Mechanical, Degradation, and Impact Resistance of a Sustainable Coir Geotextile Composite Barrier for Landslide Mitigation

Abstract

Flexible barrier systems are widely used for landslide and debris flow mitigation due to their ability to dissipate impact energy through large deformations. Conventional systems, however, rely on steel mesh components, which are associated with high environmental impact and durability concerns. This study examines the feasibility of a sustainable coir geotextile composite barrier as an alternative flexible barrier for mitigating small-to-moderate landslides. A woven geotextile barrier was developed using multi-strand coir ropes and evaluated through a comprehensive experimental program involving physical and mechanical characterization, accelerated degradation testing, incremental static loading, vertical drop impact tests, and sustained load retention tests. The developed barrier exhibited a high mass per unit area of approximately 3750 g/m² and tensile capacities exceeding 2 kN at the rope level. Accelerated weathering tests revealed a limited reduction in tensile strength of approximately 5% after three years of exposure, whereas prolonged exposure of five years led to strength losses exceeding 70%, underscoring durability as a key design consideration. Static loading tests confirmed stable behavior up to 550 kg, and sustained loading of approximately 1700 kg was maintained over 48 h without loss of structural integrity. Vertical drop tests demonstrated impact resistance in the range of 6–51 kN, depending on the drop height, mass, and connection density. The results demonstrate that coir geotextile barriers can function as flexible, energy-dissipating composite systems suitable for sustainable landslide mitigation in moderate hazard scenarios.

1. Introduction

Landslides are among the most widespread and destructive natural hazards affecting mountainous and hilly terrains worldwide, frequently resulting in loss of life, damage to infrastructure, and long-term socioeconomic disruption [1,2,3]. Their occurrence is governed by a complex interaction of geological, geomorphological, hydrological, and climatic factors, with rainfall and seismic activity being the most common triggering mechanisms [4,5]. In many regions, shallow landslides, debris flows, and small-scale rockfalls dominate the failure mechanisms and are characterized by rapid onset, high mobility, and significant impact forces upon interaction with protective structures [6,7,8].

To mitigate the consequences of such hazards, a range of structural and non-structural measures has been developed. Among structural solutions, barrier systems installed across potential flow or fall paths play a crucial role in intercepting moving debris and reducing its momentum before it reaches vulnerable infrastructure [9,10]. Barrier systems can be broadly categorized into rigid and flexible types. Rigid barriers, such as reinforced concrete retaining walls and gravity structures, offer high stiffness and strength but often require substantial foundations and extensive construction efforts [11]. In contrast, flexible barrier systems, typically composed of high-tensile steel wire meshes supported by cables and anchors, provide adaptability to complex terrain, efficient energy dissipation, and reduced foundation requirements [7,8,12].

Flexible barriers have been widely adopted for debris flow and rockfall mitigation due to their ability to undergo large deformations while maintaining structural integrity. Their deformability allows a substantial portion of the incoming kinetic energy to be dissipated through mesh elongation, cable stretching, and progressive engagement of connections [13,14]. Experimental and numerical investigations have consistently shown that flexible systems generate lower peak impact forces compared with rigid structures, highlighting their effectiveness in impact mitigation [7,8,13]. However, conventional flexible barriers rely almost exclusively on steel components, which are associated with high embodied energy, susceptibility to corrosion in aggressive environments, and a considerable environmental footprint during production and installation [15].

In recent years, increasing emphasis has been placed on sustainable engineering materials that minimize environmental impact while maintaining adequate mechanical performance. Natural fiber-based composites have emerged as promising alternatives in civil engineering applications due to their renewability, biodegradability, low density, and favorable strength-to-weight ratios [16,17,18]. Fibers such as jute, flax, sisal, and coir have been successfully employed in geotextiles, erosion control mats, and soil reinforcement systems, where their tensile capacity and interaction with soil are mobilized primarily under static or quasi-static loading conditions [19,20,21].

Among natural fibers, coir—extracted from the husk of coconuts—offers distinct advantages for outdoor and geotechnical applications. Coir fibers exhibit a comparatively high tensile strength, large elongation at failure, and superior resistance to biological degradation when compared with other lignocellulosic fibers [22,23,24]. Their coarse texture and durability make them particularly suitable for applications involving mechanical interlocking and repeated loading. Consequently, coir-based geotextiles have been widely used for erosion control, slope stabilization, and vegetation support [19,25]. The existing woven coir geotextile (700 gsm) commonly used in erosion control applications is shown in Figure 1.

