Application of microbial induced carbonate precipitation for loess surface erosion control

Abstract

China is one of the countries with the most serious soil erosion disaster, especially in Loess Plateau region. A new strategy for loess surface erosion control using MICP technology in terms of spraying was proposed. The feasibility, mitigation mechanism and the effects of MICP treatment cycle and cementation solution (CS) concentration were investigated through the rainfall erosion test and penetration test. It is found that the proposed MICP technique shows the ability to mitigate the rainfall erosion of loess. Final accumulative soil erosion weight could reach a maximum reduction of 200 times after only 3 cycles of MICP spaying treatment and almost no soil loss was observed since 5 cycles of treatment. The mitigation mechanism can be attributed to the MICP induced double layer structure, namely the upper hard crust layer on soil surface and the lower weak cemented layer, which is attributed to the bonding effect of the precipitated calcium carbonate (CaCO3) between soil particles and the filling effect in pores. The high structure strength of the hard crust can resist the impact of raindrops as well as can resist runoff erosion. The low permeability of the hard crust effectively prevents the rainwater infiltration to soft the subsurface weak cemented layer and deep uncemented soil. With increasing MICP treatment cycles, the amount CaCO3 and the thickness of the hard crust layer increases accordingly, leading to higher soil structure strength and erosion resistance. The CaCO3 content generally decreases with increasing depth. It is also found that the loess treated by 1.0 M CS presents the highest CaCO3 content, hard crust layer thickness and soil structure strength as compare with the samples treated by 1.5 M and 0.5 M CS. Taking into account the overall effectiveness, efficiency and cost, 5 cycles of MICP treatment with 1.0 M CS is optimal for the mitigation of the rainfall erosion of the tested loess.