Influence of Fiber Addition on Mechanical Properties of MICP-Treated Sand

Microbial-induced calcite precipitation (MICP) is one of the environmentally friendly ways to improve engineering properties of sandy soil. A laboratory study was conducted to investigate the effect of randomly distributed discrete fiber on the mechanical properties of MICP-treated soil and to discover the corresponding mechanisms. Specimens were prepared at four different fiber ratios (0.1, 0.2, 0.3, and 0.4% by weight of sand). MICP were catalyzed by Sporosarcina pasteurii at the concentration of $4.3\times {10}^7\mathrm{cells}/\mathrm{mL}$. MICP-treated sand samples were prepared using full-contact flexible molds. The results showed that remarkable improvements in shear strength, ductility, and failure strain were achieved with fiber addition in the MICP-treated sand. The unconfined compression strength (UCS) and shear strength increased gradually with an increase in fiber content up to a fiber content of 0.3%. The optimum fiber content in the MICP-treated sand was found to be 0.2–0.3%. The UCS of MICP-treated sand at the optimum fiber content is more than two times higher than that without addition of fiber. The failure strain of MICP-treated sand at the optimum fiber content is nearly three times higher than that without addition of fiber. Residual strengths of MICP-treated sand at the optimum fiber content are near 100 kPa, while the residual strength is 0 kPa for that of MICP-treated sand without fiber. The cohesion and angle of internal friction of fiber-reinforced sand prepared at different ratios of fiber increased by 29–45 kPa and 7.6–11°, respectively. The inclusion of fibers increases the residual strength occurring after peak stress and decreases the brittle behavior of the MICP-treated sand.