The hydro-mechanical characteristics and micro-structure of loess enhanced by microbially induced carbonate precipitation

Microbially induced calcite precipitation (MICP) is an emerging biological method for soil improvement which has been applied to several soil types. However, only very limited research is conducted on the effectiveness of MICP treatment on loess, especially its hydro-mechanical characteristics. A set of unconfined compression, disintegration and scanning electron microscopy tests under various conditions were performed to quantify the mechanical and water stability of MICP solidified loess, including the cement reagent concentration (CRC = 0.5, 0.75, 1.0, 1.5 M) and curing age (CA = 0, 7, 14, and 28 days). Results indicate that MICP is a promising method for improving the mechanical property and water stability of loess under the present scenario of sustainable development worldwide. The uniaxial compressive strength (UCS) of MICP treated loess under CRC of 1.0 M curing for 14 days can be increased by 260%. The observed maximum performance of disintegration ratio of MICP treated loess is reduced by 68% through the self-designed disintegration instrument. Considering different CRCs, the empirical equation of UCS and deformation modulus of MICP-treated loess is proposed by regression analysis. In addition, with the aid of the scanning electron microscope, it is found that: (i) the precipitated CaCO3 crystals bridge and bind the loess particles together which can effectively increase the shearing resistance of loess skeletons; (ii) the CaCO3 aggregates filling in the pores between the loess particles could prevent the water molecules from damaging the original loess structures, and effectively reduce the disintegration of loess.