A Study on the Long-Term Tensile Strength Properties of the Geotextile Tubes

Abstract

This study examines the tensile behavior of both plain and seamed geotextiles. Samples were taken from two geotextile tube test beds, one made of composite materials and the other of woven materials, constructed in 2013 and 2016, respectively, in the Saemangeum reclaimed area. These test tubes have been exposed to marine conditions and sunlight for 10 and 8 years, respectively. Based on sunlight exposure, samples of plain and seamed geotextiles were collected from both exposed (top) and non-exposed (bottom) locations. The tensile strength–strain curves, strength degradation, and seam efficiencies of the original samples were compared with those exposed to marine environments and sunlight for 8–10 years. Geotextile tubes have been found to function normally even after being exposed to seawater and sunlight for 8–10 years, with sunlight being identified as the most significant factor affecting long-term tensile strength. The influence of seawater on tensile behavior is minimal, and it was observed that the tensile strength of the seam after 8–10 years is only about 10–19% of the initial plain tensile strength. Nevertheless, the tubes operate without failure, suggesting that the earth pressure acting on stabilized geotextile tubes is relatively low. These findings offer valuable insight into the long-term durability of geotextiles tubes under harsh environmental conditions and serve as a reference for future applications.

1. Introduction

Geotextile tubes are widely used in land reclamation projects [1,2], the construction of embankments [3,4], temporary platforms for bridge works [5,6,7], pipeline protection [8], and various ecological functions along coastlines [9,10,11,12,13] due to their eco-friendly sustainability. These geotextile materials are exposed to various environmental stressors, including ultraviolet (UV) radiation, oxygen, and dynamic forces such as waves, currents, and tides. Prolonged exposure to these elements can degrade the physical and mechanical properties of geosynthetics, ultimately compromising their performance and reducing their service life. Among the different performance parameters, tensile strength is one of the most critical indicators of long-term durability. Therefore, evaluating the long-term tensile behavior of geotextile tubes is essential for ensuring their reliability in field applications.

Polypropylene (PP) and polyethylene terephthalate (PET) are the most commonly used polymers in the manufacturing of geotextile tubes [14]. PP exhibits strong chemical resistance to water, acids, and alkalis [15], while PET performs well in high-temperature conditions [16]. Koerner et al. [17], examined the long-term durability and aging characteristics of geotextiles subjected to thermal, chemical, and UV exposure. The study concluded that material type, particularly polymer composition, plays a key role in resistance to degradation, with UV exposure being the most damaging over time, investigated the mechanisms influencing the long-term filtration behavior of geotextiles under sustained flow conditions. The study found that clogging driven by physical, chemical, and biological processes significantly affects filtration efficiency over time. Rollin and Lombard [18], investigated the photo-initiated degradation of geotextiles using accelerated UV aging methods to simulate long-term sunlight exposure. The study revealed that UV radiation significantly reduces tensile strength, especially in PP geotextiles, and emphasized the importance of UV stabilizers and protective coverings for extended service life. Hsieh et al. [19], investigated the effects of UV exposure on plain geotextiles made of polypropylene (PP) and polyester (PET) over a 12-month period. They reported that UV radiation was the primary cause of tensile strength degradation, while the influence of seawater was minimal. Carneiro et al. [20], studied the impact of stabilization packages on non-woven polypropylene geotextiles in a marine environment over 36 months. Their study found that the geotextile exhibited good resistance to seawater and that the accumulation of algae and dirt provided protection from UV degradation.

Although previous studies have evaluated the long-term performance of plain geotextiles over durations ranging from 6 to 36 months, these investigations were largely conducted under controlled conditions and do not fully capture the effects of real-world environmental exposures. In the case of seamed geotextiles, although research on seaming methods exists [21,22], there is a notable lack of studies addressing their long-term tensile behavior and seam efficiency under field conditions. This study fills that gap by offering an evaluation of the long-term tensile performance of both plain and seamed woven and composite geotextile materials subjected to marine environments, land reclamation processes, and prolonged UV exposure over a period of 8 to 10 years, a timeframe rarely investigated in prior research.

The objectives of this study are, first, to present the detailed configuration of geotextile tubes used in land reclamation, including the selection of both plain and seamed geotextile tube samples from various locations based on exposure. Furthermore, the study aims to evaluate the tensile strength of both plain and seamed geotextile materials. This includes a focus on woven and composite geotextile types. In addition, the study assesses the long-term stability of geotextile tubes in accordance with Standards [23,24] under real field conditions. The findings of this study provide a valuable reference for the long-term application of geotextile tubes in land reclamation projects.

