Effect of Uniaxial Tension on the Permeability of Geotextile-Sand System under Different Water Flow Conditions

Abstract

To investigate the influence of uniaxial tension on the permeation characteristics of the Geotextile-sand system under different water flows, a self-developed multifunctional gradient ratio permeameter was used to conduct relevant permeation tests on three commonly used geotextiles in engineering. The study, respectively, explores the variations in seepage velocity and gradient ratio of the Geotextile-sand system under different uniaxial tension strains with unidirectional water flow and reciprocating water flow, as well as the effects of different water flows on the system under the same uniaxial tension strain. The test results indicate that the trends of gradient ratio and seepage velocity in geotextiles are consistent under different water flows; however, the gradient ratio under reciprocating flow is smaller, while the seepage velocity is greater compared to unidirectional flow.

1. Introduction

Geotextiles, made from natural or synthetic polymers, serve functions such as drainage, filtration, and protection [1,2]. Geotube, made from geotextiles filled with loose or sandy soil, offer advantages like cost savings, prevention of soil erosion and loss, adaptability to various complex terrains, and rapid construction [3]. These benefits have led to their widespread application in numerous estuary and coastal embankment projects, as well as flood control and disaster relief efforts, both domestically and internationally. However, in actual engineering practices, the dewatering and consolidation rate of geotube is a key factor affecting the construction period. This rate mainly depends on the permeability of the geotube. Therefore, an in-depth study of the permeability characteristics of the heterogeneous system composed of geotextiles and sandy soil is of great significance for accurately predicting the dewatering and consolidation time of geotube, thereby reducing construction time and costs.

Guohang Tang et al. studied the impact of the placement position and number of layers of geotextiles on the permeability characteristics of soil, deriving the relationship between the burial depth of geotextiles and the soil’s permeability coefficient [4]. Song Wei et al. conducted clogging tests on non-woven geotextiles with different equivalent pore sizes, summarizing the variation patterns of gradient ratio, permeability coefficient, and clogging mechanisms [5]. Jianying Bai et al., through their analysis of various standards for testing the permeability of geotextiles, proposed the optimal fitting formula for the relationship between head difference and flow velocity [6]. Hong Jiang et al., in their study of vertical permeability tests on geotextiles, concluded that the inapplicability of Darcy’s law to all permeability studies was due to the uneven distribution of pores and differences in fabric morphology [7]. Chunxue Du et al., through long-term permeability tests, established the relationship between the permeability coefficient and time [8].

Studies on the Direction of Force Applied to Fabrics are as follows: Liu et al. proposed a method for measuring the circumferential tensile strength of geotextiles [9]. Meili Zhan et al., through large-scale indoor strain-seepage coupling model experiments, determined the impact of overburden stress on the permeability characteristics and anisotropy of geotube aggregates [10]. Xiaoguo Zheng et al., through puncture strength tests on geotextiles, elucidated the deformation mechanism and dual-peak mechanism during puncture failure [11]. Analyses of the Overall System are as follows: Malik et al. concluded that the permeability performance of geotube is related to the density of the filling materials [12]. Bo Zhou et al. found that different fabrics show varying permeability coefficients with the increase in the gradient ratio [13]. Chao Xu et al. proposed consistent conclusions on the filtration mechanism [14]. Practical Engineering Applications are as follows: Haimin Wu et al., using bag dewatering experiments and slurry sedimentation tests, provided references for coastal geotube projects [15]. Fourie et al., through an improved hydrodynamic sieving technique, analyzed the tensile load-bearing capacity of geotextiles [16]. Catre et al., using photogrammetry, studied the characteristics of geotube under certain strain conditions [17]. Wu et al. conducted water permeability and gradient ratio experiments on fabrics after uniaxial tension [18]. Fourie et al., using an improved hydrodynamic sieving technique, performed unidirectional and bidirectional tensile tests on geotextiles of different thicknesses, finding that tensile force significantly affects the permeability characteristics of fabrics [16]. Guohui Lei et al. indicated that bidirectional tensile enhances the overall water permeability of fabrics, while warp and weft tensile show differences in effective pore size changes [19]. Xiaolei Man et al., through indoor bag dewatering experiments, indirectly demonstrated that the permeability performance of filled geotube differs under warp and weft tensile [20].

