###### Abstract  
Benefiting from low cost, high tensile strength, chemical stability, and great resistance to temperature, alkaline, and acids, it is a reasonable and valuable technology to use basalt fiber (BF) as an admixture to optimize building materials. So far, the challenge is still to master the engineering performance of BF-reinforced materials, especially poor subgrade soils. To this end, this paper carried out a series of unconfined compressive strength (UCS) tests, splitting tensile strength (STS) tests, and scanning environmental microscope (SEM) tests to study the mechanical properties and microstructure mechanism of BF-reinforced subgrade cemented silty sand with different fiber contents and curing times. The aims of this research were: (i) the UCS and STS of basalt fiber reinforced uncemented silty sand (BFUSM) and basalt fiber reinforced cemented silty sand (BFCSM) both increased with the increase of curing time and the strength reached the maximum value after curing for 28 days; (ii) the optimal fiber content was 0.2%, and a good linear correlation existed between UCS and STS; (iii) from the microscopic point of view, the combination of BF and cement could combine the physical action of fiber reinforcement and the chemical action of cement hydration reaction to form a fiber-cement-soil skeleton structure to improve the strength of silty sand and the improvement effect after working together was better than separately incorporated BF or cement; and (iv) the corresponding developed multiple nonlinear regression (MNLR) models which can well predict UCS and STS of BFUSM and BFCSM were established. basalt fiber reinforced cemented silty sand (BFCSM); unconfined compressive strength (UCS); splitting tensile strength (STS); microscopic mechanism; multiple nonlinear regression (MNLR) models +
Footnote †: journal: Applied Sciences  
Stable soil can meet the needs of engineering technology and is widely used in geotechnical engineering. In the past, most of the domestic and foreign choices focused on stabilizers made of inorganic binder materials, such as cement, lime, and fly ash, and the properties of the stabilized soil are already mature and reliable through numerous research, which could provide guidance for construction and be widely used in the treatment of soft foundations and road and railway foundations [11; 12; 13; 14; 15]. As we all know, the stabilizing effects of cement are better among inorganic binder materials [16; 17; 18]. However, cement is one of the many causes the CO\({}_{2}\) emissions [19]. As a result, attention to fiber-reinforced cemented soil has arisen in recent years. The relevant literature has already confirmed that the incorporation of fiber will give the soil better physical and mechanical properties [20; 21; 22; 23; 24; 25; 26]. For fiber reinforcement, the common fiber types are basalt fiber (BF), polypropylene fiber, glass fiber, lignin fiber, cornsilk fiber, and carbon fiber. Among these, BF as an economical and environmentally friendly inorganic material, produced by melting and stretching natural volcanic basalt rock at 1450-1500 \({}^{\circ}\)C, has many advantages, such as high tensile strength and chemical stability. Moreover, BF is cheaper than glass fiber or carbon fiber since it is consumed less and has no additives [27; 28]. Furthermore, the chemical properties of BF are similar to that of cement, thus the bond strength between them is better [29]. Therefore, it has been widely used to reinforce the mechanical properties of concrete and asphalt concrete [30; 31; 32; 33; 34; 35]. Similarly, the incorporation of BF can also contribute to improving the strength properties of plain soil and cemented soil, which enhances the bonding between the particles and the fibers and weaken the void ratio. Furthermore, the improvement effect of the cement and fiber combination is better than the effect of only incorporated BF or cement [36; 37].