Despite these advantages, the application of coir geotextiles has largely been limited to low-energy or serviceability-driven applications. Their potential use as load-bearing or impact-resistant components in flexible barrier systems remains insufficiently explored. Experimental data describing the behavior of coir-based barriers under impact loading conditions representative of debris flows or rockfalls are scarce. The absence of such data constrains the development of rational design methodologies and performance-based classification frameworks for natural fiber barrier systems [12,26].

From a materials perspective, a woven coir geotextile barrier may be considered a natural fiber composite system in which load transfer arises from the interaction between coir ropes arranged in warp and weft directions, their interconnections, and boundary support conditions. Under static and dynamic loading, stresses are redistributed through tensile mobilization of individual ropes, friction at rope intersections, and deformation compatibility across the barrier system [14,23]. Understanding this composite response is essential for assessing the feasibility of replacing conventional steel meshes with natural fiber alternatives in selected hazard mitigation scenarios.

Durability is another critical factor governing the performance of natural fiber composite systems. Exposure to ultraviolet radiation, moisture, temperature variations, and cyclic wetting and drying can lead to progressive degradation of mechanical properties [16,17]. Accelerated weathering techniques provide an effective means of simulating long-term environmental exposure within laboratory timescales and have been widely adopted to evaluate the residual strength and service life implications of geotextiles and fiber-reinforced composites [25,27]. However, the durability of coir-based barrier systems under combined mechanical and environmental loading conditions remains inadequately quantified, necessitating systematic experimental investigation [25,28,29,30,31].

Recent advances in natural fiber-reinforced polymer composites have significantly expanded their applicability beyond low-load civil engineering uses and into semi-structural and impact-resistant domains. Comprehensive reviews have demonstrated that plant fiber composites can achieve competitive strength-to-weight ratios, improved energy absorption, and enhanced sustainability when appropriate fiber treatments, hybridization strategies, and optimized fabrication techniques are employed [32,33,34]. Life cycle assessments further confirm that natural fiber composites can achieve substantial reductions in embodied energy and carbon emissions compared with conventional synthetic composites, strengthening their suitability for infrastructure and transportation applications where environmental impact is a key consideration [35,36].

In this context, the present study investigates the feasibility of using a coir geotextile composite barrier as a sustainable alternative to steel mesh in flexible landslide mitigation systems. The study focuses on the development of a high-strength woven coir geotextile barrier fabricated using multi-strand coir ropes and examines its mechanical, degradation, and impact resistance characteristics through a comprehensive experimental program. Static loading, impact loading using vertical drop tests, and sustained load retention behavior are investigated to assess structural performance under representative service conditions. The schematic representation of the steel mesh flexible landslide barrier and the proposed coir geotextile composite barrier is shown in Figure 2. The novelty of this work lies in treating the coir geotextile barrier as a functional composite system designed for energy dissipation and load redistribution under impact conditions rather than as a conventional erosion control product. By systematically examining the influence of the rope configuration, connection density, and loading conditions on barrier behavior, this study contributes experimental evidence toward the development of sustainable natural fiber composite barriers for landslide mitigation applications. While previous studies on coir fibers and coir-based geotextiles have largely focused on erosion control, slope stabilization, and soil reinforcement, the present study uniquely investigates a woven coir geotextile barrier at the barrier system scale, with explicit evaluation of the mechanical response, impact resistance, and post-impact load retention through large-scale physical testing.

Several recent studies have explored the impact and energy absorption characteristics of natural fiber composites under dynamic loading conditions. Investigations into ballistic and low-velocity impact behavior have shown that the fiber architecture, interface quality, and composite thickness play a critical role in governing damage tolerance and post-impact integrity [37,38]. In addition, advances in multifunctional natural fiber composites incorporating sensing, damage monitoring, and energy-efficient manufacturing have highlighted the potential for integrating performance monitoring with sustainable materials [39,40,41]. However, despite these advancements, experimental studies focusing on natural fiber-based flexible barrier systems subjected to impact loading representative of debris flow or rockfall conditions remain limited, particularly for coir-based woven geotextile barriers.

2. Materials and Barrier Development

2.1. Coir Fiber and Rope as Composite Constituents

Coir fiber is a lignocellulosic natural fiber extracted from the outer husk of coconuts and is widely recognized for its relatively high tensile strength, large elongation at failure, and resistance to biological degradation when compared with other plant fibers such as jute or flax [17,22,23]. These characteristics make coir particularly suitable for applications involving tensile load transfer, mechanical interlocking, and exposure to outdoor environments. In geotechnical engineering, coir fibers are commonly processed into ropes, yarns, and woven geotextiles, which are used for erosion control, slope stabilization, and soil reinforcement [19,24,25].

