding a higher content of fibers results in lower performance due to the aggregation of fibers and increased porosity. In conclusion, the use of polyformaldehyde fibers in concrete presents a promising solution for improving the impermeability and stability of underground roadways, especially in mining environments where groundwater seepage is a significant concern. This research contributes to the advancement of concrete technology, offering valuable insights into the application of polyformaldehyde fibers for durable, water-resistant construction materials.
Overall, polyformaldehyde fibers’ application in concrete is a viable alternative to improving stability as well as impermeability in underground roads, especially in mining regions with high groundwater seepage. The research contributes towards improving concrete technology by giving thoughtful insights into polyformaldehyde fibers’ application in manufacturing water-resistant construction materials that are durable. The research is innovative because it examines polyformaldehyde fibers as a specialized application in improving stability as well as impermeability in underground mining regions, which is a research field that has not been extensively researched.

Author Contributions

Investigation, Y.S. and G.W.; Resources, G.W. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the key project of the science and technology plan of the Science and Technology Department of Yunnan Province (202401AS070071), the Central Guidance of Local Science and Technology Development Fund (202407AC110019), and the Yunnan Fundamental Research Projects (grant NO. 202501AU070145).

Data Availability Statement

All data generated or analysed during this study are included in this published article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Polyoxymethylene fiber.
Figure 1. Polyoxymethylene fiber.
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Figure 2. Polyformaldehyde fiber concrete mixing process.
Figure 2. Polyformaldehyde fiber concrete mixing process.
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Figure 3. Shotcrete test sample.
Figure 3. Shotcrete test sample.
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Figure 4. Programmed impermeable meter host.
Figure 4. Programmed impermeable meter host.
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Figure 5. Water seepage height of specimens with different fiber lengths.
Figure 5. Water seepage height of specimens with different fiber lengths.
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Figure 6. Water seepage height of different fiber mixing specimens.
Figure 6. Water seepage height of different fiber mixing specimens.
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Figure 7. Polyformaldehyde fiber in concrete (Scale: 1 mm).
Figure 7. Polyformaldehyde fiber in concrete (Scale: 1 mm).
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Figure 8. Polyformaldehyde fiber’s reticular structure (scale: 50 µm).
Figure 8. Polyformaldehyde fiber’s reticular structure (scale: 50 µm).
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Figure 9. Polyformaldehyde fiber concrete and pore microstructure (scale: 10 mm).
Figure 9. Polyformaldehyde fiber concrete and pore microstructure (scale: 10 mm).
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Figure 10. Numerical model of roadway.
Figure 10. Numerical model of roadway.
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Figure 11. Pore water pressure of the surrounding rock of the roadway, with pressure values in Pascal (Pa) as indicated by the color scale on the left.
Figure 11. Pore water pressure of the surrounding rock of the roadway, with pressure values in Pascal (Pa) as indicated by the color scale on the left.
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Figure 12. Minimum principal stress of the roadway’s surrounding rock, with stress values in Pascal (Pa) as indicated by the color scale on the left.
Figure 12. Minimum principal stress of the roadway’s surrounding rock, with stress values in Pascal (Pa) as indicated by the color scale on the left.
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Figure 13. Displacement of the roadway’s surrounding rock under ordinary support conditions, with displacement values in meters (m) as indicated by the color scale on the left.
Figure 13. Displacement of the roadway’s surrounding rock under ordinary support conditions, with displacement values in meters (m) as indicated by the color scale on the left.
