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Reclamation of abandoned open mines with innovative meandrically arranged geotextiles
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Technical note
Reclamation of abandoned open mines with innovative meandrically arranged geotextiles Jan Brodaa,∗, Petra Franitzab, Ulrich Herrmannb, Reinhard Helbigb, Anna Großeb, Joanna Grzybowska-Pietrasa, Monika Roma a b
Institute of Textile Engineering and Polymer Materials, University of Bielsko-Biala, Bielsko-Biala, Poland Saxon Textile Research Institute, Chemnitz, Germany
A R T I C LE I N FO
A B S T R A C T
Keywords: Geosynthetics Open mine reclamation Kemafil technology Vegetation restoration
For over fifty years, geosynthetics have been used for land reclamation of degraded areas. Several years ago for this purpose innovative geotextiles formed from meandrically arranged thick ropes were invented. The geotextiles were used for reclamation of abandoned lignite open-mine in Germany and disused gravel pit in Poland. The geotextiles were installed in abandoned mines. In next years positive influence of geotextiles on slopes behaviour and vegetation was observed. It was stated that the geotextiles provide stabilization of steep unstable slopes and significantly accelerate vegetation development. The innovative geotextiles perform functions unobtainable for other traditional products. The products are useful in an effective reclamation of open mines and constitute a valuable extension of the geosynthetic assortment applicable in land reclamation.
1. Introduction For many years opencast mining is a commonly used for extraction of brown coal, ore, sand, gravel and other mineral resources. Extraction of mineral deposits shallowly located under the land surface is efficient and cost-effective. Nevertheless, the process generates considerably environmental problems and has a severe negative impact on a surrounding landscape and other elements of the local ecosystem. Intensive mining leads to land degradation, which after closing the mine, requires satisfactory restoration. Usually, restoring of degraded land to its original state is difficult and economically unreasonable. In this situation degraded post-mining areas are subject to reclamation, which ends up in a new state where the structure or function of the land is different from the original. The effective reclamation requires a series of measures to protect unstable slopes and restore the vegetation. Vegetation has an important role in protecting the soil surface from erosion. Plants grew on the slope decrease soil bulk density, moderate soil pH, increase soil organic matter and accumulate mineral nutrients in the layer closed to the soil surface. Additionally, on a macro scale vegetation restores the beauty and productivity of the land (Schor and Gray, 2007; Hutnik and McKee, 1990). For the above reasons, the re-establishing of vegetation is a major challenge and a key indicator of reclamation success (Sheoran et al., 2010).
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Due to physical and biological conditions unfavourable for plant growth, re-establishing of vegetation may be difficult. The growth of the plant cover can be constrained by improper soil structure and its inadequate particles size distribution, water shortage, gross lack of certain nutrients and soil toxicity (Peris et al., 2017). Re-establishing of vegetation may be extremely hard in a dry climate and on steep slopes endangered by severe erosion (Moreno-de las Heras et al., 2008; Moreno-de las Heras et al., 2009). In temperate climate re-establishment of vegetation may occur as a result of a spontaneous process. Species colonized through spontaneous succession are well adapted to local site conditions, exhibit higher diversity and possess greater natural value. Nevertheless, reaching the target state of spontaneously grown vegetation is a long-term process and often takes several years (Borgegård, 1990; Rehounkova and Prach, 2008; Prach et al., 2013; Prach et al., 2014). To accelerate vegetation development in degraded land different techniques can be applied (Bradshaw and Chadwick, 1980; Bradshaw, 1997, 2000; Kiehl et al., 2010; Baasch et al. 2012; Kuter, 2013; Mudrák et al., 2016). One method, commonly used for several years consists on an application of geosynthetics (Theisen, 1992; Kumar and Das, 2018; Ngo et al., 2019; Nsiah and Schaaf, 2019). A wide assortment of geosynthetics suitable for mines reclamation includes erosion control products, such as mats and blankets, which are installed in a very close contact with the ground surface (Ogdobe et al.
Corresponding author. E-mail address: [email protected] (J. Broda).
https://doi.org/10.1016/j.geotexmem.2019.11.003 Received 28 August 2018; Received in revised form 19 November 2019; Accepted 19 November 2019 0266-1144/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Jan Broda, et al., Geotextiles and Geomembranes, https://doi.org/10.1016/j.geotexmem.2019.11.003
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1998; Ahn et al. 2002; Shao et al., 2014; Prambauer et al., 2019). The second group of products includes three-dimensional turf-reinforcement mats, which are designed to be seeded and then filled with the soil (Carroll et al., 1992; Weggel and Rustom, 1992; Wu and Austin, 1992; Pritchard et al., 2000; Rickson, 2006; Shukla, 2016). In addition to such products for the reclamation of mines flexible fibre rolls may be adapted. Rolls are tube-shaped devices filled with straw, rice husks, flax, coconut fibres or other organic composting material wrapped in a netting made from natural or synthetic polymer materials (Etra, 2011). Certain products are formed from blankets rolled into large diameter logs. Depending on their destination, the rolls with various length and diameters can be produced. The rolls are installed on the slopes in dug shallow trenches at a depth equal to half of the diameter of the log and hold in place by wooden stakes. Flexible rolls can be bent along the contours of the land and can be coiled into a circle (Baxter, 2008). The rolls installed transversally on the slopes form a system of micro-dams, which breaks up the slopes and reduces the velocity of water flowing on the surface (García et al., 2015). Several years ago for the production of fibre rolls the Kemafil technology was applied (Berthold and Arnold, 1975; Helbig et al., 2006a). In initial tests, ropes with the diameter of 50 mm were obtained. The ropes made from textile waste were applied for the protection of banks of an expansion tank and sandy roadside slopes. In the protected places, straight ropes were diagonally spread on the slopes to form squares of 60–70 cm and fastened to the ground with metal anchors. Following the installation, the grid formed by the ropes was covered with soil and sown with grass seeds. It was revealed that the grid made from the ropes effectively protects the slopes and positively affects plant vegetation. In the next studies thicker ropes, with the diameter of up to 130 mm, were manufactured. The ropes were arranged in a meanderlike pattern to form bigger segments. To stabilise the segments, the subsequent turns of ropes were connected with additional linking chains (Helbig et al., 2006b). The meandrical arrangement ensured the high mechanical strength of the segments both, longwise and crosswise. The segments formed from meandrically arranged ropes were successfully used for the protection of road embankments and drainage ditches (Broda et al. 2016, 2017, 2018). In further studies, segments were used for reclamation of abandoned open-mines. The ropes were installed on a steep and unstable slope in disused lignite pit mine in eastern Germany as well as on steep slope in the abandoned gravel pit in southern Poland. In the paper, the installation of ropes is presented. The stability of slopes and their greening during several years of exploitation is analysed. The effectiveness of ropes in the reclamation of disused mines is evaluated and their role in slopes stabilization and vegetation development is explained.