For barrier applications, the load-bearing capability of the system is governed not by individual fibers but by the collective behavior of bundled fibers assembled into ropes and subsequently woven into a planar structure. From a composite material perspective, coir ropes act as unidirectional tensile elements, while their interlacing within a woven configuration enables load redistribution across multiple load paths. The mechanical response of such a system depends on the fiber properties, strand configuration, rope diameter, and interaction between intersecting elements under load [14,23].

In the present study, coir fibers sourced from mature coconut husks were processed into ropes with different strand configurations. The rope manufacturing process involved twisting individual fiber bundles into strands, which were then combined to form multi-strand ropes. Increasing the number of strands enhances the effective cross-sectional area and improves load sharing among fibers, thereby increasing the tensile capacity and deformation tolerance. This approach allows tailoring of mechanical performance while maintaining the inherent flexibility required for barrier systems.

2.2. Selection of Rope Configuration and Strand Geometry

Selecting an appropriate rope configuration is a crucial step in developing a coir geotextile composite barrier. Conventional coir geotextiles used for erosion control typically employ ropes with low strand counts, resulting in a relatively low mass per unit area and limited tensile capacity. Such configurations are inadequate for applications involving impact or sustained loading.

To address this limitation, coir ropes with higher strand counts were investigated. Rope configurations with increasing numbers of strands were examined to assess the impact of strand geometry on tensile behavior and workability. As the strand count increases, the rope exhibits enhanced tensile strength and a greater elongation capacity due to improved stress redistribution among the fibers [20,23]. At the same time, excessive stiffness or handling difficulty must be avoided to ensure practical manufacturability and field installation.

Based on these considerations, a multi-strand rope configuration was selected that provided an optimal balance between strength, flexibility, and ease of fabrication. This configuration enabled efficient weaving into a planar geotextile while maintaining sufficient tensile resistance for barrier applications. The selected rope geometry also allowed compatibility with conventional coir-processing equipment, supporting scalability and potential field implementation. A view of coir ropes with different strand configurations is shown in Figure 3.

2.3. Weaving Architecture and Composite Action of the Geotextile Barrier

The coir geotextile barrier was developed by weaving the selected multi-strand coir ropes into a planar grid structure. The weaving architecture follows a warp-weft arrangement, where longitudinal ropes (warp) provide the primary load-carrying capacity and transverse ropes (weft) ensure dimensional stability and load redistribution across the barrier width. A schematic representation of the weaving pattern is shown in Figure 4. At the intersections, frictional resistance and rope interlocking contribute to the overall composite action of the system. From a structural standpoint, the woven geotextile behaves as a flexible tensile membrane rather than a rigid panel. Under loading, forces are transferred through the tensile mobilization of the ropes, the progressive engagement of connections, and the redistribution of stresses across adjacent elements. This behavior is analogous to that of conventional steel mesh barriers, where energy dissipation occurs through large deformations and controlled load transfer rather than through rigid resistance [7,8,12].

The aperture size of the woven structure was selected to ensure an appropriate balance between mechanical performance and functional requirements. Larger apertures facilitate drainage and reduce hydrostatic pressure build-up, while smaller apertures improve load interception and debris retention. The chosen weaving pattern ensured uniform aperture distribution and consistent mechanical response across the barrier surface.

2.4. Geometry and Fabrication of the Coir Geotextile Composite Barrier

The dimensions of the coir geotextile composite barrier were selected to be comparable with those of flexible steel mesh barriers commonly adopted in practice. The barrier was fabricated as a rectangular panel with a predefined length and width (4 m × 2 m), enabling a direct comparison of performance under similar boundary conditions. The ropes were woven manually using a controlled process to ensure consistent spacing, alignment, and tension across the barrier.

Edge reinforcement was provided by looping the terminal ropes to facilitate connection with supporting cables and anchorage systems during the testing process. These connections play a critical role in governing the overall performance of flexible barriers, as load concentration and failure often initiate at connection points rather than within the mesh itself [8,9]. Accordingly, the fabrication process ensured that rope ends were securely integrated into the barrier geometry to minimize premature slippage or rupture. The manufacturing process and the developed coir geotextile composite barrier are shown in Figure 5.

The resulting coir geotextile barrier can be regarded as a natural fiber composite system, where the mechanical response arises from the combined behavior of the rope elements, their interactions at intersections, and the boundary constraints imposed by the support system. This composite interpretation forms the basis for the experimental investigations described in subsequent sections.