2. Overview of Field Test Geotextile Tube Configuration

To investigate the long-term tensile behavior of the geotextile tubes, a field test site was selected in the land reclamation area located in Saemangeum, South Korea. Two test tubes were used: one made of composite geotextile material (tube 1) and the other as a connection tube made of woven geotextile (tube 2). Section 2.1 and Section 2.2 explain the background of the field test tube 1 and field test tube 2 configurations, respectively.

2.1. Test Tube 1

The field test tube 1 was formed by joining individual sheets in the transverse direction (see Figure 1a). The process of joining individual sheets is referred to as seaming, which involves the stitching. Each transverse sheet has dimensions of 16 m in length (L) and 4 m in width (W). These sheets were connected through a transverse seam, employing a two-row, six-line stitching method. The seam featured an inter-stitching spacing (L1) of 1 cm and a stitching row width (L2) of 5 cm, as demonstrated in cross-section details A. The spacing between the rows of stitching (L3) was set at 10 cm.

Subsequently, both ends of all transverse sheets are joined using a longitudinal seam, as shown in Figure 1b with cross-section details B. The stitching spacing for the longitudinal seam remained consistent with that in section A. After joining the individual sheets through the seam, both ends of the tube were closed using a two-row, six-line stitching configuration to complete the tube.

2.2. Test Tube 2

The field test tube 2, geotextile tube, was a connection tube made of woven geotextile material. The configuration of the tube is shown in Figure 2, with further details provided in [5,7]. The method joins adjacent primary tubes using an auxiliary tube. Several parts of the geotextile sheets are joined to form a tube (primary or auxiliary), with this joining method, performed by the stitching, referred to as seaming. A prayer seam with 6 stitches and two rows of stitching was applied as shown in Figure 2b. Each seam is 5 cm long, with 1 cm distance between each stitch for both primary and auxiliary tubes. An additional 5 cm spacing between two seams were provided at the connection location. The sectional elevation of the filled tube is shown in Figure 2c.

2.3. Materials

Both field test tubes were filled using the dredged soil, classified as silty sand (SM) as per the USCS soil classification system. The water content and the specific gravity were 15.9% and 2.687, respectively. The test field tube 1 geotextile tube was made from composite material, with an outer layer comprising woven polyester (PET) and an inner layer made of non-woven polypropylene (PP). The apparent opening size (AOS) and the coefficient of permeability were 145 μm and 5.8 × 10⁻² m/s, respectively. The test field 2 connection tube was made of woven polyester geotextile material with an AOS of 315 µm and permeability of 8.5 × 10⁻⁵ m/s.

3. Sample Collection and Test Procedure

The sample collection locations for test tubes 1 and 2 are shown in Figure 3 and Figure 4, respectively. As illustrated, both plain and seamed geotextiles were exposed to sunlight on the surface (Figure 3a and Figure 4a), while the bottom sections remained unexposed to sunlight (Figure 3b and Figure 4b). In 2024, the tubes were opened, 10 years after installation for tube 1 and 8 years for tube 2, and samples were collected from various locations, including the top, bottom, front (tube 1), and top connection (tube 2). Both plain (warp and weft directions) and seamed geotextiles were sampled. In this manuscript, samples collected prior to the construction of the tubes are referred to as “original”, while those collected in 2024 are classified based on their location as “top”, “bottom”, “front”, or “connection”.

Table 1. Summary of the samples and test plan.

Test	2013 a/2016 b				2024 c
	Original			Top			Bottom		Front
	Plain	Seamed		Plain	Seamed	Connection d	Plain	Seamed	Seamed
		Trans.	Long.
									Trans.	Long. e
Sunlight	-	-	-	✔	✔	✔	-	-	✔	✔
Tensile test	✔	✔	-	✔	✔	✔	✔	✔	✔	✔
SEM	✔	-	-	✔	-	-	✔	-	-	-
No. of samples	1	1	-	5	5	5	5	3	5	3

^a,b The field test tubes 1 and 2 were constructed in 2013 and 2016, respectively. ^c The tube was opened in July 2024 for the sample collection to investigate the long-term tensile behavior. ^d Top connection is the part of seam that is stitched on the primary tube to connect primary tube with the auxiliary tube (see Figure 2b, detail A). ^e Longitudinal seam: Joining the transverse sheets (test tube 1) along the tube length (see Figure 1b, detail B).

