Novel Ropes from Textile Waste and Polypropylene Nonwoven for Dual-Function Use in Slope Erosion Control and Retaining Structures

Abstract

The use of waste textiles and the search for alternative materials for landslide and erosion control are currently subjects of great importance. This paper presents and evaluates a novel application of waste wool and waste textile ropes arranged in a rhomboid pattern on a slope, and polypropylene nonwoven ropes threaded through iron rods to form a layered retaining wall at the slope toe. Together, these measures provide dual functionality in erosion control and the retaining wall. Monitoring results, material property evaluations, and qualitative and quantitative erosion assessments using the Universal Soil Loss Equation model indicate that the proposed measures are effective, with both the slope and the retaining wall performing well several years after installation. Furthermore, variations in the rainfall erosivity factor as calculated using different equations can lead to notable differences in estimated soil loss, highlighting the need for careful determination of this factor. This case demonstrates a new approach to using polypropylene nonwoven material, and potentially also waste textiles, as a layered retaining structure that is cost-effective and time-efficient and contributes to sustainability and the circular economy. Similar layered retaining structures could be applied in various fields of civil and environmental engineering.

1. Introduction

Every year, 12.6 million tonnes of textile waste are generated in the EU. Clothing and footwear alone account for 5.2 million tonnes of this waste, equivalent to 12 kg of waste per person annually [1]. Therefore, the EU objectives aiming to promote sustainability from a circular economy perspective include reductions in the use of raw materials, recovery and recycling strategies to reduce waste generation, and changes in consumer and business behaviours [2].

Globally, it is estimated that less than 1% of all textiles are recycled into new products [1]. According to [3], assuming current solid waste generation during production and at end of use, fashion waste is projected to increase by about 60% between 2015 and 2030, with an additional 57 million tonnes of waste generated annually. This will bring the total amount of fashion waste in 2030 to 148 million tonnes—equivalent to an annual waste of 17.5 kg per capita worldwide. The vast majority of clothing waste ends up in landfills or is incinerated; globally, only 20% of clothing is collected for reuse or recycling.

Therefore, many researchers are investigating ways to utilize textile waste materials across various sectors, including the construction industry, geotechnical engineering, and environmental engineering.

Regarding the use of textile waste in the construction industry, textile waste improves the properties of concrete [4], cement composites [5], and pervious concrete [6], and the thermal properties of building components [7]. Wool waste can be used as a new raw material suitable for building components [8] or in environmental engineering as a soil additive, making it suitable for the germination and growth of plants used for slope protection [9,10].

Textile waste can also be utilized thanks to Kemafil technology, which produces ropes of various diameters from textile waste [11]. Ropes manufactured using this technology have been successfully applied for slope protection against erosion on artificially created terrace [12], remediation of damaged ditch slope [13], protection of road slope against erosion [14], and reclamation of abandoned open mine slopes [15,16]. In all cases, ropes are installed parallel to the base of the slope in a meandering pattern (length 1.8 m, width 0.5 m). These cases differed not only in soil properties but also in climatic and hydrogeological conditions and slope angles. However, in no case did water flow from beneath the slope; it flowed only along the slope’s surface.

The authors of [17] reviewed 49 studies from 1986 to 2020 focusing on novel applications of textile waste in the construction industry and geotechnical engineering. They presented numerous innovative strategies for the cascading use of textile fibrous waste by transforming it into nonhazardous secondary raw materials for potential environmentally friendly and cleaner applications in the fields of building materials and geotechnical engineering. Two of the studies mentioned are co-authored by the authors of this paper. In these studies, ropes made from textile waste were successfully applied, but they were used, in a method similar to previous cases, under relatively simple hydrogeological conditions (water flowed only on the slope’s surface, not from beneath the slope). It is desirable to test the application of textile waste ropes under more complex hydrogeological conditions as well (e.g., in flysch mountain areas, where water flows from beneath the slope).

The Universal Soil Loss Equation model (USLE) [18] is often applied to demonstrate the effectiveness of various applications against erosion.

Since the parameters used in USLE modelling are strongly dependent on geographical features, there are many publications dealing with the application of USLE modelling for conditions in Poland. Unfortunately, Polish authors propose various methods to obtain values for particular USLE parameters.

According to [19], rainfall erosivity for a single rainfall occurrence is calculated as the sum of the rain kinetic energy and its maximum 30 min intensity. The annual sum of these values forms the R_r factor. For modelling purposes, this value equals the mean value in recent years. Detailed meteorological data are required to assess the R_r factor, but the limited number of stations in Poland and worldwide has made it necessary to seek alternative methods for estimating R_r factor values. Such a method should be based on data gathered regularly in measurement stations or on correlation with other easily accessible data.

Among the rainfall erosivity factor estimation methods based on precipitation data, the modified Fournier index is the most commonly applied [20]:

$$R_r=F=\sum _{i=1}^{12}{\displaystyle \frac{p_i^2}{P}},$$

(1)

where pi is the monthly precipitation total in i-th month (mm), and P is the annual precipitation total (mm). Formula (1) is applied in the analysis of water erosion within the Dobczyce reservoir [21].

Research on the applicability of monthly rainfall data in estimating the R_r factor in Poland was conducted by Licznar [22]. He concluded that the best results in estimating the annual erosivity rainfall factor in Poland were obtained by using a modified Fournier index with an exponent correlation, as follows [19]:

$$R_r=0.226·F^{1.2876}.$$

(2)

In [23], the author states that there are strong relationships between elevation, total annual precipitation, and average annual rainfall erosivity factor values in a Polish database of 67 gauging stations:

$$R_r=0.0519·H+40.89,$$

(3)

$$R_r=0.0819·P-0.9838,$$

(4)

where: Rr—Average annual rainfall erosivity factor (MJ·ha⁻¹·cm·h⁻¹);

H—Elevation above sea level (m);

P—Total annual precipitation (mm).

Licznar [24] also published an analysis of local annual R_r factor values for 103 stations in Poland. Calculations were made by means of single hidden layer perceptron artificial neural network on the base of monthly precipitation totals from the years 1961–1980. For most of the analyzed stations, the calculated average annual R_r factor values were low or moderate, ranging from 50 to 80 (MJ·cm·ha⁻¹·h⁻¹·y⁻¹). A strong relation (R² = 0.7837) between calculated average annual factor values and station elevation above sea level was observed:

$$R_r=0.0709·h+49.246.$$

(5)

Regarding the use of geosynthetics in retaining structures, they primarily act as reinforcement elements in mechanically stabilized earth walls, where geotextiles or geogrids are placed in horizontal layers within the backfill. The wall facing can be precast panels, gabions, or wrapped geosynthetic faces.

The author of [25] presented the Texsol structure and demonstrated that the reinforcement of sand by continuous polyester fiber provides the composite material with apparent cohesion, the ability to sustain large strains, and high energy-absorption capacity, making Texsol structures a cost-effective solution for highway retaining systems. This composite material is used to create a wall facing.

The authors of this article have no knowledge of any case where geotextiles form the retaining structure itself.

Although waste wool and textile ropes have been successfully applied in many cases, they have not yet been used in more demanding hydrogeological conditions, especially on slopes in flysch areas, where water flows not only along the slope but also beneath it. In such cases, not only is the slope itself critical, but also the slope toe, the failure of which can trigger further chain failures of the slope upwards. Therefore, the goal of this study is to present and comprehensively evaluate a novel dual application: a combination of waste wool and textile ropes arranged in a rhomboid pattern for slope protection, and a layered retaining structure created from polypropylene nonwoven ropes for toe stabilization. We demonstrate the effectiveness of these measures through long-term in situ monitoring, material property assessment, and qualitative and quantitative erosion evaluation using the USLE model. This case study shows that this innovative structure, leveraging the principles of the circular economy, represents a functional and promising alternative to traditional techniques, with potential application across a wide range of civil and environmental engineering projects.