Fig. 1. Kemafil technology: a/the guiding tube and the loopers; b/the rope.
levelled slope, anchored to the top of the slope and fastened to its surface with steel “U-shaped” pins. Later the segments were covered with a layer of topsoil. After geotextiles installation stability of slopes and their greening were regularly monitored. During three vegetation seasons, potential soil movements, as well as erosion rills and gullies, were observed. An impact of geotextiles on land sliding and surface erosion was qualitatively assessed. Simultaneously, development of vegetation on the protected slopes was analysed. During observations intensity of green cover in particular vegetation seasons was analysed. Moreover, the plant species appeared on the slopes were identified and their range of cover was estimated. 3. Opencast lignite mine Zechau 3.1. Site characteristics The inoperative opencast lignite mine Zechau is located at 51°00′ N and 12°19’ E in the north-west part of the Thuringian district – Altenburger Land, between the cities Meuselwitz and Altenburg (Germany). The terrain is situated at an altitude of 230 m above sea level in temperate climate zone. The average annual temperature for this place equals 8.6 °C, while the mean annual precipitation is 551 mm. For more than 100 years, an extensive opencast lignite mining was carried out in the region. Mining has profoundly transformed the landscape and led to a significant change of various environmental components. After the closure of the mines, in order to make the large areas suitable for agriculture, forestry and nature conservational activities, the former lignite mining facilities were reclaimed. The main task was to integrate the reclaimed lands into the surrounding landscapes and to restore the populations of flora and fauna. Zechau opencast brown coal mine was opened in 1931 and closed after 28 years of operation in 1959. The excavation site with the surface area of approximately 4.5 km2 was partially filled with water. In the following years, the area became part of the European nature protection zone Natura 2000. The reserve Restloch Zechau with the surface area of 213 ha gained the status of the protected area in 2000 and became the habitat for rare species of animals and plants (Fig. 2) (Krummsdorf et al., 1998). After the closure of the mine, a deep hole with steep slopes remained on the site. The denuded slopes formed from sandy soil mixed with brown coal remnants were prone to local sliding (Fig. 3). Additionally, the brown coal deposits exposed to high solar radiation, especially on the southwest side, had a tendency to self-ignite. As a result, the slopes were often on fire, emitting irritating odours and smoke. Frequently smouldering slopes became unbearable for the local residents.
2. Materials and methods For reclamation of abandoned mines geotextiles formed from thick ropes were applied. The ropes were manufactured from textile materials, nonwovens made from biodegradable natural fibres and nonbiodegradable synthetic fibres. A part of the ropes was produced from recycled fibres obtained by shredding of post-consumer textile wastes. For the production of ropes, the Kemafil technology was applied. The technology involves use of a small circular knitting machine, which is equipped with four hooked loopers arranged around the guiding tube (Fig. 1a). The threads guided by the loopers from a tubular sheath around the thick rope core (Fig. 1b) (Arnold et al., 1993, 1995). The ropes were arranged into a meander-like pattern to form twodimensional flat segments. Inside segments the ropes were connected with additional linking chains. Dimensions of segments, a distance between the successive turns of the ropes as well as the number and the distribution of transverse links were adapted to terrain conditions. Segments were rolled up and transported to the installation site. Then they were rolled out and unfolded on the surface of the profiled and 2
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Fig. 2. Inoperative excavation of the lignite mine Zechau; a/the hole filled with water.
3.2. Materials For reclamation of the lignite mine, coarse Kemafil ropes with the diameter of 120 mm were produced. As rope filling material voluminous stitch-bonded polyester nonwoven with good water storage properties was applied. The nonwoven was manufactured by Maliwatt technology and had thickness 3 mm and surface density 200 g/m2. The core of the ropes was wrapped with a covering spun-laced polyester nonwoven with thickness 1 mm and surface density 80 g/m2. The ropes were sheathed with a mesh made from polypropylene multifilament with the thickness of 220 tex. In the central part of the ropes a perforated irrigation tube with the outer diameter φ = 12 mm was inserted (Fig. 4). The ropes were used to form 1.8 m wide and 20 m long meandrically arranged segments. The links between the subsequent turns of the ropes were made with a hybrid thread that was composed of polyethylene tapes (18 cm width and 0.2 mm thick) and high-density polypropylene threads (18 filaments, each 220 tex). To avoid kinking of the irrigation tubes placed inside the ropes the optimal interval of 0.6 m between the rope-meanders was established. To improve the settlement of the topsoil between the meanders, additional thinner ropes without irrigation tube were mounted.
Fig. 4. The structure of the Kemafil rope with the integrated irrigation tube.
After preparatory works and slope levelling the rolled segments of the geotextiles were placed on the crown of the slope. Subsequently, the segments were fixed on the top shelf and then rolled down the slope. The ropes were fastened to the slope with the U-shaped soil nails fabricated from steel ribbed bars with the length of 60 cm and the diameter φ = 10 mm. Finally, the geotextiles were covered with a 15 cm layer of weakly binding humus soil (Fig. 5). According to DIN 18915:2002–08 the soil, so-called German Kulturboden, belongs to floor group 4, possesses pH 5,0–5,5 and consists of 15–20% slurriable particles, 10–15% coarse soil and 3–4% humus. Once covered, the slope was seeded with a mixture of grass seeds, e.g. festuca ovina duriuscula, festuca rubra commutata, festuca rubra rubra and festuca rubra trichophylla, usually used for reclamation, greening and stabilising light soils to guard against erosion. During installation, the geotextiles were combined with irrigation and monitoring systems and coupled with the local public water supply source. The system was divided into 12 watering circuits, which were steered by impulse controlled solenoid coils. Irrigation was activated three times a day, for 30 min each time. Additionally, the integrated temperature and humidity sensors were connected to the irrigation control system. If the humidity dropped below 50% or the soil
3.3. Geotextiles installation The denuded slope prone to land sliding located on the southwest side of the pit with the total length of 200 m and area of 4000 m2 was protected. The average height of the slope was 10 m and its inclination length equalled 20.5–21.5 m. Before installation of geotextiles, the slope was profiled and levelled. During earthworks, the inclination angle of 40° was established. To avoid displacement and/or transport of large amounts of soil the inclination was adjusted to original slope inclination.
Fig. 3. The slope in the inoperative opencast mine Zechau; a/unstable slope; b/profiling and levelling of the slope. 3
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Fig. 5. The completion of the installation on the slope; a/the geotextiles fastened to the slope surface; b/covering of the geotextiles with the topsoil.
4. Gravel pit Nieboczowy
temperature rose above 60 °C, irrigation was activated.
4.1. Site characteristics 3.4. Slope behaviour Gravel pit Nieboczowy is located at 50°04′ N and 18°22’ E close to town Raciborz in Silesia (Poland), at the Czech-Polish border in the north part of Moravian Gate - the depression between the Carpathian Mountains in the east and the Sudetes in the west. The terrain is situated at an altitude of 200 m above sea level in temperate climate zone. The average annual temperature is 8.6 °C. The area belongs to regions with a significant rainfall with the mean annual precipitation of 659 mm. The place is located in the Upper Oder Valley, the second largest river in Poland. The valley is part of the river floodplain and is rich in sand and gravel deposits. Locally, the gravel deposits exhibit the thickness of above 10 m. Rich deposits provide a material with good characteristics, which is willingly used for road construction and production of concrete. Gravel pit Nieboczowy belonged to medium-sized gravel pits. After several years of exploitation, the deposits were exhausted and extraction of gravel was interrupted. As a result of mining deep extraction pit with the depth of approximately 15 m was formed. On the banks of the pits, steep and unstable slopes prone to local sliding and slipping were generated. The soil forming the pit banks was reach in clay and silt fraction, which amount was 32.0% and 60.3%, respectively. According to the British standard the soil was classified as CH (clay of high plasticity).
Immediately after installation the ropes arranged transversally on the slope formed a system of small retaining walls, which prevented topsoil filling the space between the ropes from sliding down the slope. As a result in the first period of exploitation during several weeks no soil movement were detected. The ropes kept topsoil on the slope and prevented its removal by wind, rain and snow. Thanks to the ropes the land sliding even by long slope and high steepness was avoided. In this way the need to build an additional retaining wall or alternatively reducing of slope inclination were eliminated. Simultaneously, additional costs connected with the necessity to displace and/or transport the large amounts of soil was avoided. In following months the topsoil was kept in the bag-like structures formed between subsequent ropes. On the slopes no further soil movements caused by sliding or water erosion were detected. The installed geotextiles provided good integration of the topsoil layer with the solid slope surface and ensured slope stability for several exploitation years. Geotextiles installed on the slope significantly contributed to its greening. The installation works on the slope were performed during summer and were finished at the end of the vegetation season. Then, in autumn and winter, the stable slope surface and lack of soil displacements prevented the seeds from leaching down the slope. In spring grass seeds sown in previous season germinated and grass covered evenly the whole surface of the slope. Rainwater absorbed inside geotextiles and the irrigation system ensured watering the grass in the initial growth phase and later greatly facilitated their further growth. Then, during the vegetation season in addition to grass, other local species appeared. The growing plants easily penetrated the geotextiles structures and in short time formed a permanent protective cover on the slope. During subsequent years in addition to herbaceous plants spontaneously grew bushes and trees appeared on the slope (Fig. 6). The bushes and trees with deep root system contributed to better slope stabilization. The installation of geotextiles solved the problem of self-ignition of the brown coal remnants. By filling the slope up with the topsoil the access of oxygen to cool remnants was restricted and by oxygen deprivation, the danger of self-ignition was reduced. At the same time, thanks to the use of an additional irrigation system, soil humidity and temperature were kept within safe limits. After several months of the system operation, self-ignition of the coal remnants was completely eliminated.
