Recent research has focused on reinforcing sand consolidated through microbial -induced carbonate precipitation (MICP) with alkali -treated fibers to enhance its mechanical properties and mitigate brittleness. This research investigated how modified fiber affected the microstructure and properties of MICP solid sand. The fiber content (0, 0.5, 1, 3, and 5%), pretreatment concentration (0, 1, 5, 10, and 20%), pretreatment time (0, 0.5, 1, 2, and 4 h), and pretreatment temperature (25, 35, 45, and 55 degrees C) required for the experiment were determined by MICP testing. The interactions between fiber, sand, and calcium carbonate(CaCO3) were analyzed by calcium carbonate content(CaCO3(%)), unconfined compressive strength (UCS), environmental scanning electron microscopy (ESEM), and X-ray diffraction (XRD). The specimen without added fiber had a UCS of 2.13 MPa, the UCS of the added fiber sample was 2.8 MPa, which was 31.46% more than that of the specimen without added fiber, and the UCS of the specimen with added alkali -treated fiber was 3.62 MPa, which was 70% more than that of the specimen without added fiber and 28.57% more than that of the added untreated fiber. The optimum content of jute fibers was 0.5%, and the optimum concentration of alkali treatment of jute fibers was 10% for one hour.

In recent years, microbial mineralization has aroused attention in soil reinforcement. However, most studies focus on soil and coast on land, and the consolidation of seafloor sediments is rarely reported. In this paper, the hydrate reservoir sediments in different sea areas are strengthened, which provides a new method to solve the formation settlement problem in hydrate exploitation. In this study, the microorganisms were cultivated using both fresh and seawater, and hydrate sediments of varying particle sizes (fine sand and silty sand) were consolidated. Triaxial tests and calcium carbonate content tests were conducted to characterize the consolidation effect and detect calcium carbonate content. X-ray diffraction was used to analyze the crystal form and mineral composition of calcium carbonate generated. SEM was employed to observe the microscopic characteristics of the consolidated samples. X-ray computer tomography (X-ray CT) was utilized to analyze changes in pore throat size and the distribution of calcium carbonate in different samples and environments. The experimental results indicate that the consolidated samples exhibit higher strength, particularly in a seawater environment. Fine sand sediment samples primarily demonstrate increased cohesion, from 3.7 kPa initially to 42.3 and 86.8 kPa after consolidation, with the friction angle increasing by less than 2 degrees. While silty sand sediment samples exhibit a greater increase in friction angle after cementation, from 22 to 24.9 degrees and 27.6 degrees, and the cohesion increased by only about 6%. Additionally, it was discovered that the increase in sample strength is not only related to the calcium carbonate content but also to the crystal form and distribution of calcium carbonate within the samples. Under identical sample conditions, those treated in a seawater environment exhibit a more uniform distribution of calcium carbonate and a greater abundance of calcium carbonate crystal forms, such as calcite and vaterite. Furthermore, after consolidation, among the samples treated with fresh water, the porosity of the fine sand sample decreased from 46.38 to 18.26%, and that of the silty sand sample decreased by 25.62%, indicating that fine sand and silty sand samples still possess connecting pores that are not completely obstructed by calcium carbonate. This provides a pathway for improving grouting cycles and gas release following hydrate decomposition.