Unconfined compressive strength of bacillus Pumilus treated lateritic soil

Abstract

The study considered the use of Bacillus pumilus to trigger microbial-induced calcite precipitation (MICP) process for the improvement of the unconfined compressive strength (UCS) of lateritic soil to be used as a hydraulic barrier in waste containment application. The lateritic soil was treated with stepped Bacillus pumilus suspension densities of 0, 1.5 × 10 8 , 6.0 × 10 8 , 12 × 10 8 , 18 × 10 8 and 24 × 10 8 cells/ml, respectively. Specimens were prepared at moulding water contents –2, 0, 2 and 4% relative to the optimum moisture content (OMC) that simulate field variation in moisture and compacted with British Standard light (or standard Proctor) energy. The UCS values increased with higher Bacillus pumilus suspension densities and moulding water content. Peak UCS values of 1159.08, 1169.52, 1298.27 and 1884.58 kN/m 2 were obtained at 6.0 × 10 8 /ml, 24.0 × 10 8 /ml, 6.0 × 10 8 /ml and 18 × 10 8 /ml Bacillus pumilus suspension densities for specimens prepared at –2%, 0%, +2% and +4% relative to OMC, respectively. A compaction plane of acceptable zones for UCS based on regulatory value (i.e., > 200 kN/m 2 ) gave 6.0 × 10 8 /ml Bacillus pumilus suspension density as optimum treatment for lateritic soil to be used in waste containment application.