4.2. Materials For the reclamation of the gravel pit segments of ropes made from textile wastes were used. Few segments were formed from ropes made from strips of wool needle-punched nonwoven with thickness 5.8 mm and surface density 500 g/m2. Other ropes were manufactured from stitch-bonded nonwoven produced from a mixture of recycled natural and synthetic fibres. The nonwoven had the thickness 2.9 mm and surface density 300 g/m2. Certain ropes made from the recycled nonwoven was manufactured with an addition of grass seeds. The selected seed mix of perennial ryegrass (Loliumperenne) commonly used to prevent erosion and to stabilise soils was applied. The cores of the ropes were protected with the outer mesh produced from polypropylene twine with the diameter of 3 mm. The ropes with the diameter of 120 mm were obtained. The ropes possessed high water sorption capacity. For the ropes made from wool and nonwoven manufactured from recycled fibres, the absorption capacity equalled 360% and 510%, respectively. The ropes were meandrically arranged in segments with the width of 1.8 m and the length of 6 m. In order to stabilise the segments, the subsequent turns of the ropes, positioned about 0.33 m from one 4
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Fig. 6. Vegetation on the protected slope three years after the installation of the geotextiles; a/grass cover on the slope; b/scrubs spontaneously grown.
soil by raindrops. Moreover, due to their high absorption capacity, the ropes absorbed a significant portion of water. By keeping the soil from sliding, slowing down the stream of flowing water and absorbing the water, the geotextiles prevented washing out the soil particles. As a result, during several weeks of exploitation, no erosive rills nor grooves on the surface of the slope were formed and no sliding of the slope was recorded. Taking advantage of the favourable weather conditions, the geotextiles were installed at the end of the winter season. In the spring, at the beginning of the growing season the first signs of vegetation became visible on the slope. In the section protected with the ropes that contained seeds, germination and growth of grass was initiated. A few weeks later, lush tillers of perennial ryegrass (Loliumperenne) were observed (Fig. 8a). In the following weeks, tillers reached a high altitude, approximately 0.5 m. In addition to the grass grown on the ropes, other spontaneously grown plants appeared on the slope. The plants were a mixture of grasses and other common, local herbaceous plants. Seedlings of popular local species such as common dandelion (Taraxacum officinale), coltsfoot (Tussilago farfara), hedge bindweed (Calystegia sepium), compass plant (Lectuca serirola), spotted lady's thumb (Polygonum persicaria) and creeping thistle (Cirsium arvense) were identified. Later, further intensive development of plants was observed. Thus, in the summer the whole slope was covered with dense vegetation, in some places higher than 0.5 m (Fig. 8b). The dense, green cover spread uniformly on the protected part of the slope strongly contrasted with the unprotected part, where only local, sparse and randomly scattered clumps of various herbaceous plants were observed (Fig. 9). In the next spring with the beginning of new vegetation season, an intense growth of plants was initiated anew. In a short time, the slope became green and covered with lush vegetation. At the end of the spring, plants reached the high altitude locally exceeding.
another, were connected with additional linking chains made from thick polypropylene twine with a linear density 10 g/m. 4.3. Geotextile installation The geotextile segments were installed on the steepest part of the slope in a place the most exposed to land sliding. Part of the slope with length of 30 m and the total area of approximately 150 m2 was secured. The slope had the length of ca. 5 m and the inclination between 1:0.9 and 1:1.8. The inclination was adjusted to the inclination of the slope formed during gravel pit exploitation. Before the installation, the slope was profiled and levelled (Fig. 7a). Then, the segments of the geotextiles were anchored to the top of the slope, rolled out and spread on the surface of the slope. The geotextiles were fastened with steel “U-shaped” pins made from ribbed bars of diameters φ = 8 mm. The subsequent geotextile segments were laid next to one another to cover the entire protected area (Fig. 7b). Following the fastening of the geotextiles, the slope was covered with the 20 cm layer of locally available soil taken from the overburden of the deposit. The content of clay and silt fraction of topsoil was similar to the soil forming the slope. The content of organic matter equalled 1.4%. The soil did not contain additional fertilizers. During installation of ropes, no additional amending promoting plant growth nor compost were applied. 4.4. Slope behaviour In the first period of exploitation, the geotextiles prevented local gravitational landslides of topsoil poorly integrated with the native ground. Simultaneously, the settlement of the soil particles covering the geotextiles was observed. During rains, the ropes arranged laterally on the slope formed a network of micro-dams, which slowed down the flow of water and reduced the transport of materials detached from the
Fig. 7. Installation of geotextiles; a/profiling and levelling of the slope; b/spreading and fixing of geotextiles segments on the surface of the slope. 5
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Fig. 8. Greening of the slope; a/grass grown on the ropes; b/dense vegetation on the slope in summer.
cover on the whole surface, both in the lower and upper part of the slope. By absorbing water ropes provided the moist environment for seeds germination and later adequate moisture around the root system, guaranteeing favourable conditions for further plant growth. Ropes absorbed excess water during melting of snow and heavy rainfalls. Absorbed water was stored inside ropes and then slowly released into the soil. In this way, ropes provided a supply of water during droughts and enabled plants growth without additional irrigation. Due to the positive impact of ropes on plants growth, the greening of slopes was achieved on slopes covered with topsoil poor in organic matter and lack of nutrients supporting plant growth. The effect was obtained without application of fertilizers and additional soil amendments. Ropes considerably accelerated slope greening and enabled the formation of dense and rich green cover in few years. In lignite openmine vegetation was established on the slope, on which vegetation formation via spontaneous process was for many years impossible. In this case, the growth of plants was initiated on grass seeds sown just after ropes installation. Grasses, which are usually considered as a nurse crop for an early vegetation purpose contributed to soil stabilization. Fibrous roots of grasses slowed erosion and favoured formation of a layer of soil reach in organic matter. Grasses provided conditions for further development of other herbaceous species, which growth was followed in the spontaneous process. After a few years in addition to grass and herbaceous plants on the slope spontaneously, various shrubs and trees appeared. In the gravel pit, the dense vegetation cover formed from various local herbaceous species, typical for the first stage of the spontaneous ecological succession, grew spontaneously already in first vegetation season. Indigenous species developed on the slope were climatically adapted and well fit into the local ecosystem. During the following three years the total species number, their richness and coverage were significantly increased. Through the use of ropes, the rich vegetation was achieved only in three years. In similar
1 m and formed a very dense, uniform cover on the whole surface of the slope. During the blooming period in June, a variety of differently coloured flowers were observed. In comparison to the previous years, the vegetation cover on the slope was much denser. In June, apart from the species observed in the previous year, more than twenty other species were identified. From twenty-nine various species identified on the slope three species: Tussilago farfara, Lactuca serirola and Calystegia sepium were found in different places on the whole protected area. Among these species, coltsfoot Tussilago farfara evidently dominated and covered approximately 50% of the surface of the slope. 5. Discussion Geotextiles made from the meandrically arranged ropes manufactured by Kemafil technology were successfully used for reclamation of abandoned open mines. After installation, the geotextiles reduced movement of soil particles on the slope surface. The subsequent turns of meandrically arranged ropes formed on slopes a system of small retaining walls, which prevented topsoil from sliding down the slope. Additionally, during rains ropes partially retained water and significantly reduced its runoff on the slope surface. In this way ropes inhibit displacement of soil particles by surface erosion. Both mechanisms, diminishing land sliding and water erosion, contributed to the stabilization of steep and denuded slopes and provided their sufficient protection prior to the development of vegetation. Restriction of soil particles movements created a stable base both for seeds germination and plant growth. Ropes sufficiently eliminated slope collapse and formation on the slope erosion rills and local cracks, what minimalized mechanical rupture of seedlings or plants roots. Moreover, ropes by reducing water runoff inhibited leaching of plant seeds and nutrients supporting plants growth. In this situation plants grown from seeds evenly distributed in the soil formed a dense green
Fig. 9. The unprotected part of the slope; a/rare and scattered vegetation b/local land sliding of the slope. 6
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circumstances without geotextiles reaching such a stage of vegetation in spontaneous process took several years.
