Microbial strengthening of loose sand

Aims: To test whether the addition of Flavobacterium johnsoniae could increase the strength of saturated Ottawa 30 sand. Methods and Results: A box model was built that simulates groundwater-like flow through a main sand compartment. Strength tests were performed at seven locations and at two depths, 10 center dot 8 and 20 center dot 3 cm below the top of the tank, using a vane shear device before and after the addition of bacteria. After the addition of Fl. johnsoniae, sand samples were obtained from multiple sampling ports on the vertical sides of the box model. The presence of a bacterial biofilm was confirmed by staining these sand samples with SYTO-9 and Alexa Fluor 633 and viewing with a confocal microscope. The average shear strength increases after the addition of Fl. johnsoniae were 15 center dot 2-87 center dot 5%, depending on the experimental conditions. Conclusions: Flavobacterium johnsoniae caused a statistically significant increase in the strength of saturated Ottawa 30 sand. Significance and Impact of the Study: Biofilm-forming bacteria can increase the shear strength of saturated sand. The addition of biofilm-forming bacteria to a building site may be an alternate method to mitigate the effects of liquefaction.