summarizes the sampling plan and corresponding tests. Tensile strength tests were conducted on all samples to evaluate long-term tensile performance, with special attention to differences between plain and seamed materials. A total of thirty-one (31) samples were tested in this study. This includes one original plain and one seamed geotextile sample, both tested in 2013 prior to installation. As only a single specimen of each was available at that time, no additional original samples were available for further testing in 2024. In 2024, five (05) plain samples were collected from each tube, representing the top, front, and bottom locations. Additionally, five (05) seamed samples were collected from various seam locations, including the top, bottom, front transverse, front longitudinal, and connection areas. All collected samples were tested, except for the front longitudinal seam of tube 1 and the bottom seam of tube 2, where only three samples were tested in each case due to damage during the testing process. This sampling strategy was designed to evaluate both long-term exposure effects and the performance of different seam configurations under real field conditions. Furthermore, samples for scanning electron microscopy analysis (SEM), including the original sample, a sample from the top, and a sample from the bottom, were collected. The SEM analysis was conducted to provide a physical interpretation of the tensile behavior of the geotextile material.

The washed sample views in the lab are shown in Figure 5. The setup of the constant rate of extension (CRE) tensile test machine is shown in Figure 6. The tests were conducted in accordance with Standards [23,24] for plain and seamed geotextile samples. The samples were gripped into the roller clamp having a face width of 20 cm; the clear distance was set to be 10 cm for plain, and 40 cm for the seamed geotextile. The plain geotextile samples were tested for both the weft and wrap directions. The elongation was measured with the laser camera as shown in Figure 6.

4. Result

The long-term tensile strength evaluation was performed by comparing original samples (collected prior to construction) with samples exposed for 10/8 years in the test field. The original specimen test was conducted only on a single sample, while there are multiple samples (e.g., S1, S2, S3, S4, and S5) from the field test tubes, therefore, first the long-term average tensile strength (${\overline{S}}_t$) is calculated using Equation (1). The percentage tensile strength degradation is calculated using Equation (2).

$${\overline{S}}_t={\displaystyle \frac{\sum S_t}{n}}$$

(1)

$$\mathrm{S}\mathrm{t}\mathrm{r}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{t}\mathrm{h} \mathrm{D}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{a}\mathrm{d}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} (\%)={\displaystyle \frac{S_o-{\overline{S}}_t}{S_o}}\times 100$$

(2)

Here, S_o and S_t represent the tensile strength of the original sample and sample after 10/8 years, respectively.

4.1. Plain Geotextile Tensile Behavior

The tensile strength curves for the plain composite (tube 1) and woven (tube 2) geotextile’s weft and warp are shown in Figure 7 and Figure 8, respectively, representing samples collected from the bottom and top of the tube. For test tube 1 (composite geotextile), the tensile strength of the original samples was 178/185 kN/m for the warp/weft directions, respectively. In contrast, the samples collected from the bottom of the tube exhibited tensile strengths of 163 ± 5.5/168 ± 6.2 kN/m, while the top samples showed values of 77 ± 8.5/84 ± 1.74 kN/m (see Figure 9a). The percentage strength degradation calculated using Equation (2) is also presented in Figure 10a, showing 8/9.2% for the warp/weft of bottom samples and 56/54% for the top samples.

For test tube 2 (woven geotextile), the tensile strength of the original samples was 176/169 kN/m for the warp and weft directions, respectively. In contrast, the samples collected from inside the tube exhibited tensile strengths of 102 ± 9.8/167 ± 3.6 kN/m, while the surface-exposed samples showed values of 37 ± 2.3/61 ± 2.6 kN/m (see Figure 9b). The percentage strength degradation is also presented in Figure 10b, showing 42/0.96% for the warp/weft of inside samples and 79/64% for the surface-exposed samples.

In both geotextile tubes, the bottom sections exhibited negligible degradation, attributed to the lack of ultraviolet (UV) exposure. In contrast, the top sections showed significant deterioration due to prolonged exposure to sunlight. UV radiation is widely recognized as the primary driver of photodegradation in geotextiles; however, when these materials are buried or submerged, they are effectively shielded from UV rays, greatly minimizing the risk of degradation. This observation is consistent with findings of Koerner et al. [16] and Hsieh et al. [19], which documented similar effects of UV-induced degradation on geotextile materials. Although the degradation of the two tubes cannot be directly compared quantitatively, since tube 1 was exposed for 10 years and tube 2 for 8 years, the effects of UV-induced degradation appeared more pronounced in the woven geotextile of tube 2 than in the composite geotextile material of Tube 1.

