Field experimentation of bio-cementation using low-cost cementation media for preservation of slope surface

Microbial induced carbonate precipitation (MICP) is a promising bio-cementation method that involves ureolytic bacteria to improve the geotechnical properties of soil. The laboratory-scale studies carried out in the recent past showed that the MICP can be a potential alternative for slope surface preservation. However, the use of analytical-grade chemicals makes this method too expensive, limiting the applicability of the method especially when implicated at field-scale. The purpose of this research work was to assess the effectiveness of using inexpensive low-grade chemicals for the in-situ stabilization of slope surface. Two test plots were established at the project site (Hokkaido expressway slope, Japan) and subjected to MICP treatment via surficial spraying. One was treated using the cementation media formulated by low-grade chemicals (inclusive of fertilizer urea, snow-melting agent and beer-yeast), while the typical analytical-grade media was used to treat the other plot. After 20 days of treatment, the treated slope surfaces were evaluated by surface strength, CaCO3 content, scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. The outcomes indicated that the surface was significantly improved by low-grade chemicals; a stiff surface layer was desirably formed to the depth of 5 – 10 cm with the surface strength and CaCO3 content in the ranges of 0.14 – 1.02 MPa and 0.56 – 3.7%, respectively. The results are compared and discussed, and the challenges in the use of low-grade chemicals are pointed out for the way forward. Cost analysis disclosed that the material cost of the cementation media was reduced by around thirty-seven-fold (by 97%) compared to the analytical-grade media. While demonstrating the potential use of low-grade chemicals, the field-scale experiment could contribute to narrow down the gap between the present-state and real-scale deployment of MICP technology.