This project explored the use of Microbial Induced Calcite Precipitation (MICP) via biostimulation to stabilize problematic expansive soils. Expansive soils cause billions of dollars of damage annually due to their ability to undergo significant volume changes with water content fluctuations. Various ground improvement techniques like chemical stabilization, deep soil mixing and moisture barriers are employed to counteract the problems caused by these soils; however, these methods are either expensive or impact the environment negatively. A more sustainable and economic alternative is the microbiological treatment of soils. Microbial Induced Calcite Precipitation (MICP) is an innovative process that could be used to improve the engineering properties of soil through calcite precipitation using urease-producing bacteria. The project tasks were accomplished in two stages: stage 1 involved laboratory experiments while stage 2 focused on preliminary fieldwork. The objectives of the laboratory work were to study the role of soil type, clay content and bacterial populations on treatment effectiveness and develop a protocol for field implementation. Preliminary field work was performed to evaluate the laboratory protocols in the field.
Overall, it was found from laboratory tests that, there was increased calcite precipitation with increasing clay content in natural soils. The impact of calcite precipitation on strength improvement and swell reduction was significant. The laboratory results showed clearly that it was possible to achieve calcite precipitation in natural soils using native soil bacteria and alter the behavior of the soils. Field test results showed that calcite precipitation increased with treatments (up to 8% total) and the free swell index dropped from 114% to 29%. It was concluded that MICP can be successfully replicated in the field through successive injections of enrichment and cementation solutions into the soil. Based on the preliminary field tests, a field protocol has been developed for future field implementations. Additional field tests are necessary for improving the system and realizing the full benefits of the MICP.
The final report is available.