| description abstract | The repeated expansion–contraction deformation significantly decreased the strength of expansive soils. The undesirable properties of expansive soils posed a safety threat to engineering construction. Biochar and bagasse fibers satisfied the requirements of expansive soil improvement as green materials. This study used biochar and bagasse fibers to improve expansive soils. The expansive soil was obtained from Chongzuo in Guangxi, China. The biochar was added to the soil at six contents of 0%, 2%, 4%, 6%, 8%, and 10% by weight. The bagasse fiber was added to the soil at five contents of 0%, 0.1%, 0.2%, 0.3%, and 0.4% by weight. Extensive tests were conducted on the expansion–contraction characteristics, water-retention, mechanical strength, and particle size distribution of original expansive soil, biochar-improved soil (BIS), and biochar-bagasse fiber composite-improved soil (CIS). The improvement effect of biochar and bagasse fiber on expansive soils was discussed. Scanning electron microscopy imaging was carried out to reveal the microscale mechanism of expansive soil improved by biochar and bagasse fibers under drying–wetting cycles. The results indicated that the expansion potential and plasticity index decreased by 56.5% and 34.1% as the biochar content increased from 0% to 10%. Meanwhile, the water-retention capacity has been improved. The agglomeration of biochar and the reinforcing–restraining effects of bagasse fibers significantly improved the linear shrinkage, shear strength index, and unconfined compressive strength (UCS). When the biochar content was 8% and bagasse fiber content was 0.3%, the linear shrinkage decreased from 11.1% to 3.2%, the cohesion increased by 78.1%, and the UCS increased by 64.3%. CIS exhibited high stability under drying–wetting cycles. Its strength loss was smaller than that of BIS. The study provides a new solution for expansive soil improvement in roadbed filling, slope protection, and other projects. Expansive soils are a commonly hazardous soil. Safe construction on sites underlain by expansive soils represents a significant challenge to geotechnical engineers. Traditional methods for improving such ground conditions include deep soil mixing, which involves the use of portland cement. Portland cement is effective in reducing the expansivity and improving the shear strength of problematic soils. However, it has a large carbon footprint as a building material due to its energy intensive manufacture and resulting CO2 emissions. Ecosystem sustainability would be hindered with the extensive utilization of such materials. Biochar and bagasse fiber are common biomass resources. More importantly, biochar utilization is a meaningful way to accelerate the achievement of carbon neutrality. Bagasse is one of the most productive agricultural solid wastes in the world. Bagasse fiber has excellent mechanical properties such as good toughness, high specific strength, and high specific stiffness. This study proposed a method using biochar and bagasse fibers to improve the undesirable properties of expansive soils, and good research results were obtained. It was found that biochar and bagasse fibers significantly improved the expansion–contraction behavior, water-retention, and strength of expansive soils. This improvement method simultaneously fulfilled the requirements for the effective treatment of expansive soils and reduced the pressure for waste disposal. | |
