Study on the Performance Evaluation Method and Application of Drainage Nonwoven Geotextile in the Yellow River Sediment Filling Reclamation Area

Abstract

Technical challenges associated with drainage and filling efficacy confront the Yellow River sediment filling reclamation, a novel approach to reclaiming coal-mined subsided lands. This study proposes an improved geotextile performance evaluation method to address the shortcomings of current geotextile screening methodologies in the drainage of the Yellow River sediment. This method comprehensively considers essential characteristics under working conditions, such as permeability, soil conservation, and blockage prevention properties, including indicators such as the permeability coefficient and sediment retention rate of geotextiles under pressure. Indoor flume filling and drainage experiments were implemented to verify the efficacy of geotextile drainage. The improved method identified thermal-bonded nonwoven geotextiles of 200 and 250 g·m⁻² as having the highest comprehensive evaluation scores. The experimental results showed that these geotextiles significantly improved their drainage efficiency and better met the specific requirements of the Yellow River sediment filling reclamation. Traditional screening methods may be unsuitable for sediment drainage conditions, necessitating sediment interception and rapid drainage due to the streaming water–sediment mixture. Therefore, the newly established performance evaluation method is more appropriate for the specific requirements. It is recommended that a simple vibrating device be installed to maintain 20 vibrations per minute to keep drainage channels clear and provide stable drainage performance in engineering applications.

1. Introduction

China’s main energy source is coal, but the country’s land resources, particularly arable land, are seriously threatened by coal extraction, which has caused substantial land subsidence. This makes critically low amounts of arable land resources more scarce per person [1,2,3]. Statistical estimates indicate that approximately 13.33 million hectares of arable land nationwide is threatened by coal mining subsidence [4]. To date, coal mining has caused the subsidence of 1.8 million hectares of land, with an annual increase of 70,000 million hectares [5]. To effectively manage coal-mined subsided lands, fly ash and coal gangue fill the voids, restoring the surface topography and land functionality [6,7]. However, the limited availability and potential for contamination of these materials restrict their broader application [8,9,10]. In recent years, the use of Yellow River sediment for filling reclamation has emerged as a novel approach [11]. The fine, pollution-free sediment from the Yellow River main canal is particularly suitable for this purpose [12]. This method mitigates the issues of river channel blockage and land occupation by dredged sediment. It facilitates the reclamation of land damaged by coal mining along the Yellow River, achieving dual benefits [13,14,15]. Nonetheless, technical challenges persist. The water–sediment mixture used for filling must be dewatered before further reclamation processes can convert it into arable land [16], presenting a significant dewatering challenge [17]. Currently, drainage by excavating outlets in embankments at the end of reclamation strips leads to the loss of fine-grained sediment rich in nutrients with a high water retention capacity, resulting in a highly permeable fill layer with poor water and nutrient retention properties [18]. This also causes sedimentation in drainage channels. Additionally, the supersaturated water within the fill material, which is obstructed by the end embankments, can only drain vertically, resulting in low drainage efficiency and prolonged reclamation periods [10,16,17]. Therefore, there is an urgent need to develop new technological solutions to address sediment loss and drainage issues, enhance the efficiency of filling reclamation processes, and promote the large-scale application of Yellow River sediment reclamation technology.

