Microbial induced carbonate precipitation (MICP) is a promising method for improving the performance of geotechnical engineering materials. However, there has been limited research on the creep characteristics of expansive soil treated with MICP. Therefore, this study investigated the improvement of consolidation creep characteristics of expansive soils using the MICP method through one-dimensional consolidation creep tests. The microstructure of the treated soil was examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results indicate that the MICP method effectively enhances the resistance of expansive soil to creep deformation. Compared to untreated expansive soil, the creep deformation of the treated soil decreased by 3.85%, 22.62%, and 18.40% for cementation solution contents of 50 mL, 100 mL, and 150 mL, respectively. Additionally, the creep curve of the improved expansive soil exhibits significant nonlinear characteristics. The creep process of the improved expansive soil can be divided into three stages: instantaneous deformation, decay creep, and stable creep. SEM images and XRD patterns reveal that the calcium carbonate precipitates generated during the MICP process can wrap, cement, and fill the voids between soil particles, which is the fundamental reason why the MICP method improves the deformation resistance of expansive soil. On the basis of the creep test results, a fractional-order creep model for MICP-treated expansive soil was established. Compared to traditional integer-order creep model, the fractional creep model can more accurately describe the entire process of consolidation creep of expansive soil improved by MICP method. The findings of this study provide a theoretical basis for analyzing the deformation of MICP-treated expansive soil under long-term loads.

Bio-mediated ground improvement techniques, including Microbial Induced Calcite Precipitation (MICP) and Enzyme Induced Calcite Precipitation (EICP) treatment methods, are extensively being employed nowadays in a variety of construction projects as newly emerging sustainable and environmentally-friendly approaches to enhance the mechanical properties and durability characteristics of earthen composites. The intrinsic brittleness of MICP- and EICP-treated soils, however, considerably limits their applications in practical geotechnical engineering. Fiber reinforcement has been widely acknowledged as an efficient solution to overcome such challenges and augment the ductility of biologically stabilized soils. Accordingly, there is growing attention to integrating natural and synthetic fibers into bio-based composites, opening up exciting possibilities for improved performance and versatility in different civil engineering applications. This review aims to examine the current state of research on utilizing fiber additives to enhance the effectiveness of MICP and EICP treatment methods in an attempt to provide an in-depth insight into the effects of fiber type, content, and length as well as the underlying mechanisms of fiber interactions within the porous structure of such treated soils. The applications of fiberreinforced bio-cemented soils, their limitations, and the major challenges encountered in practice, as well as the potential areas of interest for future research and the key factors to be considered when selecting suitable fiber for optimal soil treatment using MICP/EICP, are all critically elaborated and discussed. By synthesizing the current research findings, the study provides engineers with a valuable resource to guide the development and optimization of fiber-reinforced MICP and EICP techniques for effective soil improvement and stabilization. Based on the findings of all relevant studies in the literature, a comprehensive cost-performance-balance analysis is conducted aiming to serve as a useful guideline for researchers and practitioners interested in applying fibers in various construction projects or other related applications where either MICP or EICP technique is being utilized as the main soil stabilization approach.

Microbial-induced calcite precipitation (MICP) is an environmentally friendly treatment method for soil improvement. When combined with carbon fiber (CF), MICP can enhance the liquefaction resistance of sand. In this study, the effects of CF content (relative to the sand weight of 0%, 0.2%, 0.3%, and 0.4%) on the liquefaction resistance of MICP-treated silica and calcareous sand were investigated. The analysis was conducted using bacterial retention test, cyclic triaxial (CTX) test, LCD optical microscope, and scanning electron microscopy (SEM). The results showed that with the increase in CF content, the bacterial retention rate increased. Additionally, the cumulative cycles of axial strain to 5%, excess pore water pressure to initial liquefaction, as well as strength and stiffness, all increased with higher CF content. This trend continued up to the CF content of 0.2% for silica sand and 0.3% for calcareous sand, beyond which the cumulative cycles began to decrease. The great mechanical system of CF, calcite, and sand particles was significantly strengthened after MICP-treated. However, the reinforced calcite did not completely cover the CF, and excess CF hindered the connection between sand grains. The optimal amount of CF in silica and calcareous sands were 0.2% and 0.3%. This study provides valuable guidance for selecting the optimal CF content in the future MICP soil engineering.