Dynamic behavior of microbial-induced calcite precipitation improved loess soil with basalt fiber reinforcement using cyclic direct simple shear test

Loess soil consists of fine-grained sediments deposited by wind, creating a porous structure that can be significantly affected by changes in hydro-mechanical loading conditions. Furthermore, due to its composition primarily consisting of silty deposits, loess soil is susceptible to erosion induced by water or air movement. This study aims to improve the strength and dynamic properties of loess soil by an efficient and environmentally friendly method called microbial-induced calcite precipitation (MICP), which is a proper alternative for using materials incompatible with nature, such as lime, cement, and chemical substances in soil. Sporosarcina pasteurii with an optical density of 1 has been used for microbial calcite cementation. The effects of curing time (3, 7, and 28 days) and various normal stress levels (100, 200, and 300 kPa) at shear strain amplitudes in a range of 0.05% to 1% have been investigated. Also, 1.5% natural basalt fiber has been considered to promote the performance of MICP. A series of unconfined compressive strength (UCS), cyclic direct simple shear (CSS), and bender element tests have been conducted to evaluate the dynamic characteristics such as shear modulus (G), damping ratio (D), and small-strain shear modulus (\(\:{\text{G}}_{\text{max}}\)) of natural soil and treated ones. Scanning electron microscopy (SEM) has been used to confirm the results. The results indicated the positive effects of the employed treatments on the dynamic characteristics of loess soil. Utilizing the MICP technique and the MICP with basalt fiber has enhanced the shear modulus of the loess soil by up to 25% and 49%, respectively.