Assessment of Microbial Induced Calcite Precipitation (MICP) in Fine Sand Using Native Microbes under Both Aerobic and Anaerobic Conditions

Abstract

Microbial induced calcite precipitation (MICP) technology in recent decade has been introduced to geotechnical engineering society as a mean for soil improvement. In this regard stimulation of indigenous aerobic and anaerobic bacteria is an alternative to bioaugmentation process in which bacteria are added to the soil. The aim of this study was to compare the effects of the bio cementation process on natural sand samples by stimulation of indigenous anaerobic and aerobic bacteria. About 109 natural intact samples of poorly graded sand samples were collected from the field in polyvinyl chloride (PVC) tubes 10 cm in diameter and 50–100 cm in height. They were then treated with different stimulating solutions by injection procedure. After 7, 15, and 21 days of treatment, direct shear (DS), unconfined compressive strength (UCS) test results, calcite content, and scanning electron microscopy (SEM) images obtained using an instrument equipped with an energy dispersive X-ray spectroscope (EDX) were used to analyze the samples. Results demonstrated that the values of UCS for the samples through stimulation of aerobic bacteria were 22–73% higher than those for the samples treated through stimulation of anaerobic bacteria. Samples treated for stimulation of both aerobic and anaerobic bacteria produced 8–15% calcite whereas samples treated for stimulation of either aerobic or anaerobic bacteria alone produced only1–6% calcite. The values of UCS for samples treated for stimulation of both aerobic and anaerobic bacteria were increased by 254–283% and those for samples treated for stimulation of either aerobic or anaerobic bacteria alone increased by 156–270% from that for the untreated samples.