2. Materials and Methods

2.1. Site Characteristics and Sampling

The experimental slope requiring stabilization is a road-cut slope in Sobolówka, municipality of Ujsoły, Żywiec District, Silesian Voivodeship, southern Poland (49°25′48.35″ N, 19°4′27.16″ E), along a forest road connecting the villages of Rycerka Górna and Ujsoły.

This location is characterized by the flysch belt formed mainly during the Late Cretaceous to Paleogene in the Carpathian Foredeep basin (Bystrica subunits of the Magura Nappe, External Western Carpathians). The location is displayed in the sheet Ujsoły (1046) of the detailed geological map of Poland, scale 1:50,000 [26]. As reported by the forestry staff, landslides frequently occur along the road cut in this section, after which the displaced material is removed and the landslides recur. It is therefore assumed that, if no slope stabilization method is implemented, the landslides will gradually increase in scale, endangering the upper part of the slope.

No engineering geological report and no investigation points or boreholes are registered in the Polish Central Geological Database for the experimental location. According to the knowledge gained during field surveys, the soils of the subject landslide can be classified as unclassified Quaternary rocks (according to [26]), which are clays, sands, and rock debris— deluvial and congelifluctional, that cannot be distinguished. These are mainly clay and clayey sediments containing a large admixture of debris material. Depending on the bedrock structure, they consist of sandy clays with debris or pure clay–sand material. They exhibit a characteristic arrangement of debris material, with the longer axis aligned with the slope gradient. They occur in all valleys on the studied sheet (Ujsoły (1046)), with their thickness and area of occurrence increasing downstream along the river valleys. Clays and clays with rock debris, as well as blocks (flysch packages), are colluvial. These deposits are composed of colluvial material from various types of landslides, rockfalls, and slides of weathered material, of which there are approximately 100 in the area of the studied sheet Ujsoły (1046) [26].

A closer view of the slope on 08 June 2018 and the soil sample locations can be seen in Figure 1.

Installation of the ropes on the slope and in the wall was carried out on 5–6 October 2018. First, a roughly 0.15 m layer of topsoil (the first 3 m from the left side) and 0.10 m (the remaining 7 m) on slope 1 was removed (a total of about 7.5 m³ of soil) and placed on the road surface using a backhoe loader. This soil was then mixed with 150 kg of waste wool (about 1% of the dried soil mass) and compacted back onto the slope with the installed ropes. To stabilize the slope, ropes made from strips of wool stitch-bonded nonwoven (wool rope), strips of stitch-bonded nonwoven from a mixture of recycled natural and synthetic fibers (RNSF rope), and strips of polypropylene nonwoven (PP rope) were applied. The wool and RNSF ropes have diameters of about 8 cm, while the PP rope has a diameter of about 5 cm. The material properties are presented in

Table 1. Material properties.

Parameters	Standard Descriptive Statistics	Wool	RNSF	PP
Mass per square meter	$\overline{\mathrm{x}}$ (g/m2)	322.0	265.0	168.3
	SD (g/m2)	15.3	12.5	10.34
	CV (%)	4.8	4.7	6.14
Thickness	$\overline{\mathrm{x}}$ (mm)	2.90	3.03	1.90
	SD (mm)	0.10	0.20	0.16
	CV (%)	3.0	5.4	8.50
Machine direction tension strength	$\overline{\mathrm{x}}$ (kN/m)	5.01	3.80	3.03
	SD (kN/m)	0.30	0.19	0.5
	CV (%)	5.4	4.91	16
Machine direction elongation at break	$\overline{\mathrm{x}}$ (%)	42.42	35.20	35.67
	SD (%)	2.1	2.5	1.2
	CV (%)	4.9	7.1	3.5
Cross direction tension strength	$\overline{\mathrm{x}}$ (kN/m)	0.40	0.90	2.72
	SD (kN/m)	0.06	0.07	0.5
	CV (%)	15.4	17.9	16.6
Cross direction elongation at break	$\overline{\mathrm{x}}$ (%)	80.00	74.20	98.50
	SD (%)	5.3	5.2	8.9
	CV (%)	6.7	7.0	9.0

. The thickness, mass per square meter, and tensile strength and elongation at break of the fabrics were determined in accordance with relevant standards [27,28,29].

Wool ropes were installed in a rhomboid pattern on the left 6 m of the slope, measured at the slope toe (i.e., the left 6 m of the wall). RNSF ropes were installed in a rhomboid pattern on the right 4 m of the slope (i.e., the right 4 m of the wall). At the intersections of the ropes, plastic zip ties were used to secure the ropes together, along with steel rebar rods with a diameter of 8 mm and a length of 80 cm, of which 65 cm was embedded into the ground to prevent the ropes from sliding down the slope. At the slope toe, two rows of steel rods with a diameter of 12 mm and a length of 1 m were installed, of which 50 cm was embedded into the ground, with the rows spaced 8 cm apart. Within each row, the rods were spaced 0.5 m apart, and the rods in the second row were offset by 0.25 m relative to the rods in the first row. After the installation of the ropes on the slope and in the wall, the slope and the area behind the wall were backfilled with soil mixed with waste wool, and subsequently, a grass-based anti-erosion mixture (2.7 kg) was sown on the soil surface at a rate of about 40 g·m⁻². Details of rope installation on 6 October 2018 can be seen in Figure 2.

After installation, the slope and wall were monitored. After 65 months, a site visit took place on 4 March 2024 and 6 March 2024, during which four soil samples were taken (samples 5 and 6 from the slope; samples 7 and 8 from the holes located just behind the wall). Details on soil and rope sampling can be seen in Figure 3.

2.2. Soil Analyses and Rope Properties

Determinations of soil particle size distribution, water content (w), liquid limits (w_L), and plastic limits (w_P) were carried out in accordance with the Polish standard PN-88/B-04481 [30] (with an exception in sieve sizes; instead of 40 mm, 25 mm, and 10 mm, the following were used: 63 mm, 31.5 mm, 16 mm, 8 mm, and 4 mm). Soil classifications were performed based on the obtained values in accordance with the Polish standard [31] and ISO [32]. Further soil parameters, such as the plasticity index (I_P), consistency index (I_C), and liquidity index (I_L), were calculated using well-known formulas in soil mechanics. Knowing the soil classification and the liquidity index (I_L), soil unit weights and soil shear strength parameters were determined according to method B in the Polish standard PN-81/B-03020 [33]. The formulas presented in [34] were applied instead of the diagram in [33].

Sixty-five months after rope installation (this research), the mechanical parameters of the nonwovens were measured. The measurements of tensile strength and elongation at break were carried out in accordance with the Polish standard [29] using a H50K-S Hounsfield tensile machine (Hounsfield Test Equipment Ltd., Redhill, UK). The design tensile strength of the wool ropes was obtained by multiplying the tensile strength [kN·m⁻¹] by 1.5 m (width of nonwoven used for production of ropes with a diameter of 8 cm) and dividing by 1.1 (proposed reinforcement material factor), and the design tensile strength of the RNSF ropes was obtained by multiplying the tensile strength [kN·m⁻¹] by 1.8 m (width of nonwoven used for production of ropes with a diameter of 8 cm) and dividing by 1.1 (proposed reinforcement material factor). The design tensile strength of the PP ropes was obtained by multiplying the tensile strength [kN·m⁻¹] by 1.5 m (width of nonwoven used for production of ropes with a diameter of 5 cm) and dividing by 1.1 (proposed reinforcement material factor). The morphology of the fibers was investigated by scanning electron microscopy (SEM). A JEOL JSM 5500 LV microscope (JEOL Ltd., Tokyo, Japan) operating in the backscattered electron mode was used. Observations were carried out for fibers sputtered with gold using a JEOL JFC 1200 ionic sputter.

