Due to their advantages of high rupture strength and long service life, polymer fibers are often used for soil improvement. However, there is no consensus on how the mixing of discrete polymer fibers affects the stress-strain relationship of clays. In this study, a constitutive relationship of polymer fiber-reinforced clay was established on the basis of the stress-strain relationship between clay and polymer fibers. The elastic-plastic unified hardening (UH) model was employed, and the fiber contribution was introduced based on the UH model. The constitutive relationship of polymer fiber-reinforced clay considers the anisotropic distribution of the discrete fiber orientation and the relative sliding between the fibers and clay matrix. The model was verified by referring to the results of consolidated undrained (CU) and consolidated drained tests of typical polymer fiber-reinforced clays in previous studies. A series of CU tests on rubber fiber-reinforced clay were conducted to validate the model further. The ratio of the simulated results to the experimental results gradually approached 1 with increasing axial strain. The constitutive relationship of polymer fiber-reinforced clay could provide satisfactory results. Polymer fiber mixing increases soil strength and enhances the properties of problematic soils, which makes the problematic soils more valuable for engineering applications. Studies have shown that the fibers in the soil tend to be distributed horizontally after the compaction process. With the anisotropic distribution of fiber orientation considered, the authors established a numerical calculation method for the stress-strain relationship of polymer fiber-reinforced clay. A major objective of this work was to allow the use of computerized numerical analysis methods when performing mechanical analyses of polymer fiber-reinforced clay, which avoids the need to conduct a large number of shear tests. In this study, a series of consolidated undrained tests of rubber fiber-reinforced expansive clay were conducted. With the data collected, the numerical calculation method for the stress-strain relationship of polymer fiber-reinforced clay was verified, and the numerical results agreed with the test results better.

Reinforcement of soils with fibers generally increases the mechanical properties of the fiber-reinforced soil (FRS) system. However, published literature is limited to investigating the undrained response of clay and synthetic fibers, with few studies targeting natural clay and natural fibers under drained conditions. There is a need to study the response of fiber-reinforced clay systems under drained conditions to assess long-term stability. This paper investigated the drained shear strength and durability of clays reinforced with natural hemp fibers using isotropically consolidated drained triaxial tests, in which the fiber content, confining pressure, and compaction water content were varied. Results showed that the incorporation of hemp fibers improved the deviatoric stress at failure by up to 60%, which increased the drained cohesion and friction angle of the FRS by 7-10 kPa and 3-7 degrees, respectively. The increase in cohesive intercept was not affected by the compaction water content, while the increase in friction angle was pronounced in specimens compacted at optimum water content (w = 18%). Durability tests showed that the improvement in strength due to hemp fibers diminishes after 3 weeks of curing prior to drained testing, indicating the dramatic negative impact of degradation of natural fibers on the mechanical performance of fiber-reinforced clay and the need for industrial treatment of the fiber.