Geotextiles, known for their high strength, excellent flexibility, and superior overall performance, play a pivotal role in various engineering domains, particularly in transportation infrastructure, hydraulic engineering, riverbank protection, and saline–alkali subsurface drainage systems. Their primary functions include filtration, drainage, separation, reinforcement, and protection [19,20]. Common types of geotextiles include nonwoven and woven geotextiles. Nonwoven geotextiles are widely utilized in various drainage systems because of their exceptional filtration, permeability properties, and relatively low cost. Research by [21] demonstrates that geotextiles effectively reduce the turbidity of drainage water when used as a filtration layer. Similarly, ref. [22] conducted large-scale flume experiments to evaluate the efficacy of different nonwoven geotextiles in erosion control and sediment interception, showing that geotextiles significantly decrease the sediment concentration in the drainage water, often exceeding the expected performance. According to the “Technical Code for Application of Geosynthetics” [23], the geotextiles used in hydraulic engineering must satisfy three fundamental requirements: soil conservation, permeability, and blockage prevention. Soil conservation is closely related to the equivalent opening size (O₉₀) of the geotextile, which should be smaller than the particle size that forms the skeleton of the protected soil, yet large enough to allow fine particles to pass through smoothly. Studies indicate that the O₉₅ of geotextiles should be less than the characteristic particle size (d₈₅) of the protected soil, adjusted by a particle gradation coefficient [24]. In terms of permeability, the permeability coefficient (k_g) of the geotextile should be greater than that of the protected soil (k_s) when the soil has good particle gradation (such as clean sand and medium-coarse sand), a low hydraulic gradient, and a low likelihood of clogging. When the permeability coefficient of the geotextile is more than ten times greater than that of the surrounding soil, it effectively reduces drainage resistance [24]. Therefore, to prevent drainage failure that could lead to structural damage, high repair costs, and complex flow conditions under high hydraulic gradients, the permeability of the geotextile coefficient (k_g) should generally be greater than ten times the permeability coefficient of the soil (10 k_s). Blockage prevention performance is assessed through gradient ratio (GR) filtration tests, which calculate the hydraulic gradient by measuring the head loss across different points within the geotextile–soil system. The GR value is the ratio of unit head loss in a geotextile–soil system (25 mm thick soil layer plus geotextile) to that in a geotextile-only layer (50 mm thick). To ensure good blockage prevention properties, the GR should be less than 3, a standard incorporated into geotextile filtration design requirements [25].

Research has indicated that needle-punched nonwoven geotextiles with specifications of 250 and 300 g·m⁻² can partially intercept fine particles in sediment during the reclamation of coal-mined subsided lands along the Yellow River, and they exhibit a certain efficacy in lateral drainage [10]. However, practical engineering applications have revealed clogging issues with selected nonwoven geotextiles, leading to sediment interception and drainage failure. Current geotextile selection for engineering purposes is based on a comparative analysis of soil conservation, permeability, and blockage prevention properties [23]. Specifically, the geotextile’s equivalent opening size (O₉₀) should be able to intercept soil particles with a diameter that is 90% of the target particle size, meaning that the O₉₀/d₉₀ value must exceed 1 [24]. Additionally, the permeability coefficient of the geotextile should be more than ten times greater than that of the intercepted soil [24], with a gradient ratio below 3 [25]. In practice, the permeability coefficient of the geotextile dramatically decreases under the influence of hydraulic and soil pressures [26], leading to clogging upon sediment retention [27]. This finding underscores the critical importance of the blockage prevention performance of the geotextile as the effective opening area decreases [19]. Therefore, in the selection process of geotextiles, besides the fundamental criteria of soil conservation, permeability, and blockage prevention properties, it is imperative to consider specific operational conditions, including lateral pressure and sediment retention during dynamic water drainage.

Given the severe clogging issues encountered in the practical application of geotextiles for drainage, there is an urgent need to identify suitable types of geotextiles and determine appropriate engineering application methods. This study aims to develop a scientific evaluation model to screen suitable geotextiles and conduct indoor flume drainage tests to validate the model’s scientific robustness and applicability. The main components of this research are as follows: (1) By considering the fundamental properties of soil conservation, permeability, and blockage prevention capability, along with the sediment retention rate and the permeability coefficient of geotextiles under pressure, a performance evaluation model for drainage geotextiles in the Yellow River sediment filling reclamation area was established. (2) The performance of the drainage geotextiles was validated through indoor flume drainage tests, and the optimal engineering application method was identified.

2. Materials and Methods

2.1. Experimental Materials

2.1.1. Geotextiles

Two types of geotextiles with consistent outer fibers but different manufacturing processes were selected, comprising eight variations (

Table 1. Geotextile gross weight and drainage performance parameters.

