Effect of wetting and drying on the mechanical properties of MICP treated clay

Abstract

Microbial-induced calcium carbonate (MICP) mineral precipitation is a fairly new and innovative technique in soil stabilization. MICP was originally applied to coarse grained soil with success. The use of MICP in the fine-grained soil is rare, so far. MICP process involves using bacterial strains that can secrete urease enzymes, called urease positive bacteria (UPB) and chemical which include urea and calcium carbonate. The bacterial strains used in this research are Bacillus subtilis and Priestia megaterium. An expansive soil obtained from Nandipur; Pakistan was used in the study. The unconfined compressive strength (UCS) and Atterberg limit tests were performed to examine the mechanical behaviour of MICP treated soil for different wet-dry cycles. Microstructural analysis, such as X-ray diffraction (XRD), and scanning electron microscopy (SEM) was conducted to observe the surface and internal structures. The result showed that the treated soil gave 4 times higher UCS than untreated soil, which is due to change in its composition. Furthermore, the MICP treated soil demonstrated insignificant decrease in strength after 7th wet-dry cycle. The results infer that that MICP is an efficient technique to stabilize the swelling soil.