2.3. Determination of the Soil Load on the Rope

Soil load on the ropes will be determined using well-known methods in geotechnical engineering (slope stability, soil pressure). To determine the tension loads induced in the ropes by the soil load, the calculation procedure outlined in [16] will be applied.

According to [35], for extensible reinforcement, the tension force $T_{rp}$ per running meter, generated in the reinforcement from vertical loading $W_T$, is

$$T_{rp}={\displaystyle \frac{W_T·\left(s-a\right)}{2·a}}·\sqrt{1+{\displaystyle \frac{1}{6·\mathrm{\epsilon }}}},$$

(6)

where (see Figure 4), $T_{rp}$ is the tension force in the reinforcement (kN), $W_T$ is the vertical loading acting on the reinforcement between two adjacent pile caps (kN), $s$ is the distance between the adjacent piles (m) (in our case, the distance between steel rebar rods on the slope, which is 0.5 m, and the distance between steel rebar rods in the wall, which is also 0.5 m), $a$ is the size of the pile cap (m) (in our case, we propose 0.08 m), and $\epsilon$ is the strain in the reinforcement (-), which was calculated based on the real rope length and distances $s$. This equation for $T_{rp}$ is suitable for these reinforcements, which can undergo deformation during loading, meaning extensible reinforcements (e.g., polymeric). In this case, the aforementioned calculated real values of $\epsilon$ were applied.

The load $W_T$ acting on the rope placed on the slope (at the location where soil specimens No. 5 and 6 were taken) was calculated as the difference between the active force (the tangent component of the soil weight, buoyant force, and the force from flowing water) and the passive force (friction and cohesion forces on the sliding surface) using well-known formulas in geotechnical engineering (see the ropes in the rhomboid in Figure 5). The force W_T acting perpendicular to the rope is calculated using the following formula:

$$W_T=\left(G.sin\alpha +J_w-\left(\left(G.cos\alpha -W\right)·\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{\phi }+\mathrm{A}·\mathrm{c}\right)\right)·\mathrm{c}\mathrm{o}\mathrm{s}\mathrm{\beta }$$

(7)

where $G$ is half of the soil weight within a single rhomboid (kN), $J_w$ is the force of the flowing water (kN), W is the buoyancy (kN), A is half of the area of the rhomboid (m²), $\mathrm{\phi }$ is the angle of internal friction (°), c is cohesion (kPa), $\alpha$ is slope inclination (°), and $\beta$ is the edge inclination angle of the rhomboid.

Regarding the load $W_T$ acting on the rope placed in the wall (at the location where soil specimens 7 and 8 were taken), it is considered to be equal to the active soil pressure, which can be calculated using well-known formulas in geotechnical engineering. In the case of weakened soil properties (higher $I_L$ values), the sliding force from the slope that must be resisted is added to the earth pressures. Since the earth pressures are greatest at the bottom part of the wall, the loading is evaluated on the lowest reinforcement layer, which is located at a depth of 0.36 m to 0.40 m on the left part (due to soil consolidation behind the wall, the soil thickness behind the wall has decreased from 0.5 m to 0.4 m; the PP rope diameter decreased to 4 cm) and at a depth of 0.31 m to 0.35 m on the right part (for the same reason).

2.4. Qualitative Evaluation of Slope Erosion

To evaluate the effectiveness of the measures presented in the article, a quantitative assessment of slope erosion was carried out, following the USLE modelling [18], as applied in Poland [19]:

$$E_A=R\cdot K\cdot LS\cdot C\cdot P,$$

(8)

where $E_A$ is the mean annual soil erosion rate (actual erosion rate) (t·ha⁻¹·y⁻¹), $R$ is the rainfall and runoff erosivity factor (MJ·cm·ha⁻¹·h⁻¹·y⁻¹), $K$ is the soil erodibility factor (t·h·MJ⁻¹·cm⁻¹), $LS$ is the topographic factor (dimensionless), $C$ is the cover management factor (dimensionless), and $P$ is the erosion control practice factor (dimensionless).

The formula can also be used for the estimation of the potential erosion rate, i.e., the erosion rate from the black fallow without any erosion control practices ($C=1$ and $P=1$). In such a case, the formula simplifies to

$$E_P=R\cdot K\cdot LS,$$

(9)

where $E_P$ is the mean annual soil erosion rate (potential erosion rate) (t·ha⁻¹·y⁻¹).

The rainfall and runoff erosivity factor $R$ is a numerical value that quantifies the long-term average erosive power of rainfall and runoff in a specific geographic area. The authors of [18] state that early spring erosion by runoff from snowmelt, thaw, or light rain on frozen soil may be included in the soil loss computation by adding a subfactor $R_s$ to the location’s erosion index to obtain $R$. In this paper, we also consider the influence of runoff on erosion by adding the subfactor $R_s$, which will be equal to one-tenth of the December through March precipitation [36], so,

$$R=R_r+R_s,$$

(10)

where $R_r$ is the rainfall erosivity factor (MJ·cm·ha⁻¹·h⁻¹·y⁻¹), which will be calculated using the five different formulas (formulas (1) to (5)) presented in Chapter 1, Introduction. $R_s$ is the runoff erosivity factor (MJ·cm·ha⁻¹·h⁻¹·y⁻¹), which will be calculated as one-tenth of the December through March precipitation. To calculate $R_r$ and $R_s$, data on precipitation for these months in the years from 2009 to March 2025 from the rainfall station Oravská Lesná (Slovakia) with station code 11868 (10.7 km from our location) were estimated from the diagrams presented in [37].

The soil erodibility factor $K$ represents the susceptibility of a soil to erosion by water, and is influenced by the soil’s physical properties. The soil erodibility factor $K$ will be calculated in accordance with [18,38]:

$$100\cdot K=2.1\cdot M^{1.14}\cdot {10}^{-4}\cdot \left(12-a\right)+3.25\cdot \left(b-2\right)+2.5\cdot \left(c-3\right),$$

(11)

where $M$: Particle-size parameter, which equals the percentage of the 0.002–0.1 mm fraction multiplied by (100 minus clay percentage).

$a$: Organic matter content (%); if the organic matter content is greater than 4%, then $a=4$.

$b$: Soil structure code used in soil classification (very fine granular: 1, fine granular: 2, medium or coarse granular: 3, and very coarse granular (blocky, platy, or massive): 4).

$c$: Profile saturated hydraulic conductivity code (1, 2, 3, 4, 5, or 6), depending on the value of saturated hydraulic conductivity $K_{sat}$ as follows: rapid: 1 ($K_{sat}\ge 3\cdot {10}^{-5}$ m/s); moderate to rapid: 2 ($3\cdot {10}^{-5}\ge K_{sat}\ge 1.5\cdot {10}^{-5}$ m/s); moderate: 3 ($1.5\cdot {10}^{-5}\ge K_{sat}\ge 4.8\cdot {10}^{-6}$ m/s); slow to moderate: 4 ($4.8\cdot {10}^{-6}\ge K_{sat}\ge 1.2\cdot {10}^{-6}$ m/s); slow: 5 ($1.2\cdot {10}^{-6}\ge K_{sat}\ge 3\cdot {10}^{-7}$ m/s); and very slow: 6 ($K_{sat}\le 3\cdot {10}^{-7}$ m/s). See [36].

According to [39], the values of organic matter content from three samples on slope 2, obtained by the loss-on-ignition method at 800 °C, were 5.79%, 5.95%, and 6.01%, so the average value is 5.91%, which is greater than 4%. It is proposed that values of organic matter content on slope 1, with grass, will also be greater than 4%; therefore, a value of $a=4$ will be considered for all cases.

Based on the grain-size distribution diagram, it can be determined that the soil is medium or coarse granular; therefore, the soil structure code $b=3$ will be utilized for all cases.