Experiment	Gross Weight	${\mathit{k}}_{\mathbf{n}}$	${∆\mathit{k}}_{\mathbf{n}}^{20}$	AOS	GR	${\mathit{T}}_{\mathbf{p}}$
	g × m−2	cm × s−1	cm × s−1	mm	-	%
N1	300	9.95 × 10−2	5.98 × 10−2	1.00 × 10−1	9.92	9.92
N2	200	4.62 × 10−2	2.78 × 10−2	1.03 × 10−1	10.67	10.67
T1	300	5.30 × 10−2	9.00 × 10−4	1.23 × 10−1	4.64	4.64
T2	250	5.07 × 10−2	9.00 × 10−4	1.33 × 10−1	4.42	4.42
T3	200	4.65 × 10−2	8.00 × 10−4	1.47 × 10−1	4.07	4.07
T4	160	3.07 × 10−2	5.00 × 10−4	1.52 × 10−1	2.68	2.68
T5	120	2.94 × 10−2	5.00 × 10−4	1.63 × 10−1	3.03	3.03
T6	100	2.72 × 10−2	5.00 × 10−4	1.74 × 10−1	2.63	2.63

Notes: N1, N2 are needle-punched nonwoven geotextiles; T1~T6 are thermal-bonded nonwoven geotextiles; k_n is permeability coefficient (STM D 5493) [28]; ${∆k}_{\mathrm{n}}^{20}$ is change in permeability coefficient at 20 kPa with reference [29]; AOS is the apparent opening size (ASTM D 4751) [30]; GR is gradient ratio (ASTM D 5101-01) [31]; T_p is sediment retention rate with reference [32].

). The first type is a needle-punched nonwoven geotextile made of polyester fibers, with specifications including 200 and 300 gžm⁻² short-fiber needle-punched nonwoven geotextile (Jinan Mingfeng Engineering Materials Co., Ltd., Jinan, China). The second type is a thermal-bonded nonwoven geotextile, composed of polyester fiber-wrapped nylon, with specifications ranging from 100 to 300 gžm⁻² of Colback thermal-bonded nonwoven geotextile (Freudenberg Performance Materials (Changzhou) Co., Ltd., Changzhou, China). The basic parameters, such as weight and drainage performance parameters, are detailed in the table below.

2.1.2. The Yellow River Sediment

The Yellow River sediment dredged by the sediment dredging ship from the Yellow River main canal in Dezhou city, Jining County, Shandong Province (Figure 1a–c), was transported through a pipeline and filled over 3000 acres of coal-mined subsided land at a concentration of 200~300 kgžm⁻³ [16,17]. The sediment utilized in this study was extracted from the Yellow River Jijin Main Canal by a sediment dredging ship and underwent purification to remove impurities before being used as an experimental material. To replicate the actual filling conditions as closely as possible, experimental water with a pH of 7.64 and conductivity of 696 µS·cm⁻¹ was employed to mimic the field conditions closely. The particle size distribution, uniformity coefficient (C_u), and curvature coefficient (C_c) of the sediment extracted by the sediment dredging ship from the Yellow River Jijin Main Canal are as follows (Figure 1d).

2.2. Geotextiles Performance Evaluation Method

This study adheres to the requirements for permeability, soil conservation, and blockage prevention capabilities of geotextiles for hydraulic engineering as outlined in the “Technical Specification for Application of Geosynthetics” [23]. Specifically, a comprehensive method to evaluate the performance of geotextiles under the unique conditions of the Yellow River sediment filling reclamation drainage is proposed. The method is as follows:

(1)

Construction of the evaluation index system: Based on the three fundamental criteria of permeability, soil conservation, and blockage prevention capability, a multilevel evaluation index system was established (Table 2).

(2)

Normalization of indicators: Data standardization was performed to eliminate dimensional differences among various indicators. The raw indicator values were converted into dimensionless values via a standardization formula (Equation (1)).

(3)

Determination of indicator weights: The entropy weight method was employed to objectively determine the weights of each indicator based on the amount of information in the data (Equations (2)–(4)).

(4)

Calculation of comprehensive scores: By combining the weights obtained from the entropy weight method, the comprehensive performance scores for each type of geotextile were calculated (Equation (5)). The geotextiles were then ranked based on these scores, with an average of five degrees from 0 to 1. A higher score indicates better overall performance, making the geotextile more suitable for the Yellow River sediment filling reclamation drainage projects.