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6. Conclusions The geotextiles formed from thick ropes arranged in the meanderlike pattern have proven to be an effective measure for reclamation of abandoned open mines. The ropes made from textile materials provided stabilization of slopes generated during mining and considerably accelerated restoration of vegetation. The ropes transversally installed on steep slopes effectively eliminated their sliding and reduced an impact of water erosion. By stabilising the slope and improving water management the ropes provided favourable conditions for seeds germination and accelerated further plants growth. In unfavourable terrain conditions, the geotextiles enabled quick greening of the closed mines and formation of vegetation with great ecological value. In the case of lignite mine, application of the geotextiles coupled with additional irrigation system eliminated the self-ignition of the coal remnants. Acknowledgements The authors gratefully acknowledge the funding by ERANETCORNET consortium under the international research project PROGEO 2 “Geotextiles from Sustainable Raw Materials and Textile Waste, New Mobile Production Technology and New Application Fields in Drainage and Hydraulic Engineering”. DZP/CORNET/1/20/2017. References Ahn, T.B., Cho, S.D., Yang, S.C., 2002. Stabilization of soil slope uising geosynthetic mulching mat. Geotext. Geomembranes 20, 135–146. Arnold, R., Bartl, A.-M., Hufnagl, E., 1993. Production of cord and narrow fabric products with Kemafil technology. Band- Flechtind. 1, 4–10. Arnold, R., Bartl, A.-M., Hufnagl, E., 1995. Recycling approach using the Kemafil technology. Tech. Text. 39 (1), 24–28. Baasch, A., Kirmer, A., Tischew, S., 2012. Nine years of vegetation development in a postmining site: effects of spontaneous and assisted site recovery. J. Appl. Ecol. 49, 251–260. Baxter, R., 2008. Wattles and other sediment control devices. Eros. Control 15, 44–51. Berthold, M., Arnold, R., 1975. Patent DD 110 905. Borgegård, S., 1990. Vegetation development in abandoned gravel pits: effects of surrounding vegetation, substrate and regionality. J. Veg. Sci. 1, 675–682. Bradshaw, A., 1997. Restoration of mined lands—using natural processes. Ecol. Eng. 8, 255–269. Bradshaw, A., 2000. The use of natural processes in reclamation - advantages and difficulties. Landsc. Urban Plan. 51, 89–100. Bradshaw, A.D., Chadwick, M.J., 1980. The Restoration of Land: the Ecology and Reclamation of Derelict and Degraded Land. Blackwell Scientific Publications, Oxford. Broda, J., Gawlowski, A., Rom, M., Laszczak, R., Mitka, A., Przybyło, S., GrzybowskaPietras, J., 2016. Innovative geotextiles for reinforcement of roadside ditch. Tekstilec 59, 115–120. Broda, J., Gawlowski, A., Laszczak, R., Mitka, A., Przybylo, S., Grzybowska-Pietras, J., Rom, M., 2017. Application of innovative meandrically arranged geotextiles for the protection of drainage ditches in the clay ground. Geotext. Geomembranes 45, 45–53. Broda, J., Gawlowski, A., Przybylo, S., Binias, D., Rom, M., Grzybowska-Pietras, J., Laszczak, R., 2018. Innovative wool geotextiles designed for erosion protection. J. Ind. Text. 48 (3) 599–61. Carroll, R.G., Rodencal, J., Collin, J.G., 1992. Geosynthetics in erosion control — the principles. Geotext. Geomembranes 11 (4–6), 523–534. Etra, J., 2011. Fiber roles or sediment logs: the rest of the story. Environ. Conn. 5, 20–21. García, C.B., Monical, J., Bhattarai, R., Kalita, P.K., 2015. Field evaluation of sediment retention devices under concentrated flow conditions. J. Soils Sediments 15,
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Technical note
Reclamation of abandoned open mines with innovative meandrically arranged geotextiles Jan Brodaa,∗, Petra Franitzab, Ulrich Herrmannb, Reinhard Helbigb, Anna Großeb, Joanna Grzybowska-Pietrasa, Monika Roma a b
Institute of Textile Engineering and Polymer Materials, University of Bielsko-Biala, Bielsko-Biala, Poland Saxon Textile Research Institute, Chemnitz, Germany
A R T I C LE I N FO
A B S T R A C T
Keywords: Geosynthetics Open mine reclamation Kemafil technology Vegetation restoration
For over fifty years, geosynthetics have been used for land reclamation of degraded areas. Several years ago for this purpose innovative geotextiles formed from meandrically arranged thick ropes were invented. The geotextiles were used for reclamation of abandoned lignite open-mine in Germany and disused gravel pit in Poland. The geotextiles were installed in abandoned mines. In next years positive influence of geotextiles on slopes behaviour and vegetation was observed. It was stated that the geotextiles provide stabilization of steep unstable slopes and significantly accelerate vegetation development. The innovative geotextiles perform functions unobtainable for other traditional products. The products are useful in an effective reclamation of open mines and constitute a valuable extension of the geosynthetic assortment applicable in land reclamation.
1. Introduction For many years opencast mining is a commonly used for extraction of brown coal, ore, sand, gravel and other mineral resources. Extraction of mineral deposits shallowly located under the land surface is efficient and cost-effective. Nevertheless, the process generates considerably environmental problems and has a severe negative impact on a surrounding landscape and other elements of the local ecosystem. Intensive mining leads to land degradation, which after closing the mine, requires satisfactory restoration. Usually, restoring of degraded land to its original state is difficult and economically unreasonable. In this situation degraded post-mining areas are subject to reclamation, which ends up in a new state where the structure or function of the land is different from the original. The effective reclamation requires a series of measures to protect unstable slopes and restore the vegetation. Vegetation has an important role in protecting the soil surface from erosion. Plants grew on the slope decrease soil bulk density, moderate soil pH, increase soil organic matter and accumulate mineral nutrients in the layer closed to the soil surface. Additionally, on a macro scale vegetation restores the beauty and productivity of the land (Schor and Gray, 2007; Hutnik and McKee, 1990). For the above reasons, the re-establishing of vegetation is a major challenge and a key indicator of reclamation success (Sheoran et al., 2010).
