Conclusions

Bio-cementation tests were conducted to investigate the effects of the combined MICP-PVAc technology on the improvement of loess-slope surface erosion resistance. Moreover, PVAc was added to the cementation solution, which further improved slope stability. The results demonstrated that MICP-PVAc treatment significantly mitigated surface erosion of loess-slope. Specific conclusions are outlined as follows:
(1) MICP treatment resulted in an improvement of erosion resistance and treatment with 6 L/m2 of mixed solution achieved the best erosion control and the highest surface strength. The soil loss in MICP treated slopes, however, still remained large. Therefore, a better treatment was necessary to effectively and efficiently control the erosion of loess-slope surfaces.
(2) Addition of PVAc had little impact on urease activity and production rates for calcium carbonate. After treatment with MICP and PVAc together, the stability of loess-slope improved significantly. For slopes treated with the addition of PVAc at 40 g/L or 60 g/L, 50 min of exposure to rainfall caused little soil loss because of the better cementing effect.
(3) With the addition of PVAc to the cementation solution, the surface strength of slopes increased beyond that of slopes treated with MICP only. With 60 g/L PVAc, the surface strength of slope P5 decreased below that of slope P4, but still remained higher than that of slope P3 because of the lower thickness of cementation.
(4) The high erosion resistance of P4 and P5 was attributed to (1) the stable spatial structure of CaCO3 precipitation, and (2) the stronger resistance to tension or shear force from PVAc. The method proposed in this study provides an effective and efficient t