Shear Strength and Wind Erosion Potential of Biologically Improved Sand

Abstract

In the current study, Microbial-Induced Carbonate Precipitation (MICP) is used for the improvement of silty sand to mitigate wind erosion by spray-treating the soil surface layer with bacterial cell solutions. Wind tunnel, soil pocket penetrometer, and Torvane shear tests were carried out on the biologically treated and untreated samples. The bacteria were sprayed at bacterial concentrations of 0.05, 0.1, and 0.5 g/m2 and the samples were exposed to wind speeds of 20.57, 26.18, and 31.79 m/s. The results showed that the effect of wind speed was more pronounced in the untreated samples than the treated samples. A marked decrease in wind erosion potential was observed in the treated samples which was dependent on the bacterial concentration. An increase in the bacterial concentration from 0.05 to 0.5 g/m2 and in the curing time from 2 to 28 days decreased the wind erosion of the treated samples. Pocket penetrometer values were primarily affected by curing time and were almost independent of the bacterial concentration. The pocket penetrometer values of the treated samples were generally less than 2 MPa, which indicates the possibility of root growth. The results of the Torvane shear tests indicate that bio-cementation through MICP also increased the shear strength development of loose sand deposits. Scanning electron microscopy images of the structure of the treated samples revealed that MICP bound the sand particles together through CaCO3 crystal formation in the voids between the particles.