According to [38], in cases in which common medium or coarser vertical pores extend through the layer, the saturated hydraulic conductivity $K_{sat}$ will have values from $1\cdot {10}^{-5}$ m/s to $1\cdot {10}^{-4}$ m/s. Taking into account number of clayey and silt particles, the profile saturated hydraulic conductivity code 2 will be used for all profiles (permeability class “moderate to rapid”).

Based on grain-size distribution analysis and [38], the particle-size parameter $M$ and the soil erodibility factor $K_f$ (for fraction up to 2 mm) were calculated using formula (10). The calculation of the soil erodibility factor $K_w$ (for the whole soil) was carried out in accordance with [36], considering the influence of the number of rock fragments on the soil erodibility factor. The obtained values of $K_w$ should be multiplied by 1.313 to obtain $K$ in units of (t·ha·h)/(ha·MJ·cm) [18].

The topographic factor $LS$ combines two features—the slope length factor $L$ and the slope steepness factor $S$. When the slope length $\lambda$ is measured in meters, the $L$ factor value is calculated as follows [18]:

$$L={\left({\displaystyle \frac{\lambda }{22.13}}\right)}^m,$$

(12)

where $\lambda$ is the slope length, and $m$ is the slope length exponent ($m=0.5$ for a steepness of 5% or more; $m=0.4$ for a steepness of 3.5–5%; $m=0.3$ for a steepness of 1–3.5%; $m=0.2$ for a steepness < 1%). In this case, the value $\lambda =7.4$ m will be applied for the slope length. Since the slopes have inclinations of 40° and 45°, the slope steepness will be 83.9% and 100%, respectively; therefore, a value of $m=0.5$ will be applied.

The slope steepness factor S can be calculated using a formula in [18]:

$$S=65.41\cdot {sin}^2\left(q\right)+4.56\cdot sin\left(q\right)+0.065,$$

(13)

where q is the slope steepness (40° and 45°). Topographic factor LS is calculated as LS.

The cover management factor $C$ reflects the effect of cropping and management practices on erosion rates, and it will be determined for conditions in Poland according to the values in

Table 2. Crop types and their C-factor values [40] (italic numbers will be used in this research).

Crop Type	C
Black fallow	1.00
Green fallow	0.01
Winter wheat	0.15
Spring wheat	0.18
Rye	0.15
Winter barley	0.15
Spring barley	0.18
Oats	0.18
Winter wheat–rye	0.15
Spring wheat–rye	0.18
Winter mixed cereal	0.15
Spring mixed cereal	0.18
Maize	0.22
Buckwheat, millet and other cereals	0.18
Potatoes	0.22
Sugar beet	0.22
Winter rape	0.15
Spring rape	0.18
Fodder bulb plants	0.22
Soil-grown vegetables	0.22
Other fodder crops	0.18
Other industrial crops	0.18
Other	0.22

, based on crop type [40]:

The erosion control practice factor $P$ is the ratio of soil loss for a specific support practice to the corresponding loss with up-and-down slope cultivation, and the values of the $P$-factor for parcels cultivated with contour tillage were defined according to the USLE methodology as follows [18]: $P=1$ for slope steepness < 3%; $P=0.5$ for slope steepness 3–8%; $P=0.6$ for slope steepness 8–12%; $P=0.7$ for slope steepness 12–16%; $P=0.8$ for slope steepness 16–20%; $P=0.9$ for slope steepness 20–25%; and $P=1$ for slope steepness > 25%. On other land, a $P$-factor value of 1 was assigned. In this case (other land), a value of $P=1$ will be applied.

According to [19], based on the quantitative evaluation of soil erosion resulting from USLE modelling, a qualitative assessment of erosion risk can be carried out. Based on forecasted soil loss, a location can be assigned to one of six erosion risk classes, with the assumption that the soil degradation level in each particular erosion class should correspond to the grades of erosion intensity introduced by the authors of [40,41] for conditions in Poland (see

Table 3. Erosion classes and soil degradation ([40,41]).

Erosion Class	Erosion Class Description	Soil Degradation
1	No erosion	Does not occur
2	Weak erosion	Small surface-soil loss
3	Moderate erosion	Visible wash-off of humus horizon and deterioration of soil properties; full regeneration of the soil is not always possible through conventional tillage
4	Average erosion	May lead to a total reduction of humus horizon and the development of soils with typologically unformed profiles; terrain dismemberment starts; considerable debris flow into surface waters
5	Strong erosion	Can cause total destruction of the soil profile, including the parent rock; large fragmentation of terrain and deformation of hydrology
6	Very strong erosion	Effects similar to those for strong erosion, but more intensive; a permanent degradation of the ecosystem

).

The classification of actual erosion and the classification of potential erosion can be carried out based on the values of soil loss for each class (

Table 4. Classification of actual erosion [19].

Erosion Class	Erosion Class Description	Erosion Rate (t·ha−1·y−1)
1	No erosion	0–1
2	Weak erosion	1–5
3	Moderate erosion	5–10
4	Average erosion	10–15
5	Strong erosion	15–30
6	Very strong erosion	>30

and

Table 5. Classification of potential erosion [19].

Erosion Class	Erosion Class Description	Erosion Rate (t·ha−1·y−1)
1	No erosion	0–2
2	Weak erosion	2–10
3	Moderate erosion	10–30
4	Average erosion	30–50
5	Strong erosion	50–100
6	Very strong erosion	>100

) [19].

Based on the values obtained for erosion rates for the stabilized slope using the ropes and for the slope without ropes, the erosion class of the slopes will be determined, showing the effectiveness of the proposed measures.

3. Results

3.1. Slope and Wall Condition Monitoring

Slope and wall conditions from installation (6 October 2018) to 20 May 2025 can be seen in Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10. The most important notes are provided in the figure legends.

Concluding this section, it is possible to state that slope and wall condition monitoring showed good slope and wall conditions throughout the entire period. The slope remained stable, even though a new landslide occurred on its left side. The slope on its right side continued to degrade and remained without vegetation cover. The wall made of PP and wool remained vertical, but its height decreased to 0.3 m (on the left side) and 0.35 m (on the right side) due to the consolidation of the soil behind the wall and the related compression of the PP and wool ropes. Nevertheless, it fulfilled and continues to fulfill its function.

3.2. Soil and Rope Properties

Grain-size distribution curves for the soils on the stabilized slope, on the reference slope, and behind the wall can be seen in Figure 11. The soil classifications and properties are given in

Table 6. Soil properties on 17 June 2018 (samples 1–4) and 4 March 2024 (samples 5–8).

Taken on		17 June 2018 (Before Rope Installation)				4 March 2024 (After Rope Installation)
Sample		1	2	3	4	5	6	7	8
Location		Slope 1 (left)	Slope 1 (right)	Slope 2 (upper)	Slope 2 (lower)	Slope 1 (left) (wool rope)	Slope 1 (right) (RNSF rope)	Behind wall (PP rope, left)	Behind wall (PP rope, right)
Grain-size distribution curve number		1	2	3	4	5	6	7	8
Soil classification PN [31]		Żg	Pog	Pog	Pog	Żg	Pog	Żg	Pog
Soil classification ISO [32]		clGr	grclSa	grclSa	grclSa	clGr	grclSa	clGr	grclSa
Liquidity index IL (-)		NA	0.36	0.22	0.30	0.51	0.40	0.49	0.47
Design value of γd (kN·m−3)		20.890	20.890	21.209	21.027	20.549	20.799	20.594	20.640
Design value of φd (°)		11.01	11.01	13.03	11.88	8.856	10.44	9.14	9.43
Design value of cd (kPa)		10.37	10.37	15.04	12.16	6.96	9.32	7.34	7.74
Thickness h (m)		0.20	0.15	0.10	0.10	0.15	0.15	0.40	0.35
Factor of safety Fs (-)		4.73	6.41	13.65	10.99	4.19	5.74	NA	NA
IL = 0.75 (flowing water)	γd (kN·m−3)	20.033	20.003	20.003	20.003	20.033	20.003	20.003	20.003
	φd (°)	5.40	5.40	5.40	5.40	5.40	5.40	5.40	5.40
	cd (kPa)	3.67	3.67	3.67	3.67	3.67	3.67	3.67	3.67
Factor of safety Fs (-)		1.25	1.67	2.45	2.45	1.67	1.67	NA	NA
IL = 1.00 (flowing water)	γd (kN·m−3)	19.434	19.434	19.434	19.434	19.434	19.434	19.434	19.434
	φd (°)	1.80	1.80	1.80	1.80	1.80	1.80	1.80	1.80
	cd (kPa)	1.89	1.89	1.89	1.89	1.89	1.89	1.89	1.89
Factor of safety Fs (-)		0.66	0.87	1.28	1.28	0.87	0.87	NA	NA