∗
Due to physical and biological conditions unfavourable for plant growth, re-establishing of vegetation may be difficult. The growth of the plant cover can be constrained by improper soil structure and its inadequate particles size distribution, water shortage, gross lack of certain nutrients and soil toxicity (Peris et al., 2017). Re-establishing of vegetation may be extremely hard in a dry climate and on steep slopes endangered by severe erosion (Moreno-de las Heras et al., 2008; Moreno-de las Heras et al., 2009). In temperate climate re-establishment of vegetation may occur as a result of a spontaneous process. Species colonized through spontaneous succession are well adapted to local site conditions, exhibit higher diversity and possess greater natural value. Nevertheless, reaching the target state of spontaneously grown vegetation is a long-term process and often takes several years (Borgegård, 1990; Rehounkova and Prach, 2008; Prach et al., 2013; Prach et al., 2014). To accelerate vegetation development in degraded land different techniques can be applied (Bradshaw and Chadwick, 1980; Bradshaw, 1997, 2000; Kiehl et al., 2010; Baasch et al. 2012; Kuter, 2013; Mudrák et al., 2016). One method, commonly used for several years consists on an application of geosynthetics (Theisen, 1992; Kumar and Das, 2018; Ngo et al., 2019; Nsiah and Schaaf, 2019). A wide assortment of geosynthetics suitable for mines reclamation includes erosion control products, such as mats and blankets, which are installed in a very close contact with the ground surface (Ogdobe et al.
Corresponding author. E-mail address: [email protected] (J. Broda).
https://doi.org/10.1016/j.geotexmem.2019.11.003 Received 28 August 2018; Received in revised form 19 November 2019; Accepted 19 November 2019 0266-1144/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Jan Broda, et al., Geotextiles and Geomembranes, https://doi.org/10.1016/j.geotexmem.2019.11.003
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1998; Ahn et al. 2002; Shao et al., 2014; Prambauer et al., 2019). The second group of products includes three-dimensional turf-reinforcement mats, which are designed to be seeded and then filled with the soil (Carroll et al., 1992; Weggel and Rustom, 1992; Wu and Austin, 1992; Pritchard et al., 2000; Rickson, 2006; Shukla, 2016). In addition to such products for the reclamation of mines flexible fibre rolls may be adapted. Rolls are tube-shaped devices filled with straw, rice husks, flax, coconut fibres or other organic composting material wrapped in a netting made from natural or synthetic polymer materials (Etra, 2011). Certain products are formed from blankets rolled into large diameter logs. Depending on their destination, the rolls with various length and diameters can be produced. The rolls are installed on the slopes in dug shallow trenches at a depth equal to half of the diameter of the log and hold in place by wooden stakes. Flexible rolls can be bent along the contours of the land and can be coiled into a circle (Baxter, 2008). The rolls installed transversally on the slopes form a system of micro-dams, which breaks up the slopes and reduces the velocity of water flowing on the surface (García et al., 2015). Several years ago for the production of fibre rolls the Kemafil technology was applied (Berthold and Arnold, 1975; Helbig et al., 2006a). In initial tests, ropes with the diameter of 50 mm were obtained. The ropes made from textile waste were applied for the protection of banks of an expansion tank and sandy roadside slopes. In the protected places, straight ropes were diagonally spread on the slopes to form squares of 60–70 cm and fastened to the ground with metal anchors. Following the installation, the grid formed by the ropes was covered with soil and sown with grass seeds. It was revealed that the grid made from the ropes effectively protects the slopes and positively affects plant vegetation. In the next studies thicker ropes, with the diameter of up to 130 mm, were manufactured. The ropes were arranged in a meanderlike pattern to form bigger segments. To stabilise the segments, the subsequent turns of ropes were connected with additional linking chains (Helbig et al., 2006b). The meandrical arrangement ensured the high mechanical strength of the segments both, longwise and crosswise. The segments formed from meandrically arranged ropes were successfully used for the protection of road embankments and drainage ditches (Broda et al. 2016, 2017, 2018). In further studies, segments were used for reclamation of abandoned open-mines. The ropes were installed on a steep and unstable slope in disused lignite pit mine in eastern Germany as well as on steep slope in the abandoned gravel pit in southern Poland. In the paper, the installation of ropes is presented. The stability of slopes and their greening during several years of exploitation is analysed. The effectiveness of ropes in the reclamation of disused mines is evaluated and their role in slopes stabilization and vegetation development is explained.
Fig. 1. Kemafil technology: a/the guiding tube and the loopers; b/the rope.
levelled slope, anchored to the top of the slope and fastened to its surface with steel “U-shaped” pins. Later the segments were covered with a layer of topsoil. After geotextiles installation stability of slopes and their greening were regularly monitored. During three vegetation seasons, potential soil movements, as well as erosion rills and gullies, were observed. An impact of geotextiles on land sliding and surface erosion was qualitatively assessed. Simultaneously, development of vegetation on the protected slopes was analysed. During observations intensity of green cover in particular vegetation seasons was analysed. Moreover, the plant species appeared on the slopes were identified and their range of cover was estimated. 3. Opencast lignite mine Zechau 3.1. Site characteristics The inoperative opencast lignite mine Zechau is located at 51°00′ N and 12°19’ E in the north-west part of the Thuringian district – Altenburger Land, between the cities Meuselwitz and Altenburg (Germany). The terrain is situated at an altitude of 230 m above sea level in temperate climate zone. The average annual temperature for this place equals 8.6 °C, while the mean annual precipitation is 551 mm. For more than 100 years, an extensive opencast lignite mining was carried out in the region. Mining has profoundly transformed the landscape and led to a significant change of various environmental components. After the closure of the mines, in order to make the large areas suitable for agriculture, forestry and nature conservational activities, the former lignite mining facilities were reclaimed. The main task was to integrate the reclaimed lands into the surrounding landscapes and to restore the populations of flora and fauna. Zechau opencast brown coal mine was opened in 1931 and closed after 28 years of operation in 1959. The excavation site with the surface area of approximately 4.5 km2 was partially filled with water. In the following years, the area became part of the European nature protection zone Natura 2000. The reserve Restloch Zechau with the surface area of 213 ha gained the status of the protected area in 2000 and became the habitat for rare species of animals and plants (Fig. 2) (Krummsdorf et al., 1998). After the closure of the mine, a deep hole with steep slopes remained on the site. The denuded slopes formed from sandy soil mixed with brown coal remnants were prone to local sliding (Fig. 3). Additionally, the brown coal deposits exposed to high solar radiation, especially on the southwest side, had a tendency to self-ignite. As a result, the slopes were often on fire, emitting irritating odours and smoke. Frequently smouldering slopes became unbearable for the local residents.
2. Materials and methods For reclamation of abandoned mines geotextiles formed from thick ropes were applied. The ropes were manufactured from textile materials, nonwovens made from biodegradable natural fibres and nonbiodegradable synthetic fibres. A part of the ropes was produced from recycled fibres obtained by shredding of post-consumer textile wastes. For the production of ropes, the Kemafil technology was applied. The technology involves use of a small circular knitting machine, which is equipped with four hooked loopers arranged around the guiding tube (Fig. 1a). The threads guided by the loopers from a tubular sheath around the thick rope core (Fig. 1b) (Arnold et al., 1993, 1995). The ropes were arranged into a meander-like pattern to form twodimensional flat segments. Inside segments the ropes were connected with additional linking chains. Dimensions of segments, a distance between the successive turns of the ropes as well as the number and the distribution of transverse links were adapted to terrain conditions. Segments were rolled up and transported to the installation site. Then they were rolled out and unfolded on the surface of the profiled and 2
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Fig. 2. Inoperative excavation of the lignite mine Zechau; a/the hole filled with water.
