Microbial solidified sand effectively enhances the strength of the soil, but it will cause brittle failure. In order to reduce the impact of microbial solidification sand brittleness, an improved method for adding carbon fiber to microbial solidified sand is proposed. The qualitative analysis was based on unconfined compressive strength test, calcium carbonate content determination, and penetration test. The results show that the addition of fiber in the microbial solidified sand can significantly increase the unconfined compressive strength of the sample. The unconfined compressive strength of the sample increases first and then decreases with the increase of fiber addition. The addition of fibers during the soil process enhances the toughness of the specimen and causes plastic damage during the failure of the specimen. Based on the analysis of the microstructure of the sample, the effect of fiber bundles on the strength characteristics of the sample is discussed when the fiber content is higher than the optimal fiber content. The addition of carbon fiber to microbial solidified sand can greatly improve the strength of the sample and increase the toughness, which plays a positive role in improving the safety and stability of the project.

Microbially induced calcite precipitation (MICP) is an effective and ecofriendly technology that utilizes the microbes-induced mineralization to improve foundation soils of the transportation infrastructure. The carbon fiber can be used along with the MICP in order to reduce the brittleness of microbial solidified soil. This paper investigated the strength of carbon fiber-reinforced sand with different mass fractions through a series of unconfined compression tests. The effect of fiber content on the solidification of carbon fiber-reinforced sand was quantitatively analyzed using calcium carbonate content test and penetration test. The microsolidification mechanism was investigated by micrographs from the optical and scanning electron microscope (SEM). The test results showed that unconfined compressive strength generally increased first and then decreased with the increase of the fiber content. The optimal fiber content in the silica and calcareous sand was 0.2% and 0.1%, respectively. The bulging deformation of the fiber-reinforced sand sample was gradually developed along with the fiber breakage during loading.