3. Experimental Program

The experimental program was designed to evaluate the mechanical behavior, durability, and impact resistance of the developed coir geotextile composite barrier under loading conditions representative of landslide and debris flow mitigation scenarios. Prior to testing, all coir ropes were visually inspected to ensure a uniform diameter, intact strands, and the absence of visible defects. The woven geotextile barrier specimens were fabricated using identical weaving procedures and connection detailing to ensure consistency across all large-scale tests. The program comprised four major components: (1) physical characterization of the geotextile barrier, (2) mechanical characterization of coir ropes, (3) accelerated degradation testing, and (4) large-scale loading and impact resistance tests. The experimental sequence was structured to progressively assess the material-level properties, composite behavior, and system-level performance.

3.1. Physical Characterization of the Coir Geotextile Composite

The physical properties of the developed coir geotextile composite barrier were determined in accordance with relevant Indian Standard specifications commonly adopted for geotextile materials. These properties provide essential input parameters for evaluating the barrier’s mechanical performance and functional suitability. The mass per unit area was determined by weighing specimens of known dimensions, as per IS 15868 (Part 1) [42]. Thickness measurements were carried out using a standard thickness gauge under specified normal pressure, as per IS 15868 (Part 2) [42]. The aperture size (mesh opening) was evaluated in accordance with IS 14294 [43], which is particularly relevant for assessing the filtration characteristics and debris retention capability. The overall length and width of the geotextile barrier were measured in accordance with IS 12503 (Parts 1–6) [44]. These measurements were conducted on multiple specimens to ensure repeatability, and the average values were used to represent the physical characteristics of the composite barrier.

3.2. Mechanical Characterization of Coir Ropes

The tensile behavior of coir ropes constitutes a fundamental parameter governing the load-bearing capacity of the geotextile composite barrier. Mechanical characterization was therefore performed on coir ropes with different strand configurations prior to the fabrication of the barrier. Tensile tests were conducted using a universal testing machine (UTM) in accordance with the constant rate of extension (CRE) principle. The testing procedure was carried out in accordance with IS 13162 (Part 5) [45] and IS 1969 [46]. Rope specimens were mounted carefully to avoid slippage or stress concentration at the grips, and loading was applied until failure or until the maximum extension capacity of the testing system was reached. The representative tensile testing set-up using a universal testing machine and testing of 3-strand coir rope and 8-strand coir rope are shown in Figure 6. The tensile force–elongation response was recorded continuously, allowing for evaluation of the peak tensile capacity, elongation behavior, and failure characteristics. The influence of the strand configuration on the tensile response was examined to identify a suitable rope geometry for barrier development.

3.3. Accelerated Degradation Testing

The durability of natural fiber composites under outdoor exposure is a critical consideration for barrier applications. Accelerated degradation testing was conducted to evaluate the impact of environmental exposure on the mechanical properties of the coir ropes used in the geotextile barrier. Physical degradation was simulated using an accelerated weathering chamber designed to replicate the combined effects of ultraviolet (UV) radiation, temperature variation, humidity, and moisture. The exposure protocol was adapted from EN 927-6 [47] and previously reported accelerated weathering studies on geotextiles and fiber-reinforced composites. The test cycle consisted of alternating phases of UV exposure and moisture conditioning, intended to represent long-term outdoor exposure within a shortened laboratory time frame. A view of the coir rope specimens during physical degradation testing is shown in Figure 7. The coir rope specimens were subjected to predefined exposure durations, after which tensile tests were performed using the same procedure described in Section 3.2. The residual tensile strength and stress–strain response were evaluated to quantify degradation-induced changes in mechanical behaviour.

3.4. Large-Scale Loading and Impact Resistance Tests

To evaluate the structural performance of the coir geotextile composite barrier under representative service conditions, large-scale loading and impact resistance tests were conducted. The geometry of the coir geotextile composite barrier, including the overall dimensions, rope spacing, and edge detailing, was kept constant for all tests unless otherwise stated. The boundary conditions were designed to represent the fixed-end support commonly adopted in flexible barrier installations, with edge connections providing load transfer while allowing in-plane deformation of the barrier. These tests were designed with reference to testing concepts adopted for flexible rockfall and debris flow barriers, particularly the principles outlined in ETAG 027 and related experimental studies [26]. A dedicated steel test frame was fabricated to support the geotextile barrier under controlled boundary conditions. The schematic and actual views of the test set-up, along with the instrumentation, are shown in Figure 8. The barrier was mounted within the frame using cable and connection systems that simulate field anchorage. Instrumentation was provided to measure load transfer and barrier response during testing.

