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In geo-environmental applications, the potential of biochar has been explored as a suitable cover material of landfill and vegetated slopes. The inherent nature of biochar affects the geo-environmental properties of the soil-biochar composite like water retention, compressive strength, infiltration, and soil erosion. Performance of a cover depends on biochar's surface functional groups, which can be either hydrophobic or hydrophilic based on bio-source. The objective of this paper is to investigate the geotechnical properties of biochar-amended soil sourced from two contrasting feedstock, i.e., poultry litter (animal based) and water hyacinth (plant based). The test results show that biochar addition increased the Atterberg limits and reduced the acidity of soil. Biochar addition directly increased the optimum moisture content and decreased the maximum dry density. Both biochar addition decreased the composite compressive strength by 25–50% but increased the ductility of composite. Water hyacinth biochar (WHB) inclusion decreased the erosion rate of soil while it is not the same for poultry litter biochar (PLB). In the case of water retention, only the addition of WHB increases retention and holding capacity of soil. The obtained results have been discussed in context with the conducted microstructural, chemical, and physical tests on both biochar. Through these analyses on biochar of different origin and having contrasting functional groups and intra-pore network, the development of a complex biochar-water network was confirmed. [ABSTRACT FROM AUTHOR]

Biochar is a recalcitrant material obtained after pyrolysis of labile biomass under oxygen-limited condition. The conversion of biomass into biochar is considered to be a sustainable way of generating bioenergy, minimizing the emission of greenhouse gases and managing the waste. Recently, the amendment of biochar in soil gained attention due to its multiple soil ameliorating features. Many studies have investigated the effect of biochar particle size on the physicochemical and hydraulic properties of relatively loose agricultural soil. However, such study is rarely conducted for compacted soil suitable for bioengineered structures. The objective of the current study is to investigate the effect of biochar particle size on the hydraulic conductivity of compacted soil for bioengineered structures. Saturated hydraulic conductivity (Ksat) of different compacted soils amended with biochar of different particle sizes ranging from 0.075 to 4.75 mm has been investigated. The results showed that the amendment of 5% to 15% (w/w) biochar of different particle sizes led to the change in Ksat of the silty sand. When compared with bare soil, a higher Ksat with biochar of particle size larger than 0.425 mm and a lower Ksat with particles of size smaller than 0.425 mm was observed. However, in pure sand, a lower Ksat irrespective of particle size of biochar was observed and the lowest Ksat was noted with biochar of particle size smaller than 150 mm. These changes in the Ksat after biochar amendment were attributed to the alteration of pore structure mainly, inter-pores of the soil, which is controlled by the particle size of the biochar. The findings of the present study could be useful for the field application i.e. in bioengineered structures. [ABSTRACT FROM AUTHOR]

Bioengineered structures, such as landfill cover, vegetated slopes or embankments, green roof and turf are comprised of soil and vegetation where vegetation imparts stability and protection through root reinforcement and hydrologic action. Soil in bioengineered structures often compacted and subjected to prolong drying due to irregular irrigation which necessitates the investigation of soil properties and vegetation growth in biochar-amended soil (BAS) under large suction range and it is scarce in the literature. In the present study, the effect of different biochar types on soil properties, and the vegetation growth in compacted soil and under large suction range was investigated for application in bioengineered structures. The results revealed that the biochar amendment decreased the dry density (5–32%) and increased the water retention capacity (θs by 15–104%, θ1500 by 82–445% and plant available water content (PAWC) by 22–55%), pH (28–77%) and cation exchange capacity (CEC, 16–723%) of the soil. Further, the vegetation growth i.e., vegetation density, dry root mass and shoot mass increased by 8–13%, 33–108% and 4–157% respectively after biochar amendment. The vegetation wilting was started at a higher suction (~ 900 kPa) relative to bare soil (800 kPa), the permanent wilting point (PWP) increased (by 3–35%) and the complete photosynthetic activity remained unchanged at a higher suction (1600 kPa) relative to bare soil (1050 kPa) after biochar amendment. Among the biochar types i.e., Sugarcane Bagasse biochar (SBB), Mesquite biochar (MB) and Water Hyacinth biochar (WHB) tested, the MB showed the best performance i.e., the suitable vegetation growth and health status. The improved water retention due to increased porosity, specific surface area (SSA) and presence of hydrophilic functional groups, and the higher pH, CEC and lower dry density in BAS attributed to the higher vegetation growth. The findings of the present study suggest the application of BAS in bioengineered structures. [ABSTRACT FROM AUTHOR]

Biochar is a carbon-rich and low microbial degrading material obtained after pyrolysis of biomass in the absence or limited content of oxygen. The impact of biochar on hydraulic properties of soil is extensively studied in agricultural and geotechnical or geoenvironmental engineering for potential application in bioengineered structures. While a little study is conducted to assess its effect on soil mechanical properties, especially shear strength. However, the effect of biochar on the combined shear strength and compaction characteristics of soil is not studied. The shear strength of biochar amended soil is thought to be related to the compaction characteristics. In addition, the effect of biochar on the shear strength of the soil is soil and biochar specific. In this study, an attempt was made to investigate and better understand the effect of biochar on the shear strength and compaction characteristics of a clayey sand for potential application in bioengineered structures. Standard proctor, direct shear and unconfined compression tests were conducted on bare soil and soil amended with 5, 10 and 15% (w/w) biochar. The experimental results revealed that the amendment of biochar from 5 to 15% (w/w) decreased the dry density and increased the shear strength parameters such as cohesion (c) and angle of internal friction (ϕ) of the soil. While it decreased the undrained shear strength (cu) at higher compaction density (> 0.95MDD) and increased at lower compaction density (< 0.9MDD). Thus, in undrained condition, the initial compaction density has a strong influence on the shear strength of biochar amended soil. In addition, the increased c and ϕ and decreased dry density in biochar amended soil is observed to increase the stability of slopes (hypothetical). The increase of c and ϕ is believed to be due to the roughness and active chemicals (functional groups) present on the surface of the biochar. The decreased cu at higher density is believed to be due to the lubricating effect by the higher water content. [ABSTRACT FROM AUTHOR]

Biochar is a carbon-rich material produced mainly from plant- and animal-based biomass through thermochemical conversion. It is often amended to soil for methane oxidation in landfill cover soil and for improving crop growth and yield by enhancing soil fertility. The application of biochar for removing organic and inorganic pollutants from soil and water is also well established. Biochar could be of potential use as an engineering material for enhancing the stability and performance of bioengineered structures that mainly consist of soil and vegetation. Bioengineered structures are commonly adopted in many parts of the world due to their multiple beneficial features. The stability and performance of these structures depend on the soil engineering properties and vegetation performance. However, the performance of vegetation is interrelated with the soil engineering properties. Therefore, the effects of biochar on soil engineering properties and vegetation performance, i.e., the soil-biochar-plant interaction, need to be studied and summarized. In the present study, the effect of biochar on the soil engineering properties and vegetation performance was reviewed. The review of the literature revealed that the amendment of biochar affects the soil engineering properties and vegetation performance by altering mainly soil pore system and fertility. However, this depends on many factors, such as soil type, biochar type, pyrolysis temperature, particle size of biochar, biochar amendment rate, aging of biochar, and the type of vegetation grown. Furthermore, the reviewed or existing literatures are mostly for agricultural soil, which is different from the soil state in bioengineered structures in terms of compaction density, suction range, and design life or duration. In addition, the properties of biochar are highly variable with its production process. Hence, the factors of soil state in bioengineered structures and the optimized production process of biochar need to be considered for maximizing the long-term performance of bioengineered structures. [ABSTRACT FROM AUTHOR]