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Hydrological properties of biochar-amended expansive soil under dynamic water environment and biochar-amended soil’s application in green roofs

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Li M. , Garg A. , Huang S. , Jiang M. , Mei G. , Liu J. , Wang H.

Acta Geophysica

2024

tom Vol. 72, no. 2

1055--1065

Biochar is widely used as a soil amendment in green roofs because it can increase the soil’s water-holding capacity, inhibit cracking, and provide nutrients for vegetation. The interaction mechanism between biochar and expansive soil is a significant factor in the performance of green roofs. However, research mainly focused on the hydrological scale (i.e. runoff regulation and rainwater storage), and there is a lack of research on the hydrological properties (i.e. hysteresis of soil-water characteristic curves, changes in soil pore size and pore distribution, formation and development of cracks and swelling-shrinking characteristics) of biochar-amended expansive soils under dynamic water environment. This test was conducted out on soil columns with expansive soil and 5% (by mass) biochar-amended under 5 drying-wetting cycles. The results showed that within the range of water content suitable for plant growth (i.e. between the anaerobic point and wilting point), the hysteresis area of soil-water characteristic curves of the amended soil is smaller than the bare soil at each drying-wetting cycle. The addition of biochar changes the pore size distribution of the soil, reduces the pore size and swelling-shrinking characteristics of the expansive soil, and inhibits the development of cracks. Therefore, the addition of biochar significantly attenuates the hysteresis characteristics of the soil-water characteristic curves of expansive soils, which may improve the stability of the hydraulic performance of green roofs. The results contribute to the understanding of the physicochemical and water properties of biochar-amended expansive soil and provide theoretical support for the application of biochar to green roofs.

Stabilization of Expansive Soil Mixture Using Human Hair Fibre (Biopolymer)

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Idoui I. , Bekkouche S. R. , Benzaid R. , Berdi I.

Civil and Environmental Engineering Reports

2024

tom Vol. 34, no. 2

63--75

Expansive soils sensitivity to volumetric change is one of the well-known challenges in the field of geotechnical engineering. Various attempts have been made by researchers to solve this problem. Current research presents the effect of human hair fibers on the behavior of expensive soils. A reconstituted soil of 80% kaolin as raw material and 20% bentonite with different percentages of human hair (0%, 0.5%, 1%, 1.5% and 2%) was used. The microstructure of the formulations was characterized by studying the interactions between soil and human hair using scanning electron microscopy (SEM). The microstructure of the formulations was characterized by studying the interactions between soil and human hair using scanning electron microscopy (SEM). Atterberg limits, compaction characteristics, swelling parameters, compressibility and shear strength were also examined. The results of this study indicate that the inclusion of human hair fibers significantly improves the properties of the expansive soil mixture. These results open up new prospects for the stabilization of expansive soils.

Mechanism of compacted biochar amended expansive clay subjected to drying–wetting cycles: simultaneous investigation of hydraulic and mechanical properties

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Wang H. , Garg A. , Huang S. , Mei G.

Acta Geophysica

2020

tom Vol. 68, no. 3

737--749

Biochar has been extensively studied in the aspect of amendment of compacted sandy/clayed soils, whereas its application as amendment in expansive soil is rare. Hydraulic and mechanical properties of biochar-amended expansive soil especially impacts of drying–wetting cycles have been rarely investigated. Aiming at construction of sponge city, straw biochar-amended expansive soil and the control soil (i.e., without biochar) are subjected to drying–wetting cycles in this study. During drying–wetting cycles, energy-dispersive spectrometer and Fourier transform infrared (FTIR) spectroscopy analyses were conducted to investigate microchemical composition including. Pore size distribution and microstructure were measured using nitrogen gas-adsorption technique and scanning electron microscope, respectively. Further, changes in soil water retention curve, void ratio, crack intensity factor (CIF, i.e., ratio of cracked section area to the total soil area) and shear strength were also determined. It is found that there is no diference in water retention capacity between various soils for near-saturated samples. Under high suction, however, more water could be retained within mesopores of biochar-amended soil. FTIR analysis indicates that biochar-amended expansive soil shows stronger chemical bonding, irrespective of them being subjected to drying–wetting cycles. The weak alkalinity of straw biochar results from its main chemical composition (i.e., calcium carbonate). It is noteworthy that straw biochar improves soil water retention capacity, which further restrains desiccation cracks. Cohesion of biochar–soil composite is also improved due to chemical bonding. Aiming at green roofs, straw biochar could be promising option for expansive soil amendment technically and economically.