Coupling effect of biocementation-fiber reinforcement on mechanical behavior of calcareous sand for ocean engineering

Microbial induced calcium carbonate precipitation (MICP)-based biocementation method coupled with fiber reinforcement was adopted to improve the engineering properties of calcareous sand. Apart from increasing the strength properties such as the unconfined compressive (UC) strength and residual strength, the added polypropylene fibers also yield great ductility and toughness of MICP fiber-reinforced calcareous sand. In general, the higher the fiber content, the larger the UC strength and residual strength, and the better the ductility and toughness. Compared to just MICP improved samples, the increments of the UC strength, ductility, toughness were up to 2.6, 3.5, and 5.0 times of magnitude, respectively, when the fiber content was 0.4%, whereas the corresponding residual strength was 63.1% of the UC strength. According to the observed microstructure results from X-ray CT and SEM tests, the fiber reinforcement on the mechanical behavior of MICP improved calcareous sand can be attributed to the effective bonding promotion, fiber interlacing effect, and extra anti-pulling force providing. The coupling effect of the effective bonding promotion and fiber interlacing enhanced the bearing capacity of the treated calcareous sand samples when subjected to small stress with small deformation. When the deformation increased, anti-pulling forces provided by the restraining fibers contributed much more to the bearing capacity and dramatically improved the ductility and toughness. Moreover, the addition of fibers delayed the occurrence of the unstable crack growth and post-peak behavior stages and prevented the MICP fiber-reinforced calcareous sand from failing in a brittle failure mode which ensured the building safety.