Notes: Soil symbols according to [31]: Żg: Żwir gliniasty (loamy gravel); Pog: Pospółka gliniasta (loamy gravel–sand mix). According to [31], the clay fraction has d ≤ 0.002 mm; the silt fraction has 0.002 mm < d ≤ 0.05 mm; the sand fraction has 0.05 mm < d ≤ 2 mm; the gravel fraction has 2 mm < d ≤ 40 mm; and the cobble fraction has d ≥ 40 mm. The liquid limit and plastic limit of sample 1 were not determinable.

and

Table A1. Soil properties on 17 June 2018 (samples 1–4) and 4 March 2024 (samples 5–8).

Taken on		17 June 2018 (Before Rope Installation)				4 March 2024 (After Rope Installation)
Sample		1	2	3	4	5	6	7	8
Location		Slope 1 (left)	Slope 1 (right)	Slope 2 (upper)	Slope 2 (lower)	Slope 1 (left) (wool rope)	Slope 1 (right) (RNSF rope)	Behind wall (PP rope, left)	Behind wall (PP rope, right)
Grain-size distribution curve number		1	2	3	4	5	6	7	8
Soil classification [31]		Żg	Pog	Pog	Pog	Żg	Pog	Żg	Pog
Soil classification [32]		clGr	grclSa	grclSa	grclSa	clGr	grclSa	clGr	grclSa
Clayey fraction (%) [31]		4.9	17.6	22.7	17.2	5.5	6.2	2.6	4.0
Silty fraction (%) [31]		10.0	36.5	40.8	27.0	18.5	19.9	10.6	19.1
Sandy fraction (%) [31]		10.8	17.6	10.8	18.8	22.2	27.2	12.8	21.9
Gravely fraction (%) [31]		67.7	25.5	23.9	33.6	43.8	42.4	68.4	42.8
Cobble fraction (%) [31]		6.6	2.8	1.8	3.4	10.0	4.3	5.6	12.2
Water content (%) [31]		13.8	23.8	23.8	20.9	26.1	26.4	15.7	24.8
Water content for d < 2 mm (%)		37.9	37.9	33.2	37.7	37.1	35.4	36.9	38.9
Plastic limit wP (%) [31]		NA	32.1	29.1	30.3	26.0	26.8	27.5	29.0
Liquid limit wL (%) [31]		NA	50.3	48.3	54.5	48.1	48.4	46.5	50.0
Plasticity index IP (%)		NA	19.1	19.2	24.2	22.1	21.6	19.0	21.0
Consistency index IC (-)		NA	0.64	0.78	0.70	0.49	0.60	0.33	0.52
Liquidity index IL (-)		NA	0.36	0.22	0.30	0.51	0.40	0.49	0.47
Design value of γd (kN·m−3)		20.890	20.890	21.209	21.027	20.549	20.799	20.594	20.640
Design value of φd (°)		11.01	11.01	13.03	11.88	8.856	10.44	9.14	9.43
Design value of cd (kPa)		10.37	10.37	15.04	12.16	6.96	9.32	7.34	7.74
Thickness h (m)		0.20	0.15	0.10	0.10	0.15	0.15	0.40	0.35
Factor of safety Fs (-)		4.73	6.41	13.65	10.99	4.19	5.74	NA	NA
IL = 0.75 (flowing water)	γd (kN·m−3)	20.033	20.003	20.003	20.003	20.033	20.003	20.003	20.003
	φd (°)	5.40	5.40	5.40	5.40	5.40	5.40	5.40	5.40
	cd (kPa)	3.67	3.67	3.67	3.67	3.67	3.67	3.67	3.67
Factor of safety Fs (-)		1.25	1.67	2.45	2.45	1.67	1.67	NA	NA
IL = 1.00 (flowing water)	γd (kN·m−3)	19.434	19.434	19.434	19.434	19.434	19.434	19.434	19.434
	φd (°)	1.80	1.80	1.80	1.80	1.80	1.80	1.80	1.80
	cd (kPa)	1.89	1.89	1.89	1.89	1.89	1.89	1.89	1.89
Factor of safety Fs (-)		0.66	0.87	1.28	1.28	0.87	0.87	NA	NA

. Sample 1 contains more gravel particles than sample 2 due to clayey shales sliding onto the slope (see also Figure 1b). Values of the factor of safety in Table 5 show that slope 1 is not stable in the case of flowing water, even when I_L = 0.75.

As mentioned, a roughly 0.15 m layer of topsoil from the left part and a 0.10 m layer from the right part of slope 1 were removed (in total about 7.5 m³ of soil), placed on the road surface, mixed with a backhoe loader, and then compacted back onto the slope. Therefore, the grain-size distribution curves of the soils represented by samples 5 and 6 (soils on the slope, green diagram) and sample 8 (just behind the right part of the wall, red diagram) are similar. In contrast, the diagram for sample 7 (just behind the left part of the wall, thick red diagram) is different, showing more gravelly and sandy particles because clayey shales slid onto the slope after the rope installation.

Stability analysis shows that the slope is not stable in the case of flowing water and the proposed I_L = 1.00. The left part of the future stabilized slope would have slid even at I_L = 0.75. Thanks to the ropes installed in the slope and in the wall at the base of the slope, the stabilized slope has remained stable for the entire period since their installation in October 2008. Meanwhile, landslides occurred on the left side of the stabilized slope, as well as in other areas.

Figure 12 presents the ropes after 65 months from installation. The wool fibers in the wool rope underwent complete microbiological biodegradation. The fibers in the RNSF rope were of different types and showed varying degrees of degradation. The fibers in the PP rope did not appear to be degraded.

Figure 13 presents SEM images of wool fibers (Figure 13a,b); waste textile fibers (Figure 13c,d), and PP fibers (Figure 13e,f). The wool fibers underwent microbiological biodegradation through keratin decomposition—a process that involved the gradual breaking of disulfide bridges and peptide bonds, leading to defibrillation, erosion, and loss of fiber integrity, which appeared as microcracks and delamination in the SEM images (Figure 13b). The waste textile, which contained both natural and synthetic fibers, degradation primarily affected the fraction composed of natural fibers (sheep wool, cotton), while the synthetic fibers retained a smooth, undamaged surface, resulting in selective weakening of the composite structure (Figure 13d). The polypropylene fibers remained resistant to biodegradation—only minor mechanical damage was observed, and the absence of signs of biological degradation confirmed their high durability (Figure 13f).

3.3. Soil Load on the Rope

After 65 months had elapsed subsequent to installation, wool, RNSF, and PP rope samples were taken in order to determine their tensile strengths; the results are presented in

Table 7. Properties of the waste wool, waste textile, and PP nonwoven materials.