This systematic approach ensures that the selected geotextiles meet the specific demands of the application, providing a reliable and effective solution for the drainage issues associated with sediment filling reclamation.

$${x^{\prime }}_{ij}=\left\{\begin{array}{c}{\displaystyle \frac{x_{ij}}{max\left(x_{ij}\right)}} Positive indicator \\ {\displaystyle \frac{min\left(\left|x_{ij}-a\right|\right)}{\left|x_{ij}-a\right|}} Intermediate indicator\\ {\displaystyle \frac{min\left(x_{ij}\right)}{x_{ij}}} Negative indicator\end{array}\right.$$

(1)

$$p_{ij}={\displaystyle \frac{{x^{\prime }}_{ij}}{\sum _{i=1}^m {x^{\prime }}_{ij}}}$$

(2)

$$e_j=-{\displaystyle \frac{1}{\ln \left(m\right)}}\sum _{j=1}^m p_{ij}\ln \left(p_{ij}\right)$$

(3)

$$w_j={\displaystyle \frac{1-e_j}{n-\sum _{j=1}^n e_j}}$$

(4)

$${\gamma }_i=\sum _{j=1}^n w_j{x^{\prime }}_{ij}$$

(5)

where $x_{ij}$ denotes the original value of the j indicator of the i geotextile under consideration, where j = 1, 2, …, n, with n representing the total number of evaluation indicators, specifically n = 5. When j takes the values of 1, 2, 3, 4, and 5, they correspond to the permeability coefficient, the change in permeability coefficient of the geotextile under maximum vertical pressure during the drainage process, the equivalent pore size, the gradient ratio, and the sediment retention rate, respectively. Additionally, i = 1, 2, …, m, and m signifies the total number of geotextile types under evaluation. ${x^{\prime }}_{ij}$ denotes the normalized result of the original value of the j indicator of the i geotextile; a is the reference value, which can be taken as the sediment characteristic particle size $d_{85}$, representing the cumulative particle size of 85% in the sediment particle size distribution curve; $p_{ij}$ signifies the probability of the normalized result of the j indicator of the i geotextile; $e_j$ indicates the entropy value corresponding to the j indicator; $w_j$ corresponds to the weight of the j indicator; and ${\gamma }_i$ is the comprehensive score of the i geotextile, ranging from 0 to 1, which is divided into five grades, with higher scores indicating the superior overall performance of the geotextile.

Table 2. Evaluation index system and index properties.

Criterion Layer	Indicator Layer	Properties
Permeability	Permeability coefficient ($k_{\mathrm{n}})$	Positive
	Change of $k_{\mathrm{n}}$ at 20 kPa (${\Delta k}_{\mathrm{n}}^{20})$	Negative
Soil conservation	Apparent opening size (AOS)	Intermediate
Blockage prevention	Gradient ratio (GR)	Negative
	Sediment retention rate ($T_{\mathrm{p}})$	Negative

Table 2. Evaluation index system and index properties.

Criterion Layer	Indicator Layer	Properties
Permeability	Permeability coefficient ($k_{\mathrm{n}})$	Positive
	Change of $k_{\mathrm{n}}$ at 20 kPa (${\Delta k}_{\mathrm{n}}^{20})$	Negative
Soil conservation	Apparent opening size (AOS)	Intermediate
Blockage prevention	Gradient ratio (GR)	Negative
	Sediment retention rate ($T_{\mathrm{p}})$	Negative

2.3. Indoor Flume Filing and Drainage Experiment

This study used an indoor polypropylene (PP) plastic flume (Figure 2a). The dimensions of the PP plastic flume used for the experiment were 120 × 60 × 80 cm (length × width × height). Three treatments were established: T2 (full drainage cross-section opening + thermal-bonded nonwoven geotextile of 250 g·m⁻²), T3 (full drainage cross-section opening + thermal-bonded nonwoven geotextile of 200 g·m⁻²), and CK (partial drainage cross-section opening with an adjustable height plastic board). First, Yellow River sediment was prepared and air-dried to ensure a constant moisture content. The geotextiles to be tested were cut to the appropriate size and secured onto the PP plastic frame at the drainage cross-section as the geotextile treatment (Figure 2b). The CK treatment used foam boards to block the drainage outlet for height adjustment (Figure 2c). The PP plastic flumes were then sequentially arranged, and a sludge pump was used to fill them with a water–sand mixture at a concentration of 200 kg·m⁻³ until the flume was level. The geotextile-treated flumes drained through the side of the geotextile, whereas the CK treatment adjusted the drainage using the height-adjustable plastic board. After the water–sand mixture fully flowed in, additional mixtures were added periodically until the sediment accumulated to the predetermined height of 30 cm.