3.2. Materials For reclamation of the lignite mine, coarse Kemafil ropes with the diameter of 120 mm were produced. As rope filling material voluminous stitch-bonded polyester nonwoven with good water storage properties was applied. The nonwoven was manufactured by Maliwatt technology and had thickness 3 mm and surface density 200 g/m2. The core of the ropes was wrapped with a covering spun-laced polyester nonwoven with thickness 1 mm and surface density 80 g/m2. The ropes were sheathed with a mesh made from polypropylene multifilament with the thickness of 220 tex. In the central part of the ropes a perforated irrigation tube with the outer diameter φ = 12 mm was inserted (Fig. 4). The ropes were used to form 1.8 m wide and 20 m long meandrically arranged segments. The links between the subsequent turns of the ropes were made with a hybrid thread that was composed of polyethylene tapes (18 cm width and 0.2 mm thick) and high-density polypropylene threads (18 filaments, each 220 tex). To avoid kinking of the irrigation tubes placed inside the ropes the optimal interval of 0.6 m between the rope-meanders was established. To improve the settlement of the topsoil between the meanders, additional thinner ropes without irrigation tube were mounted.
Fig. 4. The structure of the Kemafil rope with the integrated irrigation tube.
After preparatory works and slope levelling the rolled segments of the geotextiles were placed on the crown of the slope. Subsequently, the segments were fixed on the top shelf and then rolled down the slope. The ropes were fastened to the slope with the U-shaped soil nails fabricated from steel ribbed bars with the length of 60 cm and the diameter φ = 10 mm. Finally, the geotextiles were covered with a 15 cm layer of weakly binding humus soil (Fig. 5). According to DIN 18915:2002–08 the soil, so-called German Kulturboden, belongs to floor group 4, possesses pH 5,0–5,5 and consists of 15–20% slurriable particles, 10–15% coarse soil and 3–4% humus. Once covered, the slope was seeded with a mixture of grass seeds, e.g. festuca ovina duriuscula, festuca rubra commutata, festuca rubra rubra and festuca rubra trichophylla, usually used for reclamation, greening and stabilising light soils to guard against erosion. During installation, the geotextiles were combined with irrigation and monitoring systems and coupled with the local public water supply source. The system was divided into 12 watering circuits, which were steered by impulse controlled solenoid coils. Irrigation was activated three times a day, for 30 min each time. Additionally, the integrated temperature and humidity sensors were connected to the irrigation control system. If the humidity dropped below 50% or the soil
3.3. Geotextiles installation The denuded slope prone to land sliding located on the southwest side of the pit with the total length of 200 m and area of 4000 m2 was protected. The average height of the slope was 10 m and its inclination length equalled 20.5–21.5 m. Before installation of geotextiles, the slope was profiled and levelled. During earthworks, the inclination angle of 40° was established. To avoid displacement and/or transport of large amounts of soil the inclination was adjusted to original slope inclination.
Fig. 3. The slope in the inoperative opencast mine Zechau; a/unstable slope; b/profiling and levelling of the slope. 3
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Fig. 5. The completion of the installation on the slope; a/the geotextiles fastened to the slope surface; b/covering of the geotextiles with the topsoil.
4. Gravel pit Nieboczowy
temperature rose above 60 °C, irrigation was activated.
4.1. Site characteristics 3.4. Slope behaviour Gravel pit Nieboczowy is located at 50°04′ N and 18°22’ E close to town Raciborz in Silesia (Poland), at the Czech-Polish border in the north part of Moravian Gate - the depression between the Carpathian Mountains in the east and the Sudetes in the west. The terrain is situated at an altitude of 200 m above sea level in temperate climate zone. The average annual temperature is 8.6 °C. The area belongs to regions with a significant rainfall with the mean annual precipitation of 659 mm. The place is located in the Upper Oder Valley, the second largest river in Poland. The valley is part of the river floodplain and is rich in sand and gravel deposits. Locally, the gravel deposits exhibit the thickness of above 10 m. Rich deposits provide a material with good characteristics, which is willingly used for road construction and production of concrete. Gravel pit Nieboczowy belonged to medium-sized gravel pits. After several years of exploitation, the deposits were exhausted and extraction of gravel was interrupted. As a result of mining deep extraction pit with the depth of approximately 15 m was formed. On the banks of the pits, steep and unstable slopes prone to local sliding and slipping were generated. The soil forming the pit banks was reach in clay and silt fraction, which amount was 32.0% and 60.3%, respectively. According to the British standard the soil was classified as CH (clay of high plasticity).
Immediately after installation the ropes arranged transversally on the slope formed a system of small retaining walls, which prevented topsoil filling the space between the ropes from sliding down the slope. As a result in the first period of exploitation during several weeks no soil movement were detected. The ropes kept topsoil on the slope and prevented its removal by wind, rain and snow. Thanks to the ropes the land sliding even by long slope and high steepness was avoided. In this way the need to build an additional retaining wall or alternatively reducing of slope inclination were eliminated. Simultaneously, additional costs connected with the necessity to displace and/or transport the large amounts of soil was avoided. In following months the topsoil was kept in the bag-like structures formed between subsequent ropes. On the slopes no further soil movements caused by sliding or water erosion were detected. The installed geotextiles provided good integration of the topsoil layer with the solid slope surface and ensured slope stability for several exploitation years. Geotextiles installed on the slope significantly contributed to its greening. The installation works on the slope were performed during summer and were finished at the end of the vegetation season. Then, in autumn and winter, the stable slope surface and lack of soil displacements prevented the seeds from leaching down the slope. In spring grass seeds sown in previous season germinated and grass covered evenly the whole surface of the slope. Rainwater absorbed inside geotextiles and the irrigation system ensured watering the grass in the initial growth phase and later greatly facilitated their further growth. Then, during the vegetation season in addition to grass, other local species appeared. The growing plants easily penetrated the geotextiles structures and in short time formed a permanent protective cover on the slope. During subsequent years in addition to herbaceous plants spontaneously grew bushes and trees appeared on the slope (Fig. 6). The bushes and trees with deep root system contributed to better slope stabilization. The installation of geotextiles solved the problem of self-ignition of the brown coal remnants. By filling the slope up with the topsoil the access of oxygen to cool remnants was restricted and by oxygen deprivation, the danger of self-ignition was reduced. At the same time, thanks to the use of an additional irrigation system, soil humidity and temperature were kept within safe limits. After several months of the system operation, self-ignition of the coal remnants was completely eliminated.
4.2. Materials For the reclamation of the gravel pit segments of ropes made from textile wastes were used. Few segments were formed from ropes made from strips of wool needle-punched nonwoven with thickness 5.8 mm and surface density 500 g/m2. Other ropes were manufactured from stitch-bonded nonwoven produced from a mixture of recycled natural and synthetic fibres. The nonwoven had the thickness 2.9 mm and surface density 300 g/m2. Certain ropes made from the recycled nonwoven was manufactured with an addition of grass seeds. The selected seed mix of perennial ryegrass (Loliumperenne) commonly used to prevent erosion and to stabilise soils was applied. The cores of the ropes were protected with the outer mesh produced from polypropylene twine with the diameter of 3 mm. The ropes with the diameter of 120 mm were obtained. The ropes possessed high water sorption capacity. For the ropes made from wool and nonwoven manufactured from recycled fibres, the absorption capacity equalled 360% and 510%, respectively. The ropes were meandrically arranged in segments with the width of 1.8 m and the length of 6 m. In order to stabilise the segments, the subsequent turns of the ropes, positioned about 0.33 m from one 4
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Fig. 6. Vegetation on the protected slope three years after the installation of the geotextiles; a/grass cover on the slope; b/scrubs spontaneously grown.
