Engineered use of microbial gas production to decrease primary consolidation settlement in clayey soils

This feasibility study examines the use of in situ microbial gas production to engineer the consolidation properties of clayey soils by changing the settlement–time profile. A simple analytical model has been proposed to assess the swelling of the soil during the steady-state gas production, and to predict immediate settlements due to loading at the end of this process. For experimental validation of the suggested technique, Clostridium acetobutylicum, an anaerobic fermentative microorganism, was mixed into clayey-sand samples, fed with a nutrient-rich medium, and allowed to produce gas in situ. A series of standard oedometer tests was performed on gas-containing and gas-free soil specimens. Results showed that, in agreement with the model predictions, in situ gas production caused negligible swelling of the samples, while shifting a significant portion (up to 50%) of total displacement from primary consolidation settlement to immediate settlement without changing total displacements or the coefficient of consolidation.