In practical engineering, geotubes are primarily used in flood control, coastal protection, and land reclamation projects [21]. In these environments, geotubes are mainly subjected to periodic water flow [22]. However, previous studies have not considered the combined effects of tensile direction, tensile stress magnitude, and water flow direction on the permeability characteristics of the Geotextile-sand system. Therefore, this paper focuses on investigating the permeability characteristics of the Geotextile-sand system under unidirectional and reciprocating water flow. By applying uniaxial tension forces in different directions and magnitudes to the geotextiles, we analyze the variation patterns of relevant parameters, such as water permeability and gradient ratio. This comprehensive study aims to reveal the impact of different tensile directions and stresses on the permeability characteristics of the Geotextile-sand system under various water flow conditions.

2. Materials and Methods

Based on the characteristics of the Geotextile-sand system and the experimental setups of various researchers, a multifunctional gradient ratio permeameter capable of operating under both unidirectional and reciprocating flow conditions was independently developed, as shown in Figure 1.

The device consists of three main parts, as follows: a unidirectional-reciprocating water flow converter, a gradient ratio permeameter, and a data acquisition and analysis unit. The water flow converter provides different directional water flows to the Geotextile-sand system within the gradient ratio permeameter. Subsequently, the data acquisition and analysis unit measures the gradient ratio and seepage velocity of the Geotextile-sand system under these conditions.

Based on practical engineering considerations, this experiment selected three commonly used specifications of geotextile woven fabrics with weights of 100 g/m², 120 g/m², and 150 g/m². To avoid the occurrence of clogging in the fabric during the experiment, which could prevent the test from continuing normally, a well-graded, non-continuous soil with good filtration characteristics was chosen. This soil was composed of fine sand, medium sand, and coarse sand, mixed in certain proportions. To minimize the impact of excessive variables on the experiment, the proportion of fine sand was consistently maintained at 10%, while the proportions of the other sand grain sizes are shown in

Table 1. Mass percentage of each grain size interval in the soil sample.

Fine Content	Characteristic Particle Size (mm)			Cu	Cc
	d10	d30	d60
10%	0.0075	0.173	0.600	8.000	0.660

.

Before starting the Geotextile-sand permeability test, the geotextile to be used in the experiment was cut to a size suitable for tensile testing, and the sand for the experiment was prepared according to the sand mix scheme. Using a YG028GS high-temperature tensile testing machine (Wenzhou Jigao Testing Instrument Co., Ltd., located in Wenzhou, China), the cut geotextile was stretched at a speed of 6 mm/s to achieve tensile strains of 0%, 3%, 6%, and 9% in both the warp and weft directions.

The stretched geotextile was then fixed to the flanges of the upper and lower cylinders of the permeability device, secured with bolts to ensure good sealing performance, and a layer of copper wire mesh was placed on top of the fabric as a filtration layer. The prepared sand was then mixed uniformly and loaded into the test device in four stages. To ensure stability among the sand particles, the sand was compacted while being filled. After filling, another layer of copper wire mesh was placed on top to prevent the soil sample from being lifted by the water flow during the test.

(1)

Unidirectional Flow Geotextile-Sand Permeability Test: After assembling the apparatus, ensure that the water flow through the gradient ratio permeameter is unidirectional by adjusting the flow regulator. Fill the permeability device with water and let it stand for 24 h before conducting the unidirectional flow Geotextile-sand permeability test. During the test, the data acquisition and processing device is used to collect data either in real-time or at scheduled intervals for subsequent analysis.