soil by raindrops. Moreover, due to their high absorption capacity, the ropes absorbed a significant portion of water. By keeping the soil from sliding, slowing down the stream of flowing water and absorbing the water, the geotextiles prevented washing out the soil particles. As a result, during several weeks of exploitation, no erosive rills nor grooves on the surface of the slope were formed and no sliding of the slope was recorded. Taking advantage of the favourable weather conditions, the geotextiles were installed at the end of the winter season. In the spring, at the beginning of the growing season the first signs of vegetation became visible on the slope. In the section protected with the ropes that contained seeds, germination and growth of grass was initiated. A few weeks later, lush tillers of perennial ryegrass (Loliumperenne) were observed (Fig. 8a). In the following weeks, tillers reached a high altitude, approximately 0.5 m. In addition to the grass grown on the ropes, other spontaneously grown plants appeared on the slope. The plants were a mixture of grasses and other common, local herbaceous plants. Seedlings of popular local species such as common dandelion (Taraxacum officinale), coltsfoot (Tussilago farfara), hedge bindweed (Calystegia sepium), compass plant (Lectuca serirola), spotted lady's thumb (Polygonum persicaria) and creeping thistle (Cirsium arvense) were identified. Later, further intensive development of plants was observed. Thus, in the summer the whole slope was covered with dense vegetation, in some places higher than 0.5 m (Fig. 8b). The dense, green cover spread uniformly on the protected part of the slope strongly contrasted with the unprotected part, where only local, sparse and randomly scattered clumps of various herbaceous plants were observed (Fig. 9). In the next spring with the beginning of new vegetation season, an intense growth of plants was initiated anew. In a short time, the slope became green and covered with lush vegetation. At the end of the spring, plants reached the high altitude locally exceeding.
another, were connected with additional linking chains made from thick polypropylene twine with a linear density 10 g/m. 4.3. Geotextile installation The geotextile segments were installed on the steepest part of the slope in a place the most exposed to land sliding. Part of the slope with length of 30 m and the total area of approximately 150 m2 was secured. The slope had the length of ca. 5 m and the inclination between 1:0.9 and 1:1.8. The inclination was adjusted to the inclination of the slope formed during gravel pit exploitation. Before the installation, the slope was profiled and levelled (Fig. 7a). Then, the segments of the geotextiles were anchored to the top of the slope, rolled out and spread on the surface of the slope. The geotextiles were fastened with steel “U-shaped” pins made from ribbed bars of diameters φ = 8 mm. The subsequent geotextile segments were laid next to one another to cover the entire protected area (Fig. 7b). Following the fastening of the geotextiles, the slope was covered with the 20 cm layer of locally available soil taken from the overburden of the deposit. The content of clay and silt fraction of topsoil was similar to the soil forming the slope. The content of organic matter equalled 1.4%. The soil did not contain additional fertilizers. During installation of ropes, no additional amending promoting plant growth nor compost were applied. 4.4. Slope behaviour In the first period of exploitation, the geotextiles prevented local gravitational landslides of topsoil poorly integrated with the native ground. Simultaneously, the settlement of the soil particles covering the geotextiles was observed. During rains, the ropes arranged laterally on the slope formed a network of micro-dams, which slowed down the flow of water and reduced the transport of materials detached from the
Fig. 7. Installation of geotextiles; a/profiling and levelling of the slope; b/spreading and fixing of geotextiles segments on the surface of the slope. 5
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Fig. 8. Greening of the slope; a/grass grown on the ropes; b/dense vegetation on the slope in summer.
cover on the whole surface, both in the lower and upper part of the slope. By absorbing water ropes provided the moist environment for seeds germination and later adequate moisture around the root system, guaranteeing favourable conditions for further plant growth. Ropes absorbed excess water during melting of snow and heavy rainfalls. Absorbed water was stored inside ropes and then slowly released into the soil. In this way, ropes provided a supply of water during droughts and enabled plants growth without additional irrigation. Due to the positive impact of ropes on plants growth, the greening of slopes was achieved on slopes covered with topsoil poor in organic matter and lack of nutrients supporting plant growth. The effect was obtained without application of fertilizers and additional soil amendments. Ropes considerably accelerated slope greening and enabled the formation of dense and rich green cover in few years. In lignite openmine vegetation was established on the slope, on which vegetation formation via spontaneous process was for many years impossible. In this case, the growth of plants was initiated on grass seeds sown just after ropes installation. Grasses, which are usually considered as a nurse crop for an early vegetation purpose contributed to soil stabilization. Fibrous roots of grasses slowed erosion and favoured formation of a layer of soil reach in organic matter. Grasses provided conditions for further development of other herbaceous species, which growth was followed in the spontaneous process. After a few years in addition to grass and herbaceous plants on the slope spontaneously, various shrubs and trees appeared. In the gravel pit, the dense vegetation cover formed from various local herbaceous species, typical for the first stage of the spontaneous ecological succession, grew spontaneously already in first vegetation season. Indigenous species developed on the slope were climatically adapted and well fit into the local ecosystem. During the following three years the total species number, their richness and coverage were significantly increased. Through the use of ropes, the rich vegetation was achieved only in three years. In similar
1 m and formed a very dense, uniform cover on the whole surface of the slope. During the blooming period in June, a variety of differently coloured flowers were observed. In comparison to the previous years, the vegetation cover on the slope was much denser. In June, apart from the species observed in the previous year, more than twenty other species were identified. From twenty-nine various species identified on the slope three species: Tussilago farfara, Lactuca serirola and Calystegia sepium were found in different places on the whole protected area. Among these species, coltsfoot Tussilago farfara evidently dominated and covered approximately 50% of the surface of the slope. 5. Discussion Geotextiles made from the meandrically arranged ropes manufactured by Kemafil technology were successfully used for reclamation of abandoned open mines. After installation, the geotextiles reduced movement of soil particles on the slope surface. The subsequent turns of meandrically arranged ropes formed on slopes a system of small retaining walls, which prevented topsoil from sliding down the slope. Additionally, during rains ropes partially retained water and significantly reduced its runoff on the slope surface. In this way ropes inhibit displacement of soil particles by surface erosion. Both mechanisms, diminishing land sliding and water erosion, contributed to the stabilization of steep and denuded slopes and provided their sufficient protection prior to the development of vegetation. Restriction of soil particles movements created a stable base both for seeds germination and plant growth. Ropes sufficiently eliminated slope collapse and formation on the slope erosion rills and local cracks, what minimalized mechanical rupture of seedlings or plants roots. Moreover, ropes by reducing water runoff inhibited leaching of plant seeds and nutrients supporting plants growth. In this situation plants grown from seeds evenly distributed in the soil formed a dense green
Fig. 9. The unprotected part of the slope; a/rare and scattered vegetation b/local land sliding of the slope. 6
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circumstances without geotextiles reaching such a stage of vegetation in spontaneous process took several years.