Nonwoven Materials		Months	Tensile Strength (kN.m−1)	Elongation at Break (%)	Design Tensile Strength of Ropes TD (ULS) (kN)
Wool waste (slope—left)		0	5	42.4	6.818
		65	Degraded, not tested	Degraded, not tested	NA
Recycled textile wastes (slope—right)		0	3.80	35.2	6.218
		65	2.46 (35.26% reduction)	20.95 (40.14% reduction)	4.025 (35.26% reduction)
Polypropylene	wall—left, top	0	3.03	35.67	4.131
		65	2.38 (21.45% reduction)	19.82 (44.43% reduction)	3.245 (21.45% reduction)
	wall—left, bottom	0	3.03	35.67	4.131
		65	2.73 (9.90% reduction)	18.69 (47.60% reduction)	3.723 (9.90% reduction)
	wall—right, top	0	3.03	35.67	4.131
		65	2.84 (6.27% reduction)	15.08 (57.72% reduction)	3.873 (6.27% reduction)
	wall—right, bottom	0	3.03	35.67	4.131
		65	2.38 (21.45% reduction)	18.39 (48.44% reduction)	3.245 (21.45% reduction)

. Based on material tensile strength, rope design tensile strength was calculated and compared with the tension force induced in the ropes on the slope and the rope in the wall (see

Table 8. Design tension force in the ropes on the slope and in the wall, in comparison with the rope design tensile strength.

Parameters (See Table 6 for Values of IL and Soil Properties)		Design Tension Force in Rope and Rope Design Tensile Strength
		Wool (Diameter d = 8 cm)	RNSF Rope (Diameter d = 8 cm)	PP Rope (d = 4 cm)
				Wall—Left, Bottom	Wall—Right, Bottom
State on 6 March 2024	Tj (kN)	No force	No force	1.504	1.188
	TD (kN)	Degraded, not tested	4.025	3.723	3.245
State for proposed IL = 0.75	Tj (kN)	No force	No force	1.481	1.294
	TD (kN)	Degraded, not tested	4.025	3.723	3.245
State for proposed IL = 1.00	Tj (kN)	0.113	0.112	1.455 (no rope: 1.804)	1.410 (no rope: 1.786)
	TD (kN)	Degraded, not tested	4.025	3.723	3.245

Note: Diameter of the rope on the slope d = 8 cm; cover soil thickness on the slope 7 cm; diameter of the rope in the wall d = 4 cm; height of the left wall part 0.4 m (0.3 m of rope; 0.1 m of cover soil); height of the right wall part 0.35 m (0.35 m of rope; no cover soil); Tj: design tensile force in the rope; TD: design tension strength of the rope; strain of the wool rope on the left slope part 9.80%; strain of the RNSF rope on the right slope part 10.40%; strain of the PP rope in the left wall part 2.60%; strain of the PP rope in the right wall part 2.20%; height of water behind the left wall part 0.30 m; height of water behind the right wall part 0.35 m.

).

Even though no mechanical damage is visible on the wool rope, which is characterized by a thickness of about 6 cm, due to the effects of water and temperature, the fibers have become felted, causing the sample to disintegrate in the hand, so the tensile strength of the wool on the slope was practically null after 65 months (degraded, not tested).

The tensile strength of the RNSF nonwoven on the slope is 2.46 kN·m⁻¹, reduced by 1.34 kN·m⁻¹ (35.26%). The actual value of 2.46 kN·m⁻¹ is much greater than the value of 0.112 kN·m⁻¹, which is expected during water flow on the slope and at I_L = 1.

The tensile strength of the PP nonwoven taken from various positions in the wall varies from 2.38 kN·m⁻¹ (wall—left, top; and wall—right, bottom) to 2.84 kN·m⁻¹ (wall—right, top). The tensile strength of the PP was reduced differently, by 0.19 kN·m⁻¹ (6.27%; wall—right, top) to 0.65 kN·m⁻¹ (21.45%; wall—left, top; and wall—right, bottom). There is no clear pattern in the reductions in the tensile strengths of the PP textiles taken from different locations. We assume that this is due to the existence of many factors influencing the degree of tensile strength reduction, such as UV radiation, temperature fluctuations, freeze–thaw, mechanical abrasion from soil and ropes, minor chemical exposure, biological factors, different loads, etc. This is a complex issue, and it requires further research. We propose that this moderate reduction after 65 months is partly attributed to the outer layer of the retaining wall, made of sheep wool, which not only has an aesthetic function but also provides partial protection against UV radiation, temperature fluctuations, and other environmental stressors. The inherent chemical stability of polypropylene further contributed to the relatively low rate of degradation over the observed period.

As we can see, in all cases, the design tensile strength of the PP rope is larger than the design tension force (see Table 8). It is worth noting that for the soil state on 06 March 2024 with the corresponding liquidity index I_L (see Table 6) and for the proposed state of liquidity index I_L = 0.75, the slope is stable even without ropes on the slope. In these cases, tension forces in the PP rope exist due to water and soil pressure behind the wall. In the worst-case proposition, I_L = 1.0 (flowing water on the slope, soil in a liquid state), the design tensile strength of the PP rope forming the wall is also sufficient. If the rope on the slope does not help, the design tensile strength of the PP rope is still sufficient (wall—left, bottom rope: 3.723 kN·m⁻¹ in comparison with 1.804 kN·m⁻¹; wall—right, bottom rope: 3.245 kN·m⁻¹ in comparison with 1.786 kN·m⁻¹), so the wall is stable. The condition of the RNSF and PP ropes on 4 March 2024 is good and no damage is seen (see Figure 3b–d). It is proposed that due to the existence of wool and RNSF ropes on the slope and grass roots, the force of flowing water is restricted. Furthermore, to be damaged, the strain of the rope should be larger than the measured values (the strain of RNSF rope is 10.40%); but thanks to the wall, soil movement on the slope is limited and the strains remain relatively small.

The results of the material strength test as well as the monitoring show that the ropes, both on the slope and in the retaining wall, have been fulfilling their function for the entire time since installation. The tensile strength of the RNSF nonwoven on the slope at present is 2.46 kN·m⁻¹ (after 65 months). This value is comparable to the value of 3.0 kN·m⁻¹ (after 47 months) reported for the RNSF in Nieboczowy [16]. The design tensile strength of the rope will then be 4.025 kN, which is much greater than the maximum tensile force induced in the rope in the wall (1.455 kN). This fact justifies the assumption that RNSF can potentially be used as a material for the retaining wall. On the other hand, the force induced in the rope in this study is only calculated. It is therefore necessary in further research to install sensors to determine the actual force induced in the rope.

3.4. Qualitative Evaluation of Slope Erosion

The monthly precipitation in Oravská Lesná according to [37] is presented in

Table 9. Monthly precipitation (mm) in Oravská Lesná according to [37].

Months, Years	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total
2009	44	109	212	12	107	115	127	106	42	161	68	69	1172
2010	52	42	86	54	295	142	220	246	148	27	98	111	1521
2011	55	46	16	80	62	148	206	55	40	60	2	106	876
2012	231	121	60	51	50	154	105	41	82	127	61	48	1131
2013	140	82	57	28	139	100	31	159	133	43	116	60	1088
2014	40	38	111	86	107	105	143	132	89	61	33	106	1051
2015	131	59	86	80	109	47	99	55	94	59	225	40	1084
2016	86	174	27	59	117	78	226	101	50	151	90	136	1295
2017	60	87	76	182	97	116	187	96	195	203	113	82	1494
2018	62	32	37	26	116	148	133	117	100	97	12	173	1053
2019	200	35	98	40	190	28	132	166	108	57	109	105	1268
2020	41	195	58	12	147	152	81	65	109	178	24	59	1121
2021	108	60	50	88	153	38	117	230	53	19	59	81	1056
2022	142	128	30	98	56	95	95	114	208	68	45	83	1162
2023	127	175	75	44	82	55	132	162	95	132	163	151	1393
2024	148	118	48	79	64	126	75	76	111	46	54	33	978
2025	77	22	42	51	111	43	168	42	157

and in Figure 14. A consideration of Figure 14 shows that the annual precipitation is fairly uniform, and the yearly total is around 1000 mm. According to [43], the elevation above sea level H of the slope center is about 890 m. Based on these values, the rainfall erosivity factor R_r was calculated using Formulas (1)–(5). The runoff erosivity factor R_s was calculated as the average value of one-tenth of the amount of December through March precipitation for the period from 2009 to 2025, and has a value of 34.462 (MJ·cm·ha⁻¹·h⁻¹·y⁻¹). The rainfall and runoff erosivity factor R was calculated using Formula (11), and the results are presented in

Table 10. Values of rainfall and runoff erosivity factor R and soil erodibility factor K_w.