During the experiment, drainage samples were collected in six beakers for each treatment after a stable drainage period of 10 min and again 10 min before the filling process ended. The sediment concentration in the drainage was measured using an HACH sludge concentration meter. During the drainage period, a 1 kg mallet was used to strike the geotextile at frequencies of 0, 10, 20, and 30 times per minute with an amplitude of 20 mm. Additionally, the drainage flow rate was calculated by collecting and weighing the volume of water drained in one minute using a graduated cylinder at these tapping frequencies. Once the filling was complete and clear water was drained, METER EC-5 soil moisture probes were inserted at the positions 1, 2, and 3 (15, 60, and 105 cm from the drainage outlet) at the surface (0–15 cm) and bottom (15–30 cm) layers to record the sediment moisture content. Moisture content readings were recorded every hour.

2.4. Statistical Analysis

To more accurately reflect the drainage effectiveness of the geotextile and eliminate the impact of external factors such as temperature evaporation and sediment on the changes in sediment moisture content, a dimensionless effective drainage rate (EDR) index was developed. The EDR is calculated according to the following formula (Equation (6)):

$$EDR={\displaystyle \frac{{\theta }_{imax}-{\theta }_{ij}}{{\theta }_{ckmax}-{\theta }_{ckj}}}$$

(6)

where $EDR$ is the drainage efficiency ratio, dimensionless; ${\theta }_{imax}$ is the maximum moisture content of the class i geotextile water flume test, %; ${\theta }_{ij}$ is the class i geotextile j moment water flume experimental maximum moisture content, %; ${\theta }_{ckmax}$ is the maximum moisture content of the control test flume experiment, %; and ${\theta }_{ckj}$ is the j momentary control test flume experimental moisture content, %.

For the implementation of one-way ANOVA, Origin 2021 graphic and data analysis software (Origin Lab, Newton, MA, USA) can be used for analysis and visualization. The level of statistical significance was set at p < 0.05.

3. Results

3.1. Evaluation of Geotextile Drainage Performance

Based on the constructed evaluation index system and employing the entropy weight method to determine the weights of each indicator objectively (Figure 3a), the weight ranking is as follows: ${\Delta k}_{\mathrm{n}}^{20}$ > AOS > $T_{\mathrm{p}}$ > $k_{\mathrm{n}}$ > GR. This finding indicates that, among the preliminarily selected geotextiles, the change in $k_{\mathrm{n}}$ at 20 kPa and the apparent opening size (AOS) exhibit the most significant variation, thereby holding greater importance in the evaluation. In contrast, the relative significance of $T_{\mathrm{p}}$, $k_{\mathrm{n}}$, and GR is lower, aligning with the specific working conditions of Yellow River sediment filling and drainage.

The evaluation results (Figure 3b) revealed noticeable differences in the scores of various treatments across different indicators. Overall, the thermal-bonded nonwoven geotextiles consistently scored higher on multiple indicators than the needle-punched nonwoven geotextiles. Specifically, the evaluation scores for the thermal-bonded geotextiles (T1–T6) are 0.67, 0.87, 0.87, 0.76, 0.65, and 0.64, respectively, indicating their greater suitability for the Yellow River sediment filling reclamation and drainage conditions. Among these, the T2 and T3 (250 and 200 g·m⁻²) thermal-bonded geotextiles performed the best. Conversely, the evaluation scores for needle-punched nonwoven geotextiles were generally lower, with N1 scoring 0.25 and N2 scoring 0.18. This demonstrates that needle-punched nonwoven geotextiles are not entirely suitable for the conditions of Yellow River sediment filling reclamation and drainage.

In conclusion, through the analysis of the weight of each performance indicator of the geotextiles and the comprehensive score evaluation using the entropy weight method, it can be deduced that thermal-bonded nonwoven geotextiles, particularly the 250 g·m⁻² and 200 g·m⁻² specifications of the thermal-bonded geotextiles, exhibit better applicability in Yellow River sediment filling reclamation and drainage.