(2)

Reciprocating Flow Geotextile-Sand Permeability Test: After assembling the apparatus and filling the permeability device with water, let it stand for 24 h. Then, set the flow regulator to ensure that the water flow through the gradient ratio permeameter is a reciprocating flow with a sine period of (T = 32 h). Conduct the permeability test under these conditions. During the test, the data acquisition and processing device is used to collect data either in real-time or at scheduled intervals for subsequent analysis.

Upon completion of the permeability tests, use Darcy’s law to determine the seepage velocity and gradient ratio for each test. Establish relevant variation curves to analyze the relationship between the seepage velocity and gradient ratio.

The experimental flowchart is shown in Figure 2.

3. Results

Based on the experimental data, analyze the relationships between the following parameters: the seepage velocity and gradient ratio of the Geotextile-sand system under unidirectional and reciprocating water flow with different tensile strains in different directions, the seepage velocity and gradient ratio of the Geotextile-sand system over time under different tensile strains and reciprocating water flow in different directions, and the seepage velocity and gradient ratio of the Geotextile-sand system under different water flows with the same tensile strain. Finally, further analyze the intrinsic connections through changes in porosity.

3.1. The Effect of Tensile Strain on the Seepage Velocity and Gradient Ratio of the Geotextile under Unidirectional Flow

3.1.1. Seepage Velocity

The relationship between seepage velocity and tensile strain obtained from the Geotextile-sand permeability tests under constant head for three different specifications of geotextiles is shown in Figure 3.

Figure 3a depicts the variation curves of seepage velocity with the tensile strain for different specifications of Geotextile-sand systems under warp tensile. According to the trends observed in the curves, the seepage velocity of different Geotextile-sand systems initially decreases significantly, and then slightly increases with the increase in tensile strain. Specifically, the seepage velocity decreases sharply from 0% to around 3% tensile strain. Although the subsequent seepage velocity increases slowly, it remains lower than the seepage velocity at 0% tensile strain. This indicates that the warp tensile of the geotextile increases the clogging degree of the Geotextile-sand system, with the most severe clogging occurring around 3% tensile strain. Under the same tensile strain, the seepage velocity of the Geotextile-sand system follows the trend of W120 > W150 > W100, indicating that under the same tensile strain, the seepage velocity is highest for W120 geotextiles and lowest for W100.

Figure 3b shows the variation curves of seepage velocity with the tensile strain for different specifications of Geotextile-sand systems under weft tensile. Analysis of the graph indicates that the seepage velocity of different Geotextile-sand systems increases with the increase in tensile strain. Between 3% and 6% tensile strain, the seepage velocity increases slowly, suggesting that the clogging condition of the geotextile improves poorly within this strain range. Under the same tensile strain, the trend of seepage velocity with different geotextile specifications is consistent with the trend observed under warp tensile.

A comprehensive analysis of Figure 3 shows that for the same geotextile, the Geotextile-sand system exhibits the highest seepage velocity under weft tensile, followed by the unstretched condition, with the lowest seepage velocity observed under warp tensile. This indicates that the weft tensile helps to improve the clogging condition of the geotextile.

3.1.2. Gradient Ratio

The clogging degree of geotextiles is a crucial factor in determining the lifespan of the geotextile filter layer. In practice, the clogging degree is primarily assessed using the gradient ratio (GR). Based on the experimental apparatus and data, the gradient ratio under stable head conditions in the experiments is calculated using the following formula:

$$H_{1-2}=H_2-H_1$$

(1)

$$H_{2-3}=H_3-H_2$$

(2)

$$GR={\displaystyle \frac{25}{25+\delta }}\times {\displaystyle \frac{H_{1-2}}{H_{2-3}}}$$

(3)

In the formula, H₁, H₂, and H₃ correspond to the water head heights measured by pressure measurement tubes one, two, and three in Figure 1, respectively. The head differences between H₁₋ and H₂₋₃ represent the water head differences between these points. δ is the thickness of the geotextile. The value 25 represents the height of each layer of sand fill. The gradient ratio GR is dimensionless, and the units for the other related quantities are in centimeters. The gradient ratio images obtained using the above formula are shown in Figure 3.

