# Investigation of the Mechanical Behavior of Polypropylene Fiber-Reinforced Red Clay
## 1 Introduction
Many studies on the influence of \(FL\) and \(FC\) on the shear strength and tensile strength of reinforced soil have been carried out. Based on the reverse direct shear test, [PERSON] et al. [8] indicated that the shear strength increased with an increase in \(FC\) and \(FL\), whereas the rate of increase decreased with the number of cycles. [PERSON] and [PERSON] [9] concluded that the ductility, toughness, and resistance to tensile of clays improved with the addition of short fibers. [PERSON] [23] indicated that fiber addition results in the increased compressive and tensile strength of stabilized soil, and the shrinkage limit and crack reduction increased as \(FC\) and \(FL\) increased. [PERSON] et al. [24] demonstrated that the dynamic shear modulus of fiber-reinforced clay decreased as cell pressure increased, whereas the damping ratio increased with increasing shear strain and \(FC\). [PERSON] et al. [25] concluded that the cracking intensity factor of fiber-reinforced clay improved as \(FC\) increased, whereas the effect on surface contraction was non-significant. Meanwhile, the UCS and shear strength initially increased and then decreased as \(FC\) increased. Fiber-reinforced soil improves the strength of soil in a freeze-thaw cycle environment. [PERSON] et al. [11] noted that the static and dynamic tensile strength of clay exposed to a freeze-thaw effect was obviously increased by the adjunction of basalt fiber, and the tensile strength did not continuously decrease with the freeze-thaw cycles. Red clay--a high-plasticity clay formed by the strong chemical weathering of carbonate rocks, which are widely distributed in China (e.g., the Yunnan-Guizhou Plateau, eastern Sichuan, Hunan, Hubei, northern Guangdong, and northern Guangxi)--severely affects foundation stability because of its high water content, high plasticity index, large void ratio, and susceptibility of shrinkage and cracking. Thus, red clay foundations must be appropriately treated prior to the construction of superstructures. [PERSON] et al. [26] studied the mechanical characteristics of red clay reinforced by glass fiber with different contents by conducting unconfined compression tests and using the discrete element method. They concluded that the addition of glass fiber slowed the rapid development of cracks in the soil and increased the compressive strength of reinforced soil. With an increase in \(FC\), the damage degree of the reinforced soil decreased, the susceptibility of the reinforced soil to local failures along the fiber-soil interface enlarged, and the compressive strength of the reinforced soil decreased. [PERSON] et al. [27] reinforced red clay with different contents of lignin fiber and found that, with an increase in \(FC\), the modulus of compression of reinforced red soil initially increased and then decreased, the internal friction angle (\(\varphi\)) basically did not vary, and the cohesion (\(c\)) exhibited a decrease-increase-decrease variation pattern. [PERSON] and [PERSON] [28] found that the addition of certain amounts of glass fiber and lime into red clay resulted in a notable increase in the modulus of compression, and the addition of lime resulted in a larger increase in the modulus of compression than the addition of glass fiber. The modulus of compression of the fiber-reinforced soil initially increased and then decreased with increases in \(FC\) and \(FL\), peaking at an \(FC\) of 1% and an \(FL\) of 9 mm. [PERSON] et al. [6] demonstrated that the unconfined compressive strength of a polypropylene fiber-reinforced soil increased as \(FC\) and \(FL\) increased and was 1.18 to 2.54 times that of plain soil. Fiber could ameliorate the residual strength and resistance to failure of red clay and alter the failure mode from brittle to plastic. This change occurs because the fiber forms a spatial network structure in the soil that serves to confine the deformation and improves the integrity of the soil.