Mechanical behavior of microbial-induced calcite precipitation (MICP)-treated soil with fiber reinforcement

Microbial cementation can effectively improve the strength of soil, but it can also lead to the obvious brittleness at soil failure. In order to balance the adverse effect of brittleness of the bio-cemented soil, a modified method of combining the fiber reinforcement with the microbial cementation is suggested. The polypropylene fibers, with mass fraction of 0%, 0.05%, 0.15%, 0.25% and 0.30%, are uniformly mixed with silica sand, then the soil samples are bio-cemented based on microbial-induced calcite precipitation (MICP). A series of unconfined compression tests are also carried out, the calcium carbonate content in each group is determined by acid pickling, and the morphological structure of fiber surfaces in soil matrix is characterized by using the scanning electron microscopy (SEM). The result shows that: (1) The fiber reinforcement can greatly improve the unconfined compressive strength and residual strength of soil samples, and can significantly improve the toughness of soil failure. (2) The fiber content has important influence on the mechanical properties of bio-cemented soil. The unconfined compressive strength with fiber content shows a trend of decrease after the first increase in general, the optimal fiber content is 0.15%, and the residual strength after peak is monotonically related with the fiber content. (3) The stress-strain curve of the microorganism solidified sandy soil is in a step-down mode, and the wave type relief features are locally exhibited. (4) The fiber reinforcement can improve the precipitation efficiency and yield of microbial-induced calcite, and at the same time, the bio-cementation effect of the calcium carbonate can promote the effect of fiber reinforcement. The combination of fiber reinforcement technology and MICP technology can realize complementary advantages, which has positive significance for improving the safety and stability of construction.