Taken On	17 June 2018 (Before Rope Installation)				4 March 2024 (After Rope Installation)
Sample	1	2	3	4	5	6	7	8
Soil classification [28]	Żg	Pog	Pog	Pog	Żg	Pog	Żg	Pog
Location	Slope 1 (left)	Slope 1 (right)	Slope 2 (upper)	Slope 2 (lower)	Slope 1 (left) (wool rope)	Slope 1 (right) (RNFS rope)	Behind wall (PP rope, left)	Behind wall (PP rope, right)
R ((MJ·cm)/(ha·h·year)), form. (1) and (10), max.	161.914	161.914	161.914	161.914	161.914	161.914	161.914	161.914
R ((MJ·cm)/(ha·h·year)), form. (3) and (10), min.	121.549	121.549	121.549	121.549	121.549	121.549	121.549	121.549
R ((MJ·cm)/(ha·h·year)), average	142.059	142.059	142.059	142.059	142.059	142.059	142.059	142.059
Grain-size distribution curve number	1	2	3	4	5	6	7	8
Kf (for fraction to 2 mm), (t·ha·h)/(ha·MJ·cm), form. 11 (10)	0.24482	0.29178	0.29325	0.23885	0.30656	0.29412	NA	NA
Kw (for whole soil), (t·ha·h)/(ha·MJ·cm) [36]	0.04000	0.14253	0.15412	0.09562	0.08079	0.09777	NA	NA

and

Table A2. Values of rainfall and runoff erosivity factor R and soil erodibility factor K_w.

Taken On	17 June 2018 (Before Rope Installation)				4 March 2024 (After Rope Installation)
Sample	1	2	3	4	5	6	7	8
Soil classification [31]	Żg	Pog	Pog	Pog	Żg	Pog	Żg	Pog
Location	Slope 1 (left)	Slope 1 (right)	Slope 2 (upper)	Slope 2 (lower)	Slope 1 (left) (wool rope)	Slope 1 (right) (RNFS rope)	Behind wall (PP rope, left)	Behind wall (PP rope, right)
Rr ((MJ·cm)/(ha·h·year)), form. (1), max.	127.452	127.452	127.452	127.452	127.452	127.452	127.452	127.452
R ((MJ·cm)/(ha·h·year)), form. (1) and (10), max.	161.914	161.914	161.914	161.914	161.914	161.914	161.914	161.914
Rr ((MJ·cm)/(ha·h·year)), form. (2)	116.132	116.132	116.132	116.132	116.132	116.132	116.132	116.132
R ((MJ·cm)/(ha·h·year)), form. (2) and (10)	150.595	150.595	150.595	150.595	150.595	150.595	150.595	150.595
Rr ((MJ·cm)/(ha·h·year)), form. (3), min.	87.086	87.086	87.086	87.086	87.086	87.086	87.086	87.086
R ((MJ·cm)/(ha·h·year)), form. (3) and (10), min.	121.549	121.549	121.549	121.549	121.549	121.549	121.549	121.549
Rr ((MJ·cm)/(ha·h·year)), form. (4)	94.957	94.957	94.957	94.957	94.957	94.957	94.957	94.957
R ((MJ·cm)/(ha·h·year)), form. (4) and (10)	129.419	129.419	129.419	129.419	129.419	129.419	129.419	129.419
Rr ((MJ·cm)/(ha·h·year)), form. (5)	112.354	112.354	112.354	112.354	112.354	112.354	112.354	112.354
R ((MJ·cm)/(ha·h·year)), form. (5) and (10)	146.817	146.817	146.817	146.817	146.817	146.817	146.817	146.817
R ((MJ·cm)/(ha·h·year)), average	142.059	142.059	142.059	142.059	142.059	142.059	142.059	142.059
Grain-size distribution curve number	1	2	3	4	5	6	7	8
Clay fraction (c), <0.002 mm (%) [38]	18.83	24.55	30.52	27.24	11.94	11.56	NA	NA
Silt fraction, total, (si) ≥0.002 and <0.05 (%) [38] (%) [28]	39.06	50.92	54.90	42.84	40.09	37.41	NA	NA
Very fine sand fraction (vfs), ≥0.05 and <0.1 (%) [38]	2.95	2.11	2.95	2.98	7.43	8.16	NA	NA
Rock fragments (%) [38]	74.28	28.34	25.63	37.04	53.75	46.76	NA	NA
M (-) [38]	3410.71	4001.87	4020.16	3334.68	4185.27	4030.93	NA	NA
Kf (for fraction to 2 mm), (t·ha·h)/(ha·MJ·cm), form. 10 (10)	0.24482	0.29178	0.29325	0.23885	0.30656	0.29412	NA	NA
Kw (for whole soil), (t·ha·h)/(ha·MJ·cm) [38]	0.04000	0.14253	0.15412	0.09562	0.08079	0.09777	NA	NA

, with an indication of the formulas for which the minimal and maximal values of R were obtained. The average value of all rainfall and runoff erosivity factors R is also calculated and presented in Table A2. Values of the soil erodibility factor K_f (for the fraction up to 2 mm), and the soil erodibility factor K_w (for the whole soil) are also presented in Table 10.

Slope parameters are presented in

Table A3. Values of actual erosion rate E_A and potential erosion rate E_P for minimal, average, and maximal rainfall and runoff erosivity factor R, and corresponding erosion classes.

Location	Slope 1 (Left)		Slope 1 (Right)		Slope 2 (Upper)	Slope 2 (Lower)
	With Ropes	If Without Ropes	With Ropes	If Without Ropes	Without Ropes	Without Ropes
λ (m)	7.40	7.40	7.40	7.40	7.40	7.40
m (-)	0.5	0.5	0.5	0.5	0.5	0.5
q (°)	40.0	40.0	40.0	40.0	45	45
L (-)	0.578	0.578	0.578	0.578	0.578	0.578
S (-)	30.253	30.253	30.253	30.253	36.226	36.226
LS (-)	17.494	17.494	17.494	17.494	20.948	20.948
Kw (t·ha·h)/(ha·MJ·cm) [18,36]	0.08079	0.04000	0.09777	0.14253	0.15412	0.09562
C (-)	0.01	0.22	0.01	0.22	0.22	0.22
P (-)	1.00	1.00	1.00	1.00	1.00	1.00
Actual and potential erosion rate and corresponding classes for minimalrainfall and runoff erosivity factor R
EA (t·ha−1·year−1)	1.718	18.713	2.079	66.681	86.334	53.566
Actual erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
EP (t·ha−1·year−1)	1.718	85.057	2.079	303.094	392.427	243.482
Potential erosion class	(1) No erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
Actual and potential erosion rate and corresponding classes for average rainfall and runoff erosivity factor R
EA (t·ha−1·year−1)	2.008	21.870	2.430	77.932	100.902	62.604
Actual erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
EP (t·ha−1·year−1)	2.008	99.409	2.430	354.237	448.644	284.566
Potential erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
Actual and potential erosion rate and corresponding classes for maximal rainfall and runoff erosivity factor R
EA (t·ha−1·year−1)	2.289	24.927	2.770	88.825	115.005	71.355
Actual erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
EP (t·ha−1·year−1)	2.289	113.304	2.770	403.749	522.749	324.340
Potential erosion class	(2) Weak erosion	(6) Very strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion

. Values of the actual erosion rate E_A and the potential erosion rate E_P were calculated using Formulas (8) and (9) and are presented in

Table 11. Values of actual erosion rate E_A and potential erosion rate E_P for minimal, average, and maximal rainfall and runoff erosivity factor R and corresponding erosion classes.

