# Study on Stress-Strain Relationship of Coir Fiber-Reinforced Red Clay Based on Duncan-Chang Model
## 6 Conclusions  
In this paper, the influence of coir fiber content on the strength characteristics of red clay was studied by the consolidated undrained triaxial test, and the parameters were analyzed in combination with the Duncan-Chang model. This provides an important reference value for the strength theory of coir fiber-reinforced red clay. The following conclusions were drawn:  
1. The strength characteristics of red clay can be effectively improved by adding coir fiber to the soil. Under the optimal fiber content, the failure strength of the sample is nearly three times that of plain soil.
2. When the axial strain is small, the stress-strain relationship curves of the plain soil and the coir fiber-reinforced red clay are consistent, indicating that the reinforcement effect is not obvious at this time. With the increase in axial strain, the occlusal friction between the soil and the fiber and the tensile resistance of the fiber gradually play a role, which improves the shear strength of the soil and increases the deviatoric stress of different samples.  
Figure 11: Relationship curve between initial tangent modulus and confining pressure of sample.  
3. Compared with plain soil, the cohesion of red clay mixed with fiber increases by 4.9-9.13 kPa, and reaches the maximum when the fiber content is 0.3%, while the internal friction angle of red clay mixed with fiber is not much different from that of plain soil.
4. Under the same fiber content, the parameters \(a\) and \(b\) gradually decrease with the increase in confining pressure, and the initial deformation modulus \(E_{\text{i}}\) and ultimate deviator stress \(\left(\sigma_{1}\text{--}\sigma_{3}\right)_{\text{ult}}