The typical observed mode of failure for test tubes 1 and 2 is shown in Figure 11a,b, respectively. Tensile rapture at the ultimate stage is observed in both cases for composite as well as woven geotextiles, as shown in Figure 11. This failure mode is consistent across all location sample locations.

4.2. Seamed Geotextile Tensile Behavior

The long-term tensile strength evaluation at the seam location was performed by comparing the original sample with samples exposed for 10 and 8 years in the test field for test tube 1 and test tube 2 (see Figure 12 and Figure 13). For test tube 1, the original longitudinal seam strength was not available; therefore, the tensile strength curves of the specimens after 10 years for this location are only shown in Figure 12d.

The transverse seam strength for both the original sample and the bottom tube sample was observed to be comparable, with values of 159 kN/m and 143 ± 4.4 kN/m, respectively (see Figure 14a). The transverse seam strength of the exposed top and front geotextile was found to be 62 ± 2.2 kN/m and 61 ± 19.7 kN/m, respectively. The longitudinal seam strength was found to be 18 ± 0.8 kN/m. The transverse seam tensile strength degradation was found to be 10% and 61% for the bottom and the surface samples (see Figure 15a).

For test tube 2, the long-term tensile strength evaluation at the seam location was performed by comparing the original sample with samples exposed for 8 years in the test field (see Figure 13). The seam strength for both the original sample and the inside tube sample was observed to be comparable, with values of 149 kN/m and 126 ± 5.9 kN/m, respectively (see Figure 14b). Since the seam configuration was slightly different for the top seams at the primary/auxiliary tube and the connection location, separate seam strengths are presented for the top connection seam (see Figure 13c). The seam strength of the top geotextile was found to be 74 ± 3.6 kN/m, while the seam strength at the connection location was 31 ± 3.8 kN/m (see Figure 14b).

The long-term performance of a geotextile tube is also governed by its seam strength, as seams are often considered the weakest points. Therefore, it is important to investigate the long-term performance of the seams, which is typically expressed in terms of seam efficiency. Seam efficiency (E) is defined as the ratio of the tensile strength of the seam (T_seam) to that of the geotextile material (T_geotextile).

$$E (\%)={\displaystyle \frac{T_{seam}}{T_{geotextile}}}\times 100$$

(3)

For geotextile tube 1, the calculated seam efficiency was found to be 89% for the original sample, 81% for the bottom, and 35% and 34% for the surface top and front samples, respectively (see Figure 16a). The longitudinal seam efficiency was found to be 10%. For geotextile tube 2, the seam efficiency was found to be 88% for the original sample, 75% for the inside, 44% for the surface sample, and 19% for the surface at the connection location (see Figure 16b). It is typical for seam strength to be lower than that of the plain geotextile because stitching damages the filaments during the seaming. Visually, no broken stitches were observed after 10 and 8 years for tube 1 and tube 2, respectively. The seam efficiency of the original and the inside samples remains comparable. However, significant degradation in seam efficiency was observed for the samples exposed to sunlight for both tubes.

The typical tensile deformation mode comparison of the test tube 1 seamed geotextile before and after tests is shown in Figure 17. Before testing, the stitches were aligned and intact for both the transverse and the longitudinal seams. During the test, the sound of stitches breaking was heard in all the seam tests. As the tensile deformation increased, the stitches became distorted and significantly displaced from their original position. Additionally, yarn stretching and the rapture were observed in a few cases (see Figure 17a). However, the tensile deformation mode and the strength curves of the longitudinal seam were found to be unique. As shown in the tensile strength curves (Figure 12d), the first 200 mm extension resulted in the breaking of the first seam (see Figure 17b). Further extension led to the breaking of the seam stitches for seam 2; however, no rapture of the geotextile material was observed. It is worth noting that, although the tensile strength of the longitudinal seam was 18 kN/m with 10% efficiency, it remained functional over the 10-year period. However, it is recommended that the location of the longitudinal seam in future applications be at the bottom of the tube instead of the front or an exposed location.