Load measurements during the static, impact, and sustained loading tests were recorded using calibrated load cells and tension link transducers connected to a data acquisition system. The data acquisition frequency was selected to adequately capture the peak loads and load–time histories, particularly during impact events. All instrumentation was calibrated prior to testing in accordance with manufacturer specifications. The sequence of loading was carefully controlled to avoid previous damage influencing subsequent tests. Incremental static loading was applied in discrete steps ranging from 50 kg to 550 kg, with a sufficient holding time at each level to allow load stabilization. Impact tests were conducted only after completion of static tests, using drop masses ranging from 50 kg to 550 kg and drop heights between 3 m and 10 m, corresponding to increasing impact energy levels. This progressive loading protocol enabled systematic observation of the barrier response, connection behavior, and failure modes. For the large-scale barrier and impact tests, each loading configuration was investigated under a limited number of test runs due to scale, safety, and logistical constraints; therefore, the reported responses represent the directly measured load–time and deformation histories rather than statistical averages from multiple repetitions.

3.4.1. Incremental Static Load Test

Incremental static load tests were conducted as a preliminary assessment to evaluate the barrier’s ability to withstand sustained loads prior to impact testing. In this test, concrete blocks of increasing weight were placed gradually on the geotextile barrier using a crane system. Each load increment was applied and removed sequentially to observe the deformation behavior and detect any signs of damage or instability. The incremental static load test set-up and deformation behavior of the coir geotextile composite barrier are shown in Figure 9. The static load test provides insight into the stiffness, load redistribution capacity, and minimum load-carrying capability of the composite barrier. It also serves as a screening step to ensure the structural integrity of the barrier before subjecting it to dynamic loading.

3.4.2. Vertical Drop Test for Impact Resistance

Impact resistance was evaluated using a vertical drop test, in which concrete blocks of a specified mass were dropped from predetermined heights onto the center of the geotextile barrier. This test simulates the impact loading experienced by barriers during debris flow or rockfall events.

The drop mass, drop height, and number of barrier connections were systematically varied to assess their influence on the peak impact load and failure behavior. Load measurements were obtained using tension link transducers installed in the supporting cables, and the signals were recorded through a multi-channel data acquisition system. This measurement approach follows the methodologies reported in previous experimental studies on flexible barrier systems [7,8,13]. A view of the vertical drop test set-up is shown in Figure 10.

3.4.3. Load Retention Test Under Sustained Loading

Following impact testing, load retention tests were conducted to evaluate the barrier’s ability to support accumulated debris after an impact event. In this test, a sustained load was applied to the geotextile barrier and maintained for an extended period. Load readings were recorded at regular intervals to monitor any loss of load-carrying capacity or progressive deformation. A view of the load retention test is shown in Figure 11. This test provides critical information on the long-term stability and serviceability of the composite barrier under post-impact conditions, which are often encountered in real debris flow scenarios.

4. Results

4.1. Physical Properties of the Coir Geotextile Composite Barrier

The physical properties of the developed coir geotextile composite barrier using 12-strand rope are summarized in

Table 1. Physical properties of the 12-strand coir geotextile composite barrier.

Physical Property	12-Strand Geotextile Barrier
Mass per unit area	3750 gsm
Thickness	3.6 cm
Aperture size	3.4 cm
Length × width	4 m × 2 m

. The developed coir geotextile composite barrier exhibited a mass per unit area of approximately 3750 g/m², a thickness of 3.6 cm, and a uniform aperture size of about 3.4 cm. These values are substantially higher than those of conventional coir erosion control geotextiles (typically 400–900 g/m²), indicating that the developed system is mechanically more robust and suitable for load-bearing and impact resistance applications. The measured aperture size was uniform across the barrier surface, indicating consistency in the weaving process. These physical characteristics establish the baseline parameters governing the mechanical and hydraulic behavior of the composite barrier and provide essential input for evaluating its structural response under static and dynamic loading.

4.2. Tensile Behavior of Coir Ropes with Different Strand Configurations

The tensile response of coir ropes with different strand configurations is presented in Figure 12. Tensile testing revealed a clear increase in tensile capacity with an increasing strand count (Figure 11). The three-, six-, and eight-strand coir ropes exhibited maximum tensile strengths of approximately 1.2 kN, 1.52 kN, and 2.01 kN, respectively. In contrast, the 12-strand rope did not rupture within the displacement limits of the testing set-up, indicating a significantly higher elongation capacity and tensile resistance (Figure 13). Higher strand configurations displayed a progressive force–elongation response rather than abrupt failure, which is favorable for flexible barrier systems, where controlled deformation is required to dissipate energy. Based on these results, the 12-strand coir rope was selected for barrier fabrication. The ropes with higher strand counts exhibited increased tensile capacities and enhanced elongation behavior. While ropes with lower strand counts reached failure at relatively lower loads, the multi-strand configuration demonstrated a progressive load–elongation response without abrupt failure. The tensile response indicates that increasing the number of strands improves load sharing among fibers, resulting in higher resistance to tensile loading. The absence of brittle failure in higher-strand configurations suggests favorable deformation characteristics for flexible barrier applications, where controlled elongation is desirable.

