Enzyme-induced carbonate precipitation (EICP) combined with lignin to solidify silt in the Yellow River flood area

• A novel EICP-lignin treatment for soil was proposed for the modification of silt in the Yellow River flood area. • The optimum lignin content was approximately 5% for the EICP-lignin treatment of soil. • The relationships between the strength parameters and the lignin level in the treatment were investigated. A novel method that combines enzyme-induced carbonate precipitation (EICP) and lignin was proposed to improve the mechanical properties of silt in the Yellow River flood area. The silt in this area is characterized by poor particle gradation, weak cohesion and low strength. It is essential to focus on the modification of silt by environmentally friendly methods. The work described in this paper investigated the unconfined compressive strength (UCS), elastic modulus, cohesion, internal friction angle and microstructure of EICP-lignin treated silt. A series of laboratory experiments was conducted, including the unconfined compressive strength (UCS) test and consolidated undrained (CU) triaxial test. The results proved that the EICP-lignin treatment enhanced silt obtained from the Yellow River flood area. All the strength parameters increased and then decreased with increasing lignin content, and their values were optimum for approximately 5% lignin. Specifically, the optimum UCS strength, cohesion and internal friction angle improved to approximately 5, 10, and 3 times those of untreated silt. In addition, the strength parameters gradually increased with curing time. Microstructure analyses were used to illustrate the physical basis for the improvement in strength with increasing aggregation of lignin and calcite.