As shown in Figure 4a, under warp tensile strain, the gradient ratio of the Geotextile-sand system initially increases significantly, and then decreases slightly with the increase in tensile strain. Specifically, when the tensile strain ranges from 0% to approximately 3%, the gradient ratio increases sharply, followed by a slight decrease, but ultimately remains higher than the gradient ratio at 0% tensile strain. This indicates that clogging is severe at around 3% warp tensile strain, making the geotextile’s filter layer the most susceptible to damage, and resulting in the lowest seepage velocity. Under the same tensile strain, the gradient ratio of different Geotextile-sand systems follows the trend of W120 > W150 > W100.

According to Figure 4b, under weft tensile strain, the gradient ratio of the Geotextile-sand system decreases with the increase in tensile strain. The change is relatively small, between 3% and 6% tensile strain, indicating that the anti-clogging performance of the geotextile improves poorly under weft tensile strain in this range. Under the same tensile strain, the relationship between the gradient ratios of different Geotextile-sand systems is consistent with that under warp tensile strain.

Overall, as shown in Figure 4, for the same geotextile under no tensile, warp tensile, and weft tensile conditions, the gradient ratio follows the order of weft tensile < no tensile < warp tensile. This indicates that the weft tensile of the geotextile helps to improve the clogging condition, but reduces the lifespan of the filter layer.

3.2. The Effect of Tensile Strain on the Seepage Velocity and Gradient Ratio of Geotextiles under Reciprocating Water Flow

3.2.1. Seepage Velocity

Permeability tests were conducted on geotextiles with tensile strains of 0% and 3% under reciprocating water flow, and the relationship between seepage velocity and time was obtained, as shown in Figure 5. In the figure, the downward flow direction is defined as positive, and the upward flow direction is defined as negative.

Figure 5 indicates that under reciprocating water flow conditions, the seepage velocity of the Geotextile-sand system exhibits a clear periodic pattern. The recurrence period of the peak values is consistent with the minimum positive period. As the test progresses, the positive peak values of the Geotextile-sand system show no significant change, while the negative peak values decrease and eventually stabilize.

For the same geotextile, the relationship between seepage velocity and tensile direction is as follows: weft tensile > no tensile > warp tensile. This trend is consistent with the seepage velocity behavior of the Geotextile-sand system under unidirectional water flow.

3.2.2. Gradient Ratio

It is equally important to determine the effective lifespan of the geotextile filter layer under reciprocating water flow. Therefore, calculating the gradient ratio of the geotextile to assess its clogging degree is essential for indirectly reflecting the lifespan of the geotextile filter layer. Using a similar calculation method to that employed for the unidirectional flow, the experimental data for the reciprocating flow were processed to obtain the gradient ratio variation with time, as shown in Figure 6.

Figure 6 indicates that under reciprocating water flow, the gradient ratio of the Geotextile-sand system also exhibits a clear periodic pattern over time. The recurrence period of the peak values is consistent with the minimum positive period. The relationship between the gradient ratio and tensile strain for different geotextiles follows the trend of warp tensile > no tensile > weft tensile. Additionally, the gradient ratio for the reverse water flow gradually decreases and eventually stabilizes.

3.3. Comparative Analysis of Unidirectional Flow and Reciprocating Flow Tests under the Same Tensile Strain

3.3.1. The Impact of Reciprocating Flow and Unidirectional Flow on the Seepage Velocity of Geotextiles

Based on the previous analysis, the seepage velocity of the Geotextile-sand system under periodic reciprocating water flow exhibits clear periodic changes over time. The peak seepage velocity decreases gradually and eventually stabilizes; however, even when the subsequent changes become relatively stable, it is not convenient to compare these values directly to the constant values under unidirectional flow. Therefore, the following approach is taken for the Geotextile-sand system under reciprocating flow conditions: select a complete cycle where the peak seepage velocities have stabilized. The total water flow through the fabric during this complete cycle is divided by the period to approximate the average seepage velocity of the Geotextile-sand system during that cycle. For the Geotextile-sand system under unidirectional flow conditions, the final stable seepage velocity value is used.

