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The use of natural materials in place of synthetic materials has been the focus of research in sustainable geotechnics. In this context, use of natural plants/weeds as randomly distributed fiber-reinforced soil (RDFS) is extensively researched as a possible soil-improvement technique. The behavior of soil–natural fiber composite is dependent on the biochemical, physical, and mechanical properties of natural fibers. These natural-fiber properties are inherently different from those of conventional synthetic fibers, in which mechanical properties essentially govern the soil-fiber composite behavior. Very few geotechnical applications using natural geo-reinforcement materials have taken into consideration the biochemical and physical properties of the fiber. Moreover, there is rarely any systematic assessment and compilation of the work encompassing the application of natural fibers in soil reinforcement. This review summarizes the use of natural fibers in soil reinforcement. The study explores the importance and impact of natural-fiber properties on the performance of natural fibers in subsoil conditions. The treatment methodologies used in natural fibers to increase their longevity and reinforcement capabilities are also discussed. Based on this review, some key research gaps and the future scope of research have been highlighted. The review strongly recommends potential natural flora as RDFS fibers from a sustainability perspective. The review brings out the importance of biochemical composition (cellulose, lignin, hemicellulose, etc.) on fiber performance in subsoil conditions and highlights the use of treatment methodologies for fibers.

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Biochar (BC) has been proposed as an alternative soil amendment in landfill cover. Its effects on soil hydraulic properties (e.g. soil water retention) have been explored to some extent, while its influence on landfill gas flow characteristics is not clear yet. The objective of this study is to investigate the water retention and gas permeability (kg) of BC-amended soil and its relationship with soil water content in unsaturated state. In total, three BC contents (0, 5 and 10%) were considered in clay–sand mixtures. Soil suction, water content and gas pressure were measured continuously using a new in-house developed apparatus. Test results show that the presence of BC increased soil water content and the increased amount was almost the same over a wide range of suction values (up to 3 MPa). kg increased linearly with soil suction in semi-log scale, regardless of the BC content. The addition of 5 and 10% of BC could decrease kg by up to 50 and 65%, respectively, compared with that of the bare soil. kg decreased with water content for both soil and BC -amended soils. Moreover, the decrease rate of kg with water content became smaller when the BC percentage was higher.

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