3.2. Indoor Flume Filing and Drainage

3.2.1. Sediment Content in Drainage Water

According to the evaluation results of the geotextiles (Figure 3), T2 (250 g·m⁻²) and T3 (200 g·m⁻²) are more suitable for the drainage conditions of Yellow River sediment filling reclamation. An indoor flume filling and drainage experiment was conducted to validate the drainage effectiveness of these geotextiles. The results (Figure 4) revealed that sediment loss during drainage exhibited a trend of being higher initially and decreasing over time. The T2 and T3 geotextiles exhibit a significantly lower sediment loss during both the initial and final stages of drainage compared to the control treatment (CK). This observation indicates that the control treatment (CK) features a narrower drainage cross-section and a wider channel, allowing suspended sediment particles to flow out over the weir with the water current. In contrast, the T2 and T3 geotextiles provide a wider drainage cross-section and a narrower channel, preventing suspended sediment particles from traversing the fine drainage pathways of the geotextiles, thereby reducing the sediment content in the drainage. This further confirms the effectiveness of the geotextiles under the specific conditions of the Yellow River sediment filling reclamation.

Specifically, compared with the control treatment (CK), the T2 geotextile treatment reduced the sediment content in the drainage water by an average of 62.45% in the early stage and 79.34% in the late stage, with an overall average reduction of 70.89%. The T3 geotextile treatment achieved an average decrease of 56.15% in the early stage and 70.53% in the late stage, with a total average reduction of 63.37%. These results indicate that the selected thermal-bonded nonwoven geotextiles of T2 and T3 perform the best, significantly reducing the sediment content in the drainage water. The data demonstrate that using the selected T2 and T3 geotextiles can markedly decrease the sediment content in drainage, with T3 showing slightly better performance than T2.

3.2.2. Moisture Content of Infill Sediment

For the surface sediment (0–15 cm), there were significant differences in moisture content among points 1, 2, and 3. Figure 5a–c illustrate that, for the T2 (250 g·m⁻²) and T3 (200 g·m⁻²) geotextile treatments, the surface sediment moisture content sharply decreased from approximately 35% to around 20% starting on the third day after filling. This was particularly notable at points 1 and 2, where the surface moisture content remained consistently lower than that of the CK treatment over the 37-day monitoring period, initially declining rapidly and then more gradually. This is due to the elevated moisture content within the sediment, resulting in a higher conductivity and a faster flow rate. As drainage progresses, the sediment gradually transitions into an unsaturated state, leading to a reduction in conductivity as the moisture content decreases, consequently causing the drainage rate to slow progressively. Conversely, in the CK treatment, due to the narrow drainage section of the overflow weir and the existence of a certain height between the weir and the bottom Yellow River sediment, the sediment moisture content steadily decreased from the completion of filling to the end of the experiment, and except for point 3 in the first three days, it was consistently higher than that in the geotextile treatments. Overall, the moisture content of the surface sediment in the T2 and T3 geotextile treatments was lower than that in the CK treatment throughout the experimental period, indicating that the selected geotextiles, which provided full-section side drainage with a wider drainage section and sufficient drainage channels for water to flow through, effectively accelerated lateral drainage from the surface sediment.

For the bottom sediment (15–30 cm), at point 1, the moisture content of the bottom sediment sharply decreased from approximately 35% to around 25%, starting on the third day after filling. It remained consistently lower than that in the CK treatment over the 37-day monitoring period, initially decreasing rapidly and gradually. Figure 5d–f show that the moisture content at point 2 decreased more slowly than at point 1 but faster than the CK treatment. At point 3, the moisture content of the bottom sediment was initially close to that in the CK treatment for the first three days after filling, then gradually decreased over time to below that of the CK treatment. Overall, the moisture content of the bottom sediment in the T2 and T3 geotextile treatments was lower than that of the CK treatment throughout the experimental period, indicating that the selected geotextiles effectively accelerated lateral drainage from the bottom sediment.

