Effects of biochar on the compressibility of soil with high water content

Abstract

This study investigates the potential utilization of biochar in reclamation fills to improve the compressibility of soil with high water content. Biochar, a recycled carbon-rich biomass commonly used for contaminated soil remediation and carbon sequestration, is examined for its impact on the compression behavior of treated soils. The influence of biochar content, initial water content (w0), and biochar saturation on the compression behavior of biochar-treated soils with high water content is analyzed. The results revealed that the addition of both raw biochar and biochar saturated with water significantly enhances the remolded yield stress (σ′yr) and reduced the void ratio (eyr) at σ′yr. Raw biochar exhibits higher σ′yr and lower eyr values compared to water-saturated biochar, mainly due to its greater water absorbing potential of raw biochar. The variations of σ′yr and eyr induced by biochar can be attributed to the decrease in initial void ratio (e0) and the increase in void ratio at liquid limit (eL), which can be effectively normalized using empirical equation developed for reconstituted soil without biochar. Furthermore, the compression parameters (e*100 and C*c) show a decreasing trend with increasing biochar content and decreasing initial water content. Soil with saturated biochar displays higher e*100 and C*c values in comparison with soil with raw biochar. The changes in e*100 and C*c corresponded well to empirical equations developed for reconstituted soil without biochar, indicating that the compressibility changes induced by biochar depended on variations in physical properties (e0 and eL), following similar patterns observed in reconstituted soils without biochar. Therefore, the compression curve of biochar-treated soil in the postyield regime can be effectively normalized by using void index into the ICL or EICL, suggesting its practical applicability for predicting the compressibility of reclamation soil with biochar. These findings demonstrate that biochar-treated soil with high water content exhibits favorable geotechnical properties, making it suitable for use as soil reclamation fills or in landfill applications.