4.3. Effect of Accelerated Degradation on Mechanical Properties

Accelerated weathering tests demonstrated progressive degradation of the tensile properties with increasing exposure durations (

Table 2. Tensile strength of coir ropes after accelerated weathering exposure.

Type	Test Duration	Max. Stress (MPa)	% Difference	Remarks
12 Strands	0 days	27.9	Nil	No failure observed
12 Strands	32 days	26.4	5.38%	No failure observed
12 Strands	64 days	7.51	73.06%	Failure observed

; Figure 14). After 32 days (equivalent to 3 years of field exposure) of accelerated exposure, the tensile strength reduction in the 12-strand coir rope was limited to approximately 5.4%, with no ruptures observed. However, after 64 days (equivalent to 5 years of field exposure), the tensile strength reduced by approximately 73%, leading to material failure. The stress–strain curves indicate a substantial reduction in stiffness and peak stress after prolonged exposure, highlighting the sensitivity of coir fibers to extended environmental aging. These results suggest that while coir ropes retained an adequate mechanical capacity over short-to-moderate exposure periods, long-term durability becomes a governing factor for sustained applications.

4.4. Static Load-Carrying Capacity Under Incremental Loading

The behavior of the coir geotextile composite barrier under incremental static loading is presented in Figure 15. During incremental static load testing, the coir geotextile composite barrier sustained applied loads ranging from 50 kg to 550 kg. The barrier sustained all applied load increments without rupture or loss of integrity. Deformation increased progressively with the load magnitude, while the overall structural continuity of the barrier was maintained. No visible damage or connection failure was observed during static loading up to the maximum applied load. The load–time response indicates stable load transfer through the composite system, confirming an adequate static load-carrying capacity prior to impact testing.

4.5. Impact Resistance Under Vertical Drop Loading

The results of the vertical drop tests conducted under varying drop masses, drop heights, and connection configurations are summarized in

Table 3. Summary of vertical drop test parameters and observed peak loads.

Test Case	Height (m)	No. of Connections	Drop Weight (kg)	Max. Load (kN)	Remarks
Case 1	10	4	50	6.10	No failure
Case 2	10	4	150	16.97	No failure
Case 3	10	4	250	27.40	2 connections failed
Case 4	10	6	250	23.12	No failure
Case 5	6	6	550	47.56	4 connections failed
Case 6	6	8	550	42.85	2 connections failed
Case 7	6	12	550	43.77	1 connection failed
Case 8	6	16	550	40.38	No failure
Case 9	10	16	550	50.83	No failure

. The representative connection configurations are shown in Figure 16 and Figure 17. The vertical drop tests demonstrated that the peak impact loads increased with the drop mass and height (Figure 18). For a drop height of 10 m, the peak loads increased from approximately 6.1 kN for a 50 kg mass to 27.4 kN for a 250 kg mass when only four connections were provided. Increasing the number of connections for the same drop conditions reduced the peak loads and prevented connection failure. For heavier impacts, a 550-kg mass dropped from 6 m generated peak loads ranging from 47.6 kN (6 connections) to 40.4 kN (16 connections). When the same mass was dropped from 10 m with 16 connections, the peak load increased to approximately 50.8 kN, yet the barrier remained intact. The peak impact loads increased with increasing drop masses and drop heights, while the number of connections significantly influenced the load distribution and failure behavior. Tests conducted with a limited number of connections exhibited connection failure at higher impact energies, whereas configurations with increased connection densities demonstrated improved load redistribution and reduced localized damage (Figure 19). In several test cases, the barrier retained the dropped mass even after partial connection failure.

4.6. Load Retention Behavior Under Sustained Loading

The load retention performance of the coir geotextile composite barrier under sustained loading is shown in Figure 18. Under sustained loading of approximately 1700 kg, the barrier maintained a nearly constant load of 1.74–1.75 kN over a 48-h monitoring period (Figure 20). Only minor fluctuations were observed, with no progressive loss of load-carrying capacity or visible structural damage. This stable response confirms the barrier’s ability to retain accumulated debris following impact events without immediate serviceability loss. The applied load remained nearly constant throughout the monitoring period, with only minor fluctuations observed. No progressive loss of load-carrying capacity or visible damage was detected during the test duration. The time–load response demonstrates the barrier’s ability to maintain structural stability under prolonged loading conditions, which are representative of debris accumulation following impact events.

