The Strength Law of Coconut Shell Fiber–Reinforced Soils Based on the Hardin–Drnevich Model

Abstract

A large diameter triaxial specimen of 61.9 mm was made by mixing coconut shell fibers with red clay soil. The shear strength of coconut shell fiber–reinforced soil was investigated using a dynamic triaxial shear test with confining pressure in a range of 50–250 kPa, a fiber content of 0.1%–0.5%, and a loading frequency of 0.5–2.5 Hz. The Hardin–Drnevich model based on the coconut shell fiber–reinforced soil was developed by analyzing and processing the experimental data using a linear fitting method, determining the model parameters a and b, and combining the influencing factors of the coconut shell fiber–reinforced soil to improve the Hardin–Drnevich model. The results show a clear distinction between the effects of loading frequency and fiber content on the strength of the specimens, which are around 1 Hz and 0.3%, respectively. Hardin–Drnevich model based on coconut shell fiber–reinforced soil can better predict the dynamic stress-strain relationship of coconut shell fiber-reinforced soil and reflect the dynamic stress-strain curve characteristics of the dynamic stress-strain curve coconut shell fiber-reinforced soil. Coconut shell fiber is a type of natural fiber material that boasts the advantages of being renewable and exhibits excellent tensile properties. When incorporated into soil, coconut shell fibers can interconnect with soil particles to form a new soil structure. This novel soil structure possesses enhanced shear strength and flexibility, significantly improving the cohesion and internal friction angle of red clay. In this study, we conducted triaxial tests using large-sized triaxial specimens to investigate the effects of coconut shell fiber content, fiber length, vibration frequency, confining pressure, and other factors on the static and dynamic characteristics of coconut shell fiber–reinforced soil. A thorough analysis of each influencing factor was performed. Based on these analyses, static and dynamic constitutive models for coconut shell fiber–reinforced soil were established. Subsequently, the model parameters obtained from the static and dynamic triaxial tests, along with specific boundary conditions from real-world engineering projects, were input into the Midas GTS/NX (version 2019) slope modeling software. Numerical simulations were then carried out for both unreinforced soil slopes and slopes reinforced with coconut shell fibers. This process culminated in a safety verification of the coconut shell fiber–reinforced slopes. The findings of this research provide critical insights and serve as an important reference for the future application of coconut shell fiber–reinforced soil in engineering practices. The results not only validate the effectiveness of coconut shell fibers in enhancing slope stability but also offer a promising approach for sustainable geotechnical engineering solutions.