Permeability tests were conducted on three different specifications of geotextiles with tensile strains of 0% and 3% under both unidirectional and reciprocating water flow. The seepage velocities obtained using the aforementioned processing method are shown in Figure 7.

Figure 7 shows that when the tensile direction is consistent and the same tensile strain is applied, the average seepage velocity of different Geotextile-sand systems under reciprocating flow is greater than the stable seepage velocity under unidirectional flow. As seen in Figure 8, the periodic water flow under reciprocating conditions periodically scours the upper and lower surfaces of the geotextile, making it easier for gravel to leave the pores on the fabric surface, thus reducing clogging and increasing the effective pore size of the fabric surface. Therefore, under the same tensile strain, the average seepage velocity of the geotextile under reciprocating flow is greater than the stable seepage velocity under unidirectional flow. However, a common trend is observed for different geotextiles under different water flow conditions, which is as follows: weft tensile > no tensile > warp tensile.

3.3.2. The Impact of Reciprocating and Unidirectional Flow on the Gradient Ratio of Geotextiles

It is equally important to explore the impact of reciprocating water flow and unidirectional water flow on the gradient ratio of geotextiles. After processing the gradient ratio under reciprocating flow similarly to the seepage velocity, a comparison with the gradient ratio under unidirectional flow is shown in Figure 9.

As illustrated in Figure 9, under the same tensile strain, the gradient ratio of the Geotextile-sand system is greater under unidirectional flow than under reciprocating flow. The relationship regarding tensile direction is as follows: warp tensile > no tensile > weft tensile. This indicates that the anti-clogging performance of the geotextile is significantly improved under reciprocating water flow.

Combining this with Figure 8 and the analysis of seepage velocity, it is evident that the filter layer of the geotextile is more prone to damage under reciprocating flow, thereby reducing its lifespan.

3.4. Analysis of the Impact of Uniaxial Tension on Geotextiles

3.4.1. Analysis of the Impact of Uniaxial Tension on the Pores of Geotextiles

To investigate the impact of uniaxial tension strain on the pores of geotextiles, MATLAB was used to threshold images of geotextiles under different tensile states. By analyzing and calculating the porosity of the fabric under various tensile conditions, the mechanism affecting its permeability performance can be revealed.

According to Figure 10a, the porosity distribution of the geotextile is uneven when unstretched, with some areas showing no pores. This is related to practical factors. On one hand, current technology cannot produce geotextiles with uniformly distributed pores; on the other hand, collisions and compressions during transportation and storage can cause the warp and weft of the geotextile to shift.

Figure 10b,c show that after the geotextile is stretched, the pore distribution becomes more uniform. The pores of the geotextile under weft tensile strain are noticeably more numerous and larger than those under warp tensile strain. This relates to the structure of the geotextile shown in Figure 11. The weft fibers are straight, while the warp fibers are curved. When tensile strain is applied, the weft fibers are pulled tight, increasing in length and decreasing in width, thus creating more and larger pores. For the warp fibers, the applied tensile stress straightens the curved fibers, making the pores smaller initially, but similar to the weft fibers, they eventually increase in number. These specific changes are illustrated in Figure 12.

Figure 12 shows that under the same tensile strain, the porosity of the three geotextile types follow the order of W120 > W150 > W100. For a given geotextile, increasing warp tensile strain initially decreases porosity, and then increases it, with the minimum porosity around 3% tensile strain. For weft tensile strain, increasing tensile strain continuously increases porosity. This is consistent with the seepage velocity images of the Geotextile-sand system in Figure 3. It indicates that tensile strain mainly alters the permeability characteristics of the Geotextile-sand system by changing the porosity of the fabric. The differences observed under unidirectional and reciprocating water flow suggest that the scouring of the fabric surface by water flow (i.e., reducing the clogging of the fabric by sand particles) is also a significant factor affecting the permeability characteristics of the Geotextile-sand system.

3.4.2. Analysis of the Impact of Uniaxial Tension on the Permeability of Geotextiles

By analyzing the changes in the pores of geotextiles after tensile, it was found that these changes significantly impact the permeability characteristics of the Geotextile-sand system. To further investigate the variations in permeability characteristics of geotextiles under tensile conditions, a permeability test was conducted using the apparatus shown in Figure 11. This test focused on the permeability of geotextiles under uniaxial tension strain [23].

The experimental procedure is as follows:

After soaking the stretched geotextile for 24 h, it was fixed in the position shown in the diagram, ensuring the apparatus was well-sealed. Deionized water was slowly injected into the apparatus through the valve-controlled water pipe until the deionized water just contacted the geotextile. At this point, the injection was immediately stopped, and the valve was closed. Deionized water was then slowly injected along the inner wall of Pipe A until the water level was 3 cm below the pipe opening, at which point the injection was stopped. After the water level within the apparatus stabilized, the camera was started, and the valve was quickly opened. Recording continued until the water levels on both sides were equal, at which point the recording was stopped. The recorded video was imported into a custom program for frame-by-frame analysis. The resulting head difference (H) versus time (T) graph is shown in Figure 12.

The Data Processing Method is as follows:

The average flow rate was used to approximate the overall flow rate. The geotextile permeameter used in the experiment, as shown in Figure 12, has identical diameters for the water pipes at both ends. This means that, within the same time interval, the height that the water level drops to in Pipe A equals the height that it rises to in Pipe B. Since this experiment was conducted under laminar flow conditions, Darcy’s law is applicable [5].

According to Darcy’s Law,

$$v=Kj$$

(4)

From the hydraulic gradient,

$$j={\displaystyle \frac{H}{\delta }}$$

(5)

We derive

$$v={\displaystyle \frac{KH}{\delta }}$$

(6)

Let

$$\psi ={\displaystyle \frac{K}{\delta }}$$

(7)

where $\psi$ is the permeability.

Thus,

$$v=\psi H$$

(8)

According to the integral relationship,

$$v=-{\displaystyle \frac{dh}{dt}}$$

(9)

where

$$dH=2dh$$

(10)

Substituting back into Equation (8),

$$\psi dt=-{\displaystyle \frac{1}{2}}\cdot {\displaystyle \frac{1}{H}}dH$$

(11)

Integrating Equation (11),

$$\psi t=-{\displaystyle \frac{1}{2}}\cdot \mathit{ln}H+C$$

(12)

Eliminating the integration constant term gives

$$\psi \left(t_2-t_1\right)={\displaystyle \frac{1}{2}}\cdot \mathit{ln}\left({\displaystyle \frac{H_1}{H_2}}\right)$$

(13)

Simplifying yields,

$$H=e^{\left(At+B\right)}+C$$

(14)

where

$$\psi =-{\displaystyle \frac{A}{2}}$$

(15)

Based on Equation (11), the data from the graph shown in Figure 13 were fitted. The fitted values of the head difference for the geotextile, when the changes over time have stabilized, were then plotted against the tensile strain applied to the geotextile. The resulting graph is shown in Figure 14.

As shown in Figure 15, the permeability of the geotextile under warp tensile strain initially decreases, and then increases with increasing strain. Under weft tensile strain, the permeability increases with increasing tensile strain. This trend is consistent with the seepage velocity patterns of the Geotextile-sand system discussed earlier.

Analyzing this in conjunction with Figure 13, it is evident that tensile strain alters the permeability of the geotextile by changing its pore structure. However, the changes in the permeability trends of the geotextile shown in Figure 15 do not completely match the seepage velocity trends of the Geotextile-sand system discussed previously. This discrepancy suggests that while the change in porosity due to tensile strain is a major factor affecting the permeability characteristics of the Geotextile-sand system, other factors, such as the thickness of the geotextile, the distribution of pores, and the filtration properties of the fill material, also play significant roles in influencing the overall permeability characteristics in practical applications.

4. Discussion

• The research results indicate that there are significant differences in the mechanical behavior and permeability performance of geotextiles under warp and weft tensile strains, reflecting the substantial impact of the weaving characteristics on the tensile properties of geotextiles. Therefore, in studies involving unidirectional tensile tests of geotextiles, it is essential to strictly distinguish between warp and weft directions. Moreover, in studies involving bidirectional tensile behavior of geotextiles, especially under unequal strain conditions, the effect of tensile direction on permeability performance should also be a focus. Since geotextiles in practical engineering applications are often subjected to complex bidirectional stresses, in-depth research on their permeability characteristics under bidirectional tensile conditions will help to more comprehensively understand their behavior under complex mechanical conditions. Therefore, future research should further explore the impact of bidirectional tensile strains under unequal strain conditions on the permeability performance of geotextiles, providing a greater theoretical basis for practical engineering applications.
• This paper conducted a preliminary study on the permeability performance of geotextiles under reciprocating water flow, and the results showed significant differences between the effects of reciprocating and unidirectional water flows. However, the research on the permeability performance of geotextiles under reciprocating water flow is still insufficient. Future research should consider more complex experimental conditions, such as different water flow cycles, various types of geotextiles, and different hydraulic gradients, to systematically investigate the influence of these factors on permeability performance. Additionally, long-term reciprocating water flow may lead to gradual changes in the permeability characteristics of geotextiles, which is of great significance for practical engineering. Moreover, alternating reciprocating and unidirectional water flows is quite common in practical engineering scenarios, and, thus, further in-depth studies on the permeability characteristics of geotextiles under such complex working conditions are needed to better guide engineering practices and design.

5. Conclusions

This study systematically investigated the Geotextile-sand system under different tensile strains and water flow conditions using a self-developed multifunctional gradient ratio permeameter. The study examined the seepage velocity and gradient ratio of three different specifications of geotextiles (W100, W120, and W150) under unidirectional flow with warp or weft tensile strains of 0%, 3%, 6%, and 9%. It also explored these parameters under reciprocating water flow with warp or weft tensile strains of 0% and 3%. Additionally, the study compared these parameters under unidirectional and reciprocating water flow conditions to warp or weft tensile strains of 0% or 3%. The following conclusions were drawn:

• Impact of Uniaxial Tension Strain: Uniaxial tension strain affects the permeability characteristics of the Geotextile-sand system by altering the porosity of the geotextile. Within the range of 0% to 9% tensile strain, under warp tensile strain, the porosity of the geotextile initially decreases, and then increases as the tensile strain increases. From 0% to 3% tensile strain, the continuously decreasing porosity leads to a decrease in the seepage velocity of the Geotextile-sand system. From 3% to 9% tensile strain, the increasing porosity results in a gradual increase in seepage velocity. Under weft tensile strain, within the range of 0% to 9%, the porosity increases continuously with increasing tensile strain, leading to an increase in the seepage velocity of the Geotextile-sand system.
• Impact of Unidirectional and Reciprocating Water Flow: Both unidirectional and reciprocating water flow affect the permeability characteristics of the Geotextile-sand system by altering the clogging of the geotextile. Within the range of 0% to 9% tensile strain, under reciprocating water flow, the periodic scouring of the geotextile surfaces by water flow dislodges sand particles from the fabric pores, reducing clogging and increasing the seepage velocity of the Geotextile-sand system. Consequently, the seepage velocity of the geotextile under reciprocating flow is higher than under unidirectional flow.