2022–2031. Helbig, R., Arnold, R., Erth, H., 2006a. Knitted structures for applications as geosynthetics or in agriculture and horticulture. Tech. Text. 49 (3), 187–189 142. Helbig, R., Arnold, R., Erth, H., Roess, T., Hevert, W., Lischkowitz, H., 2006b. New technologies for manufacturing extra coarse rope-like biodegradable geotextiles. Tech. Text. 49, 185–187 244-247. Hutnik, R.J., McKee, G.W., 1990. Revegation. In: Kennedy, B.A. (Ed.), Surface Mining. Port City Press, Baltimore USA. Kiehl, K., Kirmer, A., Donath, T.W., Rasran, L., Holzel, N., 2010. Species introduction in restoration projects – evaluation of different techniques for the establishment of seminatural grasslands in Central and Northwestern Europe. Basic Appl. Ecol. 11, 285–299. Krummsdorf, A., Höser, N., Sykora, W., 1998. NaturschutzgebietTagebauZechauimKreis Altenburg in thüringen. In: Pflug, W. (Ed.), the book: Braunkohlentagebau und Rekultivierung. Landschaftsökologie — Folgenutzung — Naturschutz. SpringerVerlag Berlin Heidelberg, pp. 916–925 Chapter in. Kumar, N., Das, D., 2018. Nonwoven geotextiles from nettle and poly(lactic acid) fibers for slope stabilization using bioengineering approach. Geotext. Geomembranes 46, 206–213. Kuter, N., 2013. Reclamation of degraded landscapes due to opencast mining. In: Özyavuz, Murat (Ed.), Advances in Landscape Architecture. InTech Rijeka. Moreno-de las Heras, M., Nicolau, J.M., Espigares, T., 2008. Vegetation succession in reclaimed coal-mining slopes in a Mediterranean-dry environment. Ecol. Eng. 34, 168–178. Moreno-de las Heras, M., Merino-Martín, L., Nicolau, J.M., 2009. Effect of vegetation cover on the hydrology of reclaimed mining soils under Mediterranean-Continental climate. Catena 77, 39–47. Mudrák, O., Doležal, J., Frouz, J., 2016. Initial species composition predicts the progress in the spontaneous succession on post-mining sites. Ecol. Eng. 95, 665–670. Ngo, T.P., Likitlersuang, S., Takahashi, A., 2019. Performance of a geosynthetic cementitious composite mat for stabilising sandy slopes. Geosynth. Int. 26, 309–319. Nsiah, P.K., Schaaf, W., 2019. The potentials of biological geotextiles in erosion and sediment control during gold mine reclamation in Ghana. J. Soils Sediments 19, 1995–2006. Ogbobe, O., Essien, K.S., Adebayo, A., 1998. A study of biodegradable geotextiles used for erosion control. Geosynth. Int. 5 (5), 545–553. Peris, P.M., Gómez, J.C., Herbert, J.H., Fraileb, D.B., 2017. Ecological restoration of a former gravel pit contaminated by a massive petroleum sulfonate spill. A case study: arganda del Rey.Madrid (Spain). Ecol. Eng. 100, 73–88. Prach, K., Lencová, K., Řehounková, K., Dvořáková, H., Jírová, A., Konvalinková, P., Mudrák, O., Novák, J., Trnková, J., 2013. Spontaneous vegetation succession at different central European mining sites: a comparison across seres. Environ. Sci. Pollut. Control Ser. 20, 7680–7685. Prach, K., Řehounkova, K., Lencova, K., Jírova, A., Konvalinková, P., Mudrák, O., Student, V., Vanecek, Z., Tichy, L., Petrık, P., Smilauer, P., Pysek, P., 2014. Vegetation succession in restoration of disturbed sites in Central Europe: the direction of succession and species richness across 19 seres. Appl. Veg. Sci. 17, 193–200. Prambauer, M., Wendeler, C., Weitzenböck, J., Burgstaller, C., 2019. Biodegradable geotextiles – an overview of existing and potential materials. Geotext. Geomembranes 47, 48–59. Pritchard, M., Sarsby, R.W., Anand, S.C., 2000. Textiles in civil engineering. Part 2 – natural fibre geotextiles. In: Horrocks, A.R., Anand, S.C. (Eds.), Handbook of Technical Textiles. Woodhead Publishing, Cambridge, pp. 372–406. Rehounkova, K., Prach, K., 2008. Spontaneous vegetation succession in gravel–sand pits: a potential for restoration. Restor. Ecol. 16, 305–331. Rickson, R.J., 2006. Controlling sediment at source: an evaluation of erosion control geotextiles. Earth Surf. Process. Landforms 31, 550–560. Schor, H.J., Gray, D.H., 2007. Landforming: an Environmental Approach to Hillside Development, Mine Reclamation and Watershed Restoration. John Wiley & Sons. Shao, Q., Gua, W., Dai, Q., Makoto, S., Liu, Y., 2014. Effectiveness of geotextile mulches for slope restoration in semi-aridnorthern China. Catena 116, 1–9. Sheoran, V., Sheoran, A.S., Poonia, P., 2010. Soil reclamation of abandoned mine land by revegetation: a review. Int. J. Soil Sediment Water 3, 1–20. Shukla, S.K., 2016. An Introduction to Geosynthetic Engineering. CRC Press, Taylor and Francis Group, London. Theisen, M.S., 1992. The role of geosynthetics in erosion and sediment control: an overview. Geotext. Geomembranes 11 (4–6), 535–550. Weggel, J.R., Rustom, R., 1992. Soil erosion by rainfall and runoff—state of the art. Geotext. Geomembranes 11 (4–6), 551–572. Wu, K.J., Austin, D.N., 1992. Three-dimensional polyethylene geocells for erosion control and channel linings. Geotext. Geomembranes 11, 611–620.
6. Conclusions The geotextiles formed from thick ropes arranged in the meanderlike pattern have proven to be an effective measure for reclamation of abandoned open mines. The ropes made from textile materials provided stabilization of slopes generated during mining and considerably accelerated restoration of vegetation. The ropes transversally installed on steep slopes effectively eliminated their sliding and reduced an impact of water erosion. By stabilising the slope and improving water management the ropes provided favourable conditions for seeds germination and accelerated further plants growth. In unfavourable terrain conditions, the geotextiles enabled quick greening of the closed mines and formation of vegetation with great ecological value. In the case of lignite mine, application of the geotextiles coupled with additional irrigation system eliminated the self-ignition of the coal remnants. Acknowledgements The authors gratefully acknowledge the funding by ERANETCORNET consortium under the international research project PROGEO 2 “Geotextiles from Sustainable Raw Materials and Textile Waste, New Mobile Production Technology and New Application Fields in Drainage and Hydraulic Engineering”. DZP/CORNET/1/20/2017. References Ahn, T.B., Cho, S.D., Yang, S.C., 2002. Stabilization of soil slope uising geosynthetic mulching mat. Geotext. Geomembranes 20, 135–146. Arnold, R., Bartl, A.-M., Hufnagl, E., 1993. Production of cord and narrow fabric products with Kemafil technology. Band- Flechtind. 1, 4–10. Arnold, R., Bartl, A.-M., Hufnagl, E., 1995. Recycling approach using the Kemafil technology. Tech. Text. 39 (1), 24–28. Baasch, A., Kirmer, A., Tischew, S., 2012. Nine years of vegetation development in a postmining site: effects of spontaneous and assisted site recovery. J. Appl. Ecol. 49, 251–260. Baxter, R., 2008. Wattles and other sediment control devices. Eros. Control 15, 44–51. Berthold, M., Arnold, R., 1975. Patent DD 110 905. Borgegård, S., 1990. Vegetation development in abandoned gravel pits: effects of surrounding vegetation, substrate and regionality. J. Veg. Sci. 1, 675–682. Bradshaw, A., 1997. Restoration of mined lands—using natural processes. Ecol. Eng. 8, 255–269. Bradshaw, A., 2000. The use of natural processes in reclamation - advantages and difficulties. Landsc. Urban Plan. 51, 89–100. Bradshaw, A.D., Chadwick, M.J., 1980. The Restoration of Land: the Ecology and Reclamation of Derelict and Degraded Land. Blackwell Scientific Publications, Oxford. Broda, J., Gawlowski, A., Rom, M., Laszczak, R., Mitka, A., Przybyło, S., GrzybowskaPietras, J., 2016. Innovative geotextiles for reinforcement of roadside ditch. Tekstilec 59, 115–120. Broda, J., Gawlowski, A., Laszczak, R., Mitka, A., Przybylo, S., Grzybowska-Pietras, J., Rom, M., 2017. Application of innovative meandrically arranged geotextiles for the protection of drainage ditches in the clay ground. Geotext. Geomembranes 45, 45–53. Broda, J., Gawlowski, A., Przybylo, S., Binias, D., Rom, M., Grzybowska-Pietras, J., Laszczak, R., 2018. Innovative wool geotextiles designed for erosion protection. J. Ind. Text. 48 (3) 599–61. Carroll, R.G., Rodencal, J., Collin, J.G., 1992. Geosynthetics in erosion control — the principles. Geotext. Geomembranes 11 (4–6), 523–534. Etra, J., 2011. Fiber roles or sediment logs: the rest of the story. Environ. Conn. 5, 20–21. García, C.B., Monical, J., Bhattarai, R., Kalita, P.K., 2015. Field evaluation of sediment retention devices under concentrated flow conditions. J. Soils Sediments 15,
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