Exploring the application of the MICP technique for the suppression of erosion in granite residual soil in Shantou using a rainfall erosion simulator

Granite residual soil is vulnerable to collapse under rainfall-induced erosion. This may in turn lead to the occurrence of landslides or debris flows on slopes. Previous studies on use of microbial-induced carbonate precipitation (MICP) technique for soil stabilization are often conducted on sandy soils and also with rainfall-induced erosion are rarely assessed for a slope treated with MICP. This study investigated the feasibility of using the MICP technique for surface protection of granite residual soil slopes against erosion. The MICP technique was applied to soil samples using the spraying method. Hydraulic conductivity and rainfall erosion tests (using flume) were conducted to assess the coating effects of MICP on granite residual soils. In addition, crust thickness, calcite content and near-surface strength were measured to interpret the results. Tests were repeated to assess any variability in results. Scanning electron microscopy, energy-dispersive spectrometer and X-ray diffraction (XRD) were conducted on treated and untreated samples to interpret the formation of calcite due to MICP. After 7 days of curing, the calcite content increases to 4.3%, whereas mean coating thickness is 4.2 mm. Unconfined compressive strength is increased by 20.3% as compared with the bare soil. MICP treatment reduced the soil hydraulic conductivity and erosion rate by 90.9% and 95.2%, respectively. This was attributed to the bio-cementation process generating a surface coating on granite residual soils, leading to a reduction in pore throats, as observed in the obtained micrographs. Compared to the bare soil, the runoff rate in the MICP-treated soil was increased by 39.4% on average. However, the erosion is found to reduce significantly in MICP-treated soil. Based on ANOVA analysis, it could be concluded that the rainfall intensity found to be a significant factor affecting the erosion rate of granite residual soil slopes.