5. Discussion

5.1. Composite Load Transfer and Energy Dissipation Mechanisms

The ability of the coir geotextile barrier to sustain peak impact loads of up to 50 kN without catastrophic rupture demonstrates that energy dissipation occurs primarily through tensile mobilization of the ropes and large deformation of the composite system (Figure 18). The progressive rise and decay observed in the load–time histories indicate controlled energy absorption rather than brittle failure. Compared with the steel flexible barriers reported in the literature, which typically absorb 7–30% of incoming kinetic energy through deformation, the coir barrier exhibited a qualitatively similar response mechanism, although at lower absolute energy levels. This confirms that natural fiber composites can function effectively as deformable, energy-dissipating systems for moderate hazard scenarios. The experimental results demonstrate that the coir geotextile barrier behaves as a flexible tensile composite system rather than a rigid load-resisting structure. Similar response characteristics have been reported for steel wire mesh and ring net barriers, where only a fraction of the incoming kinetic energy is absorbed by the barrier itself, with the remainder dissipated through deformation and interaction with the impacting mass. The comparable response observed in the coir geotextile barrier highlights the feasibility of natural fiber composites as functional alternatives in selected impact mitigation applications.

5.2. Influence of Connection Density on Structural Performance

The observation that the barriers with 12–16 connections retained their impact on masses of up to 550 kg even after partial connection failure highlights the redundancy inherent in the woven composite system. This progressive failure behavior is a desirable characteristic for protective structures, as it enhances robustness and post-impact functionality. The results from the vertical drop tests show that the barriers with a limited number of connections experienced localized connection failures at higher impact energies, whereas increasing the number of connections improved load redistribution and reduced the extent of damage (Table 3). This behavior can be attributed to the role of connections in controlling load paths and stress concentration. With fewer connections, impact forces are transferred through a limited number of load-bearing elements, resulting in higher local stresses and a higher likelihood of premature connection failure. Increasing the connection density distributes the applied load across a larger number of tensile elements, thereby reducing the peak stresses and enhancing the overall system’s resilience. This finding is consistent with observations from full-scale testing of steel flexible barriers, where the connection configuration and anchor layout have a strong influence on system performance and residual capacity.

5.3. Static Load Capacity and Post-Impact Stability

The barrier’s ability to sustain static loads up to 550 kg without damage and retain 1700 kg under sustained loading for 48 h indicates that tensile creep and time-dependent deformation were limited over the test’s duration (Table 3, Figure 11 and Figure 18). This suggests that the developed composite barrier can maintain post-impact stability under debris accumulation conditions commonly encountered in shallow landslide events. The incremental static load tests confirmed that the coir geotextile composite barrier possesses sufficient stiffness and strength to withstand sustained loads prior to impact events (Figure 15). The absence of visible damage or ruptures under maximum applied static loads indicates stable load transfer through the woven rope network. Together, these observations indicate that the developed coir geotextile barrier satisfies both the impact resistance and post-impact serviceability requirements, which are essential performance criteria for flexible mitigation systems.

5.4. Durability and Implications of Degradation Behavior

The degradation results reveal a clear threshold behavior. Tensile strength loss was limited to 5% after short-term exposure but exceeded 70% after prolonged accelerated weathering. This trend is consistent with previous studies on natural fiber composites and geotextiles, which have shown that ultraviolet radiation and moisture exposure accelerate fiber degradation and reduce the load-bearing capacity [16,17,25]. This indicates that environmental aging, rather than the immediate mechanical capacity, governs the long-term performance of coir-based systems. From a design perspective, this suggests that coir geotextile barriers are best suited for temporary to semi-permanent mitigation measures unless protective treatments or hybrid reinforcement strategies are adopted to extend the service life [18,34]. From a practical perspective, these findings suggest that coir geotextile barriers are well suited for applications where service life requirements align with the degradation characteristics of natural fibers. For temporary or semi-permanent mitigation measures, such as protection during construction phases, post-failure stabilization, or low-frequency hazard zones, the observed durability may be adequate [19,24]. In contrast, long-term applications may require additional protective measures, such as surface treatments, hybridization with synthetic fibers, or periodic replacement strategies [32,33]. In the present study, accelerated aging tests were conducted not to predict an exact service life but to identify the performance thresholds beyond which the mechanical capacity of the coir geotextile composite barrier becomes unacceptable for structural use. The observed transition from limited strength reduction during early exposure to rapid degradation at extended aging durations defines a clear durability-based performance boundary that can be used to establish acceptable service duration and replacement strategies in design.

