Settlement Behavior of Bacterium-Embedded Soft Clay Sediment: Sedimentation and Low-Stress Consolidation Experiment

This study explores the effect of bacteria on the large-strain settlement behavior of kaolin sediment. It first performed a sedimentation test using a kaolin suspension mixed with a representative lake-sediment bacterium, Shewanella oneidensis MR-1. Subsequently, a consolidation test was conducted with the deposited kaolin sediment, gradually increasing the vertical effective stress to ∼80 kPa. The results show that the interaction between clay and bacteria results in fast sedimentation and dense sediment after sedimentation by promoting aggregated fabric. Such clay-bacteria aggregation induces a precompression effect on the kaolin sediment, leading to reduced compressibility, enhanced stiffness, and higher hydraulic conductivity compared to the abiotic sediment at the same void ratio during consolidation. The consolidation results indicate a threshold vertical effective stress of approximately 20 kPa, beyond which bacterial influence becomes negligible and settlement is primarily governed by the applied vertical stress. Nevertheless, the clay-bacteria interaction reemerges during the unloading-reloading stages by suppressing the deformation of consolidated kaolin sediment. This study advances the fundamental comprehension of settlement behavior in the early diagenesis of clay deposits under a bacterium-enriched environment and how particle-level clay-bacteria interactions affect the macro-scale behavior of the sediment.