# Study on Stress-Strain Relationship of Coir Fiber-Reinforced Red Clay Based on Duncan-Chang Model
## 1 Introduction
[28] studied the mechanical properties of coconut leaf-reinforced soil with a triaxial shear test and found that coconut leaf is a good reinforcement material for enhancing engineering performance and can be successfully used in various civil engineering applications such as slopes. [PERSON] et al. [35] used coir fiber as a reinforcement material and carried out direct shear tests, unconfined compressive strength tests, and consolidation tests to study the strength and compressibility of fiber-reinforced soil. [PERSON] et al. [36] found that randomly distributed coir fiber can significantly improve the shear strength of clay through a series of consolidated undrained triaxial compression tests. [PERSON] et al. [37] established a new procedure to determine the directional distribution of fibers in reinforced sand samples and found that the directional distribution of fibers was far from isotropic. [PERSON] et al. [38] analyzed the influence of a small number of fibers with a high aspect ratio on sandy gravel through tests in a large triaxial instrument. The constitutive model of soil was established to better reflect the strength and deformation relationship of soil. Since the Duncan-Chang model has fewer parameters and is easy to determine, it can better reflect the nonlinear characteristics of the soil, so it is widely used in mechanical properties analysis and numerical simulation of fiber-reinforced soil. [PERSON] et al. [39] studied the influence of fiber content on the Duncan-Chang model parameters of polypropylene fiber cement silty clay by triaxial compression test. [PERSON] et al. [40] constructed a modified Duncan-Chang model that can reflect the influence of the polyester fiber yarn blending ratio through the analysis of triaxial shear test data. [PERSON] et al. [41] studied the strength characteristics of fiber-reinforced soil under different polypropylene fiber content and confining pressure through triaxial tests, and used the Duncan-Chang model to describe its stress-strain relationship and proposed a calculation method to determine the model parameters. [PERSON] et al. [42] studied the influence of polyvinyl alcohol fiber on the engineering properties of solidified silt and Duncan-Chang model parameters through a series of triaxial tests. [PERSON] et al. [43] mixed polypropylene fibers with different mass ratios into coal gangue-modified expansive soil for triaxial consolidation drainage tests and used MATLAB software to obtain the fitting function of fiber content and confining pressure to model parameters \(a\) and \(b\), and verified the fitting degree of the Duncan-Chang model. Most of the published literature on the reinforcement of soil with randomly distributed coir fiber is currently related to the reinforcement of non-cohesive or granular soil. There has been limited research on the use of randomly distributed coir fiber in cohesive soil, and very little work has been done in combination with the Duncan-Chang model. In order to make coir fiber more applicable to slope engineering, this paper mainly discusses the stress-strain relationship and strength characteristics of coir fiber-reinforced soil under different fiber content and confining pressure through the consolidated undrained triaxial shear test and studies the influence of fiber content and confining pressure on Duncan-Chang model parameters.