4. Discussion

4.1. Evaluation and Comparison of Basic Drainage Performance of Nonwoven Geotextiles

4.1.1. Enhancing the Efficacy of Evaluation Methods

When evaluating the performance of geotextiles, establishing appropriate standards is crucial. In hydraulic engineering, geotextiles often meet three fundamental requirements: permeability, soil conservation, and blockage prevention capabilities [23]. For the Yellow River sediment filling reclamation and drainage, the apparent opening size (AOS) of soil-retaining drainage geotextiles should be less than the particle size distribution coefficient BS, which is 0.158 mm in this case, to achieve optimal soil conservation [10]. The experimental results indicate that the AOS of geotextiles N1, N2, T1, T2, T3, and T4 are less than 0.158 mm, thus exhibiting good sediment interception and soil conservation capabilities. The analysis of the permeability coefficient (k_n) (Figure 6b), revealed that the permeability coefficients of the nonwoven geotextiles N1, N2, T1, T2, T3, T4, and T5 are more than ten times greater than the permeability coefficient of Yellow River sediment [24], ensuring adequate permeability. Long-term gradient ratio tests reveal that the GR values for geotextiles N1, N2, T1, T2, T3, T4, T5, and T6 are all less than 3 [25], theoretically satisfying the requirements of a filter layer and exhibiting an excellent blockage prevention performance. However, the selected needle-punched nonwoven geotextiles could not be quantitatively evaluated, and clogging was experienced during application [16].

Although these standards are scientifically reasonable, traditional methods for evaluating permeability and blockage prevention performance rely solely on permeability coefficient and gradient ratio, which have limitations in practical applications. For example, the permeability coefficient can significantly decrease under soil–water pressure [26], and geotextiles may easily clog when combined with clay particles [19,27,33]. Therefore, solely considering AOS, k_n, and GR may not comprehensively evaluate the performance of geotextiles under specific conditions. This indicates a partial perspective; preliminary screening can only qualitatively select geotextiles. On the other hand, the appropriate indicators should be chosen to represent different conditions. The evaluation method proposed in this study introduces new indicators, such as the change in the permeability coefficient under 20 kPa pressure [29] and the sediment retention rate [32]. It employs the entropy weight method to objectively determine each indicator’s weight, thus providing a more comprehensive and objective assessment of the geotextile performance. This improved evaluation method offers a more scientific and reliable basis for selecting geotextiles, enhancing their effectiveness in engineering applications.

4.1.2. Superiority of Drainage Performance

To comprehensively evaluate the drainage performance of geotextiles, this study proposes a novel assessment method and compares it with previous research [10] (Figure 6). Considering external factors such as evaporation due to test temperatures and sediment which affect sediment moisture content changes, we constructed a dimensionless effective drainage rate (EDR) for comparison. Overall, when the EDR of the CK treatment was used as a baseline (EDR = 1), most EDR values for the T2 and T3 treatments, as well as the ZW-300 (300 g·m⁻² needle-punched nonwoven geotextiles) and ZW-250 (200 g·m⁻² needle-punched nonwoven geotextiles) treatments at points 1, 2, and 3, both at the surface and bottom layers, exceeded 1. This finding indicates that geotextiles can accelerate drainage over extended periods.

From the perspective of surface sediment, the EDR values measured at points 1, 2, and 3 for the T2 and T3 treatments gradually decreased but remained higher than those for the ZW-300 and ZW-250 treatments. This suggests that sediment closer to the geotextile drainage outlet drains more rapidly, and the drainage efficacy of the T2 and T3 treatments surpasses that of ZW-300 and ZW-250. For bottom-layer sediment, the EDR values measured at points 1, 2, and 3 for T2 and T3 treatments initially increased but then decreased, remaining higher than those for the ZW-300 and ZW-250 treatments. This indicates that sediment closer to the geotextile drainage outlet drains more swiftly, with moisture from the surface sediment and terminal sediment also seeping downward to be expelled. Consequently, the drainage performance of the T2 and T3 treatments was superior to that of ZW-300 and ZW-250.

Additionally, in this study, we used a Hach moisture probe to record the sediment moisture content for T2 and T3 treatments in real-time, resulting in smoother EDR data. Conversely, for the ZW-300 and ZW-250 treatments, this study [10] employed a method of inserting the probe at scheduled times daily to record the sediment moisture content. This manual operation inevitably introduced some errors, leading to fluctuations in the EDR data.

