Mechanical behavior and damage failure of biochar-modified solidified dredged sediment

Biochar, a porous environmental functional material derived from pyrolysis of the biomass under anaerobic or low-oxygen conditions, has demonstrated unique advantages in solid waste recycling and the remediation of river and lake sediments. This study explores the solidification/stabilization of dredged sediments using alkali-activated composite cementitious materials combined with sludge biochar (SB). A comprehensive experimental program, comprising orthogonal design, compaction tests, Atterberg limit tests, and unconsolidated undrained (UU) triaxial shear tests, was conducted to analyze the physicomechanical properties, strength, and failure of the solidified bodies. A statistical damage constitutive model accounting for multifactorial influences was developed. The results indicate that the internal friction angle is most sensitive to compaction degree, while cohesion is primarily influenced by the strength of the solidifying agent. Both the strength and dosage of the solidifying agent, compaction degree, and biochar content exert positive effects on the internal friction angle, whereas water content has a negative impact. Overall, cohesion increases with higher dosages of the solidifying agent. The proposed damage constitutive model was calibrated using the particle swarm optimization (PSO) algorithm and showed good agreement with experimental results. Mechanically, strain hardening behavior was observed at low levels of solidifying agent and confining pressure, while strain softening occurred under higher levels of both. Failure mode analysis revealed that increased material strength coupled with low confining pressure led to more brittle behavior, characterized by energy release, multiple failure planes, and larger shear angles. The incorporation of biochar effectively alleviated this brittleness. This study provides a systematic investigation into the influence of key process parameters and the mechanical behavior of solidified dredged sediment (DS), offering essential reference parameters and a theoretical foundation for practical engineering applications.