5.5. Comparison with Conventional Steel Mesh Barriers

While steel mesh barriers offer high tensile strength and long-term durability, they are associated with high embodied energy, corrosion susceptibility, and an environmental impact. The coir geotextile composite barrier investigated in this study demonstrates several functional similarities to steel-based systems, including flexible load response, energy dissipation through deformation, and redundancy through multiple load paths. Although the absolute tensile capacity of coir ropes is lower than that of steel wires, the composite action of the woven system and the ability to tailor the connection density enable the barrier to achieve meaningful impact resistance for small-to-moderate hazard scenarios. In addition, the lower stiffness of coir ropes contributes to reduced peak impact forces, which may be advantageous in limiting anchor loads and foundation demands. The results indicate that coir geotextile composite barriers should not be viewed as direct replacements for high-energy steel systems but rather as sustainable alternatives for specific applications where environmental considerations, ease of installation, and moderate performance requirements are prioritized.

5.6. Engineering Significance and Practical Implications

The findings of this study highlight the potential of natural fiber composite systems to extend beyond conventional low-energy geotechnical applications into impact mitigation roles. By demonstrating that a woven coir geotextile barrier can resist static loads, dissipate impact energy, and retain debris under sustained loading, this work provides experimental evidence supporting its practical feasibility. From an engineering standpoint, the ability to tune performance through the rope configuration and connection density offers flexibility in design and adaptation to site-specific hazard conditions. In addition to technical feasibility, practical deployment considerations were taken into account in defining the scope of this study. The proposed coir geotextile composite barrier is based on commercially available coir ropes and conventional weaving techniques, and it is therefore intended as a market-ready solution for small-to-moderate hazard scenarios, where ease of installation, sustainability, and a controlled service duration are prioritized. Moreover, the use of locally available and renewable materials aligns with sustainable infrastructure development goals and may provide cost-effective solutions in regions where conventional steel systems are economically or logistically challenging.

6. Conclusions

This study evaluated the feasibility of using a coir geotextile composite barrier as a sustainable alternative to conventional steel mesh systems for landslide mitigation through a comprehensive experimental investigation of the mechanical behavior, degradation characteristics, and impact resistance. Based on the experimental findings, the following conclusions are drawn:

• A woven coir geotextile composite barrier fabricated using multi-strand coir ropes exhibited a high mass per unit area (3750 g/m²) and maintained structural integrity at full scale, demonstrating its suitability for load-bearing barrier applications.
• Tensile characterization of coir ropes indicated that increasing the strand count significantly enhanced mechanical performance. The multi-strand configurations achieved tensile capacities exceeding 2 kN and exhibited large elongation values without abrupt ruptures, indicating deformation-tolerant behavior that is advantageous for flexible, energy-dissipating barrier systems.
• Accelerated degradation tests revealed a limited reduction in tensile strength of approximately 5% after short-term exposure, whereas prolonged exposure resulted in strength losses exceeding 70%. The accelerated aging results are therefore interpreted as defining the durability-controlled performance limits of the barrier system, providing a rational basis for determining safe operational windows.
• Incremental static load tests confirmed that the developed barrier could sustain loads of up to 550 kg without rupture or loss of structural continuity. In addition, sustained loading of approximately 1700 kg was maintained over a period of 48 h with a negligible loss in load-carrying capacity, indicating satisfactory post-impact serviceability.
• Vertical drop impact tests demonstrated that the coir geotextile composite barrier was capable of resisting peak impact loads ranging from approximately 6 to 51 kN, depending on the drop mass, drop height, and connection configuration. Increasing the connection density significantly improved load redistribution, reduced localized damage, and enabled the barrier to retain impacting masses even after partial connection failure.

Overall, the results demonstrate that woven coir geotextile composite barriers can function as flexible, energy-dissipating systems capable of mitigating small-to-moderate landslide and debris flow impacts. While these barriers are not intended to replace high-energy steel protection systems, they offer a viable and environmentally sustainable alternative for applications where moderate performance requirements, ease of installation, and reduced environmental impact are prioritized.

Despite establishing the structural feasibility of coir geotextile composite barriers under controlled laboratory conditions, certain limitations should be acknowledged. The impact response was evaluated using vertical drop tests, which do not fully capture the complex flow–structure interactions associated with real debris flows. Furthermore, durability assessment was limited to accelerated physical weathering, and other degradation mechanisms such as biological activity, abrasion, and long-term creep were not explicitly considered. Future research should therefore focus on large-scale flume testing, advanced numerical modeling incorporating large deformations, and field-scale trials to establish comprehensive performance envelopes and realistic service life expectations under in situ environmental conditions.