Location	Slope 1 (Left)		Slope 1 (Right)		Slope 2 (Upper)	Slope 2 (Lower)
	With Ropes	If Without Ropes	With Ropes	If without Ropes	Without Ropes	Without Ropes
Actual and potential erosion rate and corresponding classes for minimalrainfall and runoff erosivity factor R
EA (t·ha−1·year−1)	1.718	18.713	2.079	66.681	86.334	53.566
Actual erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
EP (t·ha−1·year−1)	1.718	85.057	2.079	303.094	392.427	243.482
Potential erosion class	(1) No erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
Actual and potential erosion rate and corresponding classes for average rainfall and runoff erosivity factor R
EA (t·ha−1·year−1)	2.008	21.870	2.430	77.932	100.902	62.604
Actual erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
EP (t·ha−1·year−1)	2.008	99.409	2.430	354.237	448.644	284.566
Potential erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
Actual and potential erosion rate and corresponding classes for maximal rainfall and runoff erosivity factor R
EA (t·ha−1·year−1)	2.289	24.927	2.770	88.825	115.005	71.355
Actual erosion class	(2) Weak erosion	(5) Strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion
EP (t·ha−1·year−1)	2.289	113.304	2.770	403.749	522.749	324.340
Potential erosion class	(2) Weak erosion	(6) Very strong erosion	(2) Weak erosion	(6) Very strong erosion	(6) Very strong erosion	(6) Very strong erosion

. Based on these values and the classification criteria from Table 4 and Table 5, the corresponding erosion classes were determined. As we can see, due to the installed ropes, the slope is covered with vegetation, and its erosion rate is classified as “No erosion” (potential erosion class, slope–left) when the minimum rainfall and runoff erosivity factor R is applied in the soil loss computation, or as “Weak erosion” in all other cases, including those using the maximum R-factor value.

Hypothetical soil loss estimations were also performed for the scenario in which no ropes were installed on the slope. The results indicate that under such conditions, the slope would fall into the “Strong erosion” to “Very strong erosion” classes. The reference slope without ropes is classified as “Very strong erosion” even when the minimum rainfall and runoff erosivity factor R is used in the soil loss computation.

It is worth noting that different formulas for calculating the average annual rainfall erosivity factor R_r (from (1) to (5)) yield considerably different values. Formula (1) gives the maximum value of R_r = 127.452 (MJ·cm·ha⁻¹·h⁻¹·y⁻¹), while Formula (3) gives the minimum value of R_r = 87.086 (MJ·cm·ha⁻¹·h⁻¹·y⁻¹) (see Table A2). This difference of 40.366 (MJ·cm·ha⁻¹·h⁻¹·y⁻¹), corresponding to 31.67%, results in variations in the calculated average rainfall and runoff erosivity factor R (see Formula (10)) and, consequently, in soil loss across all locations (by 24.93% higher). It also changes the erosion class: the maximum R_r according to Formula (1) results in the potential erosion class “Weak erosion” (Slope 1—left, with rope), whereas the minimum R_r obtained from Formula (3) results in the potential erosion class “No erosion” (Slope 1—left, with rope), see Table 10. The soil loss values shown in Table 10 indicate that even when the maximum R_r (and thus R) is used, the potential erosion class remains “Weak erosion,” which supports the conclusion about the effectiveness of the rope as an anti-erosion measure.

The studied slope was also qualitatively evaluated in terms of erosion [43]. The results show that the examined slope with the rope is without erosion, which corresponds to the minimum R_r obtained from Formula (3). Therefore, it is recommended that in further research erosion be evaluated not only quantitatively but also qualitatively. In this way, the erosion class can be verified.

4. Discussion

The monitoring results demonstrate that the polypropylene (PP) ropes and the RNSF nonwoven on the slope and in the retaining wall have successfully fulfilled their functions since installation. This case represents a novel application of PP nonwoven ropes threaded through iron rods to form a layered retaining wall, a technique which has not been previously reported.

Unlike previous cases [13,14,15,16,17], where wool and textile waste ropes were placed meanderingly (parallel) to the slope edge, in this case the ropes were laid in a rhomboid pattern, which better drained the water, which in flysch areas, not only flows down the slope but often also emerges from beneath it. Monitoring results showed that the slope has been well drained and stable since its installation in October 2018, providing evidence that the ropes can be applied across a range of geological and hydrogeological conditions. This provides a further case confirming the conclusion presented in a thorough and comprehensive review on polymeric products in erosion control applications [44], where the authors state that geosynthetic elements allow erosion control measures to be placed even in difficult hydraulic conditions.

The tensile strength of the RNSF rope is higher than the residual strength of polypropylene nonwoven after 65 months and much higher than the load in the rope forming the wall. This fact allows us to assume that ropes made of textile waste could also be used in a retaining wall in a way similar to the use of polypropylene nonwoven. However, this is a complex issue, since the strength of textile waste strongly depends on its composition as well as on environmental, biological, chemical, and mechanical factors; therefore, further research will be necessary.

Determinations of the rainfall erosivity factor $R_r$ according to various authors provide different values. The maximum value was obtained according to [20] and the minimum according to [23]; see Table 10. The difference between them, 40.366 ((MJ·cm)/(ha·h·year))—corresponding to 31.67%—results in higher soil loss across all locations (by 24.93%). However, the maximum soil loss value calculated according to [20] still classifies the slope with ropes as belonging to the “Weak erosion” class (both actual erosion class and potential erosion class) compared with the class “Strong erosion” (actual erosion class) or “Very strong erosion” (potential erosion class) if the ropes had not been used. This confirms the effectiveness of the applied method.

Although the use of unit weight and shear strength parameters in this study complies with standards and design practice, further research or larger-scale projects should include tests to verify these parameters. It would be appropriate to measure the forces in the ropes and compare them with calculated values.

Similar demonstrations of best practices involving geotextile reinforcement were investigated in [45,46]. The authors of [45] present a physical model for the experimental investigation of a foam concrete (FC) subbase layer of an industrial floor at full scale. The results show that using Filtek 200 geotextile with a weight of 200 g·m⁻² at the base, together with basalt reinforcing mesh type ORLITECH MESH, increased the strain modulus values from 29 MPa to 80 MPa (for FC 500 with a thickness of 12 cm) and from 16 MPa to 102 MPa (for FC 500 with a thickness of 22 cm). The authors of [46] present laboratory tests of the flexural strength of FC with various unit weights using the same geotextile and reinforcing mesh. The results show that the addition of geotextile contributed to a 30–60% increase in the first-crack flexural strength compared to plain FC. The additional mesh increased the basic flexural strength approximately twofold. As an alternative, there is a plan to incorporate nonwoven fabrics and ropes made from textile waste (approximately 2 cm in diameter) into different layers of the panel. This reinforcement is expected to reduce cracking and brittleness of FC while improving its dynamic and mechanical performance.

5. Conclusions

This study confirms that PP ropes and RNSF can function effectively as layered retaining structures, offering a practical and sustainable solution for civil and environmental engineering. The approach demonstrates both novelty and potential for broader application, providing cost-effective and environmentally friendly alternatives, including the possible use of waste textiles.

The findings underscore the practical significance of this method along stream banks, bicycle paths, and steep horticultural slopes.

Further research is recommended to measure the actual forces in the ropes, validate calculated values, and explore additional applications and long-term performance under varied conditions. These conclusions highlight the broader relevance and potential impact of using PP ropes and RNSF as layered retaining structures.