Application of Bio-Stimulated Calcite Precipitation to Stabilize Expansive Soils: Field Trials

This paper presents the results of a field implementation of microbial induced calcite precipitation to stabilize expansive soils in Marsing, Idaho. The field test was done by drilling 2.5" (6.35 cm) diameter holes at a spacing of 16" to 30" (40.6 cm to 76.2 cm) into the ground and, injecting bio-enrichment followed by bio-cementation solutions to stimulate the native bacteria and subsequently achieve calcite precipitation. The pH level of the soil, the calcite content, and free swelling potential were monitored over time by collecting periodic soil samples from the injection points. An increase in pH from 8.3 to 9.7 was seen in the first seven days after the injection of bio-enrichment solution. The calcite content in the soil increased and the free swelling potential decreased consistently with each subsequent injection of bio-cementation solution. The calcite content increased from 3% to 8% and the free swell index dropped from 114% to 29%. The results show that microbial induced calcite precipitation can be successfully replicated in the field for the stabilization of expansive soils.