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Figure 14. Pore water pressure under polyformaldehyde fiber concrete supporting conditions, with pressure values in Pascal (Pa) or MegaPascal (MPa) as indicated by the color scale on the left.
Figure 14. Pore water pressure under polyformaldehyde fiber concrete supporting conditions, with pressure values in Pascal (Pa) or MegaPascal (MPa) as indicated by the color scale on the left.
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Figure 15. Minimum principal stress under polyformaldehyde fiber concrete supporting conditions, with stress values in Pascal (Pa) as indicated by the color scale on the left.
Figure 15. Minimum principal stress under polyformaldehyde fiber concrete supporting conditions, with stress values in Pascal (Pa) as indicated by the color scale on the left.
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Figure 16. Displacement of the roadway’s surrounding rock under a polyformaldehyde fiber concrete support, with displacement values in meters (m) as indicated by the color scale on the left.
Figure 16. Displacement of the roadway’s surrounding rock under a polyformaldehyde fiber concrete support, with displacement values in meters (m) as indicated by the color scale on the left.
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Table 1. Test scheme of polyformaldehyde fiber concrete.
Table 1. Test scheme of polyformaldehyde fiber concrete.
NumberFiber TypePOM Fiber Length (mm)POM Fiber Content (kg/m3)Fiber Manufacturer
1Polyformaldehyde305Yuntianhua Co., Ltd., Chongqing, China
2Polyformaldehyde307Yuntianhua Co., Ltd., Chongqing, China
3Polyformaldehyde309Yuntianhua Co., Ltd., Chongqing, China
4Polyformaldehyde365Yuntianhua Co., Ltd., Chongqing, China
5Polyformaldehyde367Yuntianhua Co., Ltd., Chongqing, China
6Polyformaldehyde369Yuntianhua Co., Ltd., Chongqing, China
7Polyformaldehyde425Yuntianhua Co., Ltd., Chongqing, China
8Polyformaldehyde427Yuntianhua Co., Ltd., Chongqing, China
9Polyformaldehyde429Yuntianhua Co., Ltd., Chongqing, China
Blank control group-00-
Table 2. Test results of paraformaldehyde fiber concrete.
Table 2. Test results of paraformaldehyde fiber concrete.
NumberFiber RatioHydrostatic Pressure (MPa)
130 mm—5 kg/m30.8
230 mm—7 kg/m30.8
330 mm—9 kg/m30.7
436 mm—5 kg/m30.8
536 mm—7 kg/m30.7
636 mm—9 kg/m30.7
742 mm—5 kg/m30.8
842 mm—7 kg/m30.7
942 mm—9 kg/m30.7
Blank control group00.7
Table 3. Brief description of mining area formation.
Table 3. Brief description of mining area formation.
BoundarySystemSeriesGroupDesignationThickness (m)
Cenozoic erathemQuaternary system Q<20
Paleozoic erathem
Pt		Permian systemLower seriesTipping groupP1d3.5~16.5
Carboniferous systemMiddle seriesWeining formationC2w25~30
Lower seriesDatang formationC1d9~28
Devonian systemUpper seriesZage formationD3z40.41~153.52
Middle seriesHaikou formationD2h5.16~28.93
Cambrian systemLower seriesCanglangpu formationЄ1c10~66.89
Zhusi formationЄ1q121.72~272.45
Zhongyi Village formationЄ1z2.86~29.76
Yuhu Village formationЄ1y101~170
Algonkian
Pt		Sinian systemUpper seriesIntercept of isochronZ2dn200~270
Table 4. Rock mechanics parameters.
Table 4. Rock mechanics parameters.
RockThickness (m)Bulk Modulus (GPa)Shear Modulus (GPa)Tensile Strength (MPa)Cohesive Force (MPa)Angle of Internal Friction (°)
dolomite \21.436.621.32.3543.8
sandstone9.2814.046.111.61.0943.3
shale46.8113.338.003.34.3747.2
mudstone3.1711.317.792.62.3543.3
dolomitic siltstone8.0012.007.201.52.3843.9
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Sang, Y.; Wang, G. Study on Seepage Effect of Roadway Based on Polyformaldehyde (POM) Fiber Concrete. Appl. Sci. 2025, 15, 3503. https://doi.org/10.3390/app15073503

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Sang Y, Wang G. Study on Seepage Effect of Roadway Based on Polyformaldehyde (POM) Fiber Concrete. Applied Sciences. 2025; 15(7):3503. https://doi.org/10.3390/app15073503

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Sang, Yongshuai, and Guangjin Wang. 2025. "Study on Seepage Effect of Roadway Based on Polyformaldehyde (POM) Fiber Concrete" Applied Sciences 15, no. 7: 3503. https://doi.org/10.3390/app15073503

APA Style

Sang, Y., & Wang, G. (2025). Study on Seepage Effect of Roadway Based on Polyformaldehyde (POM) Fiber Concrete. Applied Sciences, 15(7), 3503. https://doi.org/10.3390/app15073503

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