4.2. Engineering Application Methods of Drainage Geotextiles

An analysis of the moisture content of the filled sediment revealed that the moisture content of the sediment treated with the T2 (250 g·m⁻²) and T3 (200 g·m⁻²) geotextiles was consistently lower than that of the sediment treated with the CK over the experimental period (Figure 5). This finding confirms the efficacy of the selected geotextiles in expediting lateral drainage. Drainage geotextiles function primarily by intercepting soil particles through perforated channels and facilitating water discharge. The presence of geotextiles inevitably reduces permeability, further declining as soil particles accumulate [26,34]. Research indicates that the permeability of geotextiles is initially high but decreases gradually with the accumulation of soil particles [35]. Therefore, maintaining initial permeability and continuous drainage is crucial for the Yellow River sediment filling reclamation [17]. During the experiment, vibrations were simulated by striking the geotextiles with a 1 kg mallet and an amplitude of 20 mm during the drainage process, aiming to stabilize the water permeability by eliminating the residue of soil particles. The results (Figure 7) showed that water discharged rapidly in the initial drainage phase, and after some time, the drainage rate stabilized at 15–20 g·s⁻¹. For the T2 and T3 treatments, as the vibration frequency increased, the channels in the geotextile blocked by residual soil particles were opened, and the drainage rate gradually increased. But beyond 20 times/min, the drainage rate did not significantly increase, suggesting that all channels previously blocked by residual soil particles had likely been opened. This indicates that, under residual soil particles, the T2 and T3 geotextiles can enhance the drainage efficiency through consistent vibration, and the drainage speed increases with the frequency of mallet strikes.

Based on these results, it is recommended to use T3 geotextile, a 200 g·m⁻² thermal-bonded nonwoven geotextile, for practical engineering applications. Additionally, it is suggested that simple vibration devices be installed at the geotextile drainage sections during sediment filling to accelerate the drainage process. This method can effectively enhance drainage efficiency, providing a better solution for the Yellow River sediment filling reclamation.

4.3. Implications and Future Prospects

The technology used to restore the Yellow River sediment filling reclaiming in collapsed mining areas holds vast potential for land resource restoration and mining subsidence management [36]. The use of efficient drainage geotextiles and vibration devices not only expedites the reclamation process but also mitigates the environmental impact of sediment. Although the initial investment is relatively high, the overall economic benefits are substantial due to reduced maintenance costs and shortened construction periods [37]. The geotextile performance evaluation method and application scheme proposed in this study provide strong technical support for the broader application of this technology. By scientifically selecting the appropriate geotextiles and combining them with optimal engineering application methods, it is possible to effectively address the challenges of sediment loss and drainage, thereby enhancing the efficiency of filling reclamation [20]. Furthermore, the findings of this study can serve as a reference for similar projects, such as reservoir sedimentation management and ecological restoration [38]. Future research could focus on improving geotextile materials, refining performance evaluation methods, and optimizing application schemes [39]. With in-depth study and continuous innovation, the technology used to drain Yellow River sediment filling reclamation will achieve greater advancements, significantly contributing to managing mining subsidence and the sustainable utilization of land resources.

5. Conclusions

This study addresses the application of geotextiles in the drainage of the Yellow River sediment filling reclamation, proposing an improved method for evaluating geotextile performance and validating the effectiveness of selected geotextiles through laboratory experiments. The findings provide a scientific basis for geotextile selection and application in Yellow River sediment filling reclamation, enhancing the reclamation efficiency and land resource utilization. The main conclusions are as follows:

(1)

An evaluation index system for geotextile performance suitable for the Yellow River sediment filling reclamation drainage was established. This system includes indicators such as permeability coefficient, changes in permeability coefficient under 20 kPa pressure, apparent opening size, gradient ratio, and soil retention rate. The entropy weight method was used to determine the weights of these indicators, identifying two specifications of thermal-bonded nonwoven geotextiles (250 g·m⁻² (T2) and 200 g·m⁻² (T3)) with an optimal drainage performance under the Yellow River sediment filling reclamation conditions.

(2)

Laboratory flume drainage tests demonstrated that both the T2 and T3 geotextiles effectively reduced the moisture content of the drained sediment. Compared to untreated sediment (CK), geotextile treatments significantly enhanced the lateral drainage, validating the reliability of the evaluation model for the Yellow River sediment filling reclamation drainage conditions.

(3)

The study found that striking the geotextile drainage sections with a mallet during sediment filling can stabilize the drainage speed and significantly improve the drainage efficiency. Considering both drainage effectiveness and economic costs, using the 200 g·m⁻² thermal-bonded nonwoven geotextile (T3) and installing simple vibration devices during the filling process to achieve stable and optimal drainage effects is recommended.