The tensile deformation mode comparison of the test tube 2 seamed geotextile at the top primary/auxiliary and the top connection locations before and after tests is shown in Figure 18 and Figure 19, respectively. Before testing, the stitches were aligned and intact. During the test several, the sound of stitches breaking was heard in all the seam tests. As the tensile deformation increased, the stitches became distorted and significantly displaced from their original position. Additionally, yarn stretching and the rapture were observed in a few cases.

4.3. SEM Analysis

To better understand the long-term geotextile material tensile behavior, SEM images of the top and bottom samples were taken and are presented in Figure 20 and Figure 21 for the composite and woven material, respectively. The composite geotextile material comprises two layers: a woven part and a non-woven part. Therefore, SEM tests were performed on both sides of each sample. Since SEM images were not initially planned in 2013, the original samples in 2024 were unavailable, and therefore, SEM images of the original sample are not presented. The SEM images of the non-woven sides of both top (see Figure 20b) and bottom samples (see Figure 20d) were found to be similar, as neither side was exposed to sunlight. However, a significant difference in the condition of filaments was observed on the woven sides of the top (see Figure 20a) and bottom (see Figure 20c) samples. The woven side of the bottom sample appeared intact, with some traces of entrapped soil particles. In contrast, the woven filaments of the top samples showed significant damage due to the ultraviolet (UV) sunlight exposure.

In the case of test tube 2 woven geotextile sample, the filaments of the bottom sample (see Figure 21b) appear similar to those of the original sample (see Figure 21a), with some traces of entrapped soil particles. In contrast, significant filament degradation was observed in the top sample (see Figure 21c), which was subjected to the UV sunlight exposure.

Prolonged exposure to sunlight degraded the tensile strength of both composite and woven geotextile materials. UV radiation is widely recognized as the primary driver of photodegradation in geotextiles; however, when these materials are buried or submerged, they are effectively shielded from UV rays, greatly minimizing the risk of degradation [16,19]. However, both the plain geotextile and the seamed geotextile remained functional, with no visible damage observed, and the soil inside was retained. Therefore, the application of the composite geotextile is recommended for long-term use in land reclamation projects.

5. Conclusions

The findings from the long-term tensile strength evaluation highlight the effectiveness of using both composite and woven geotextile material tubes, as demonstrated by their successful field implementation after 10 and 8 years of harsh marine exposure, respectively. The key observations are as follows:

• Geotextile tubes have been found to function normally even after being exposed to seawater and sunlight for 10 and 8 years, with sunlight being identified as the most significant factor affecting long-term tensile strength.
• The long-term tensile strength evaluation of plain composite and woven geotextile materials revealed that both materials maintained comparable tensile strength in their original and bottom samples. However, significant degradation was observed in the exposed top samples. For composite geotextile material, tensile strength decreased from 178/185 kN/m (original) to 77 ± 8.5/84 ± 1.7 kN/m (top). Similarly, for woven geotextile material, tensile strength reduced from 176/169 kN/m (original) to 37 ± 2.3/61 ± 2.6 kN/m (top).
• The seam strength evaluation of both composite and woven geotextile materials demonstrated comparable tensile strength in original and bottom locations. However, significant degradation was observed in exposed samples. For composite geotextile material, seam strength reduced from 159 kN/m (original) to 62 ± 2.1~61 ± 19.7 kN/m (top and front). Similarly, for woven geotextile material, seam strength decreased from 149 kN/m (original) to 74 ± 3.6 kN/m (top) and further to 31 ± 3.8 kN/m at the connection location.
• For composite seamed geotextile material, the top samples showed seam efficiency of 35% for transverse and front longitudinal seam efficiency was found to be 10%. For woven seamed geotextile, while the surface-exposed samples showed seam efficiency of 44% for the top and 19% at the connection location. Nevertheless, both the tubes operate without failure, suggesting that the earth pressure acting on stabilized geotextile tubes is relatively low.
• For composite seamed geotextile material, the top samples exhibited a seam efficiency of 35% for the transverse seam, while the front longitudinal seam efficiency was found to be 10%. In the case of woven seamed geotextile material, the surface-exposed samples demonstrated a seam efficiency of 44% at the top and 19% at the connection location.
• Over a period of 8–10 years in a marine environment, the geotextile tubes remained stable and functional, despite relatively low seam efficiencies of 10% for the composite geotextile and 19% for the woven geotextile. These results demonstrate that, even with significant long-term material degradation, geotextile tubes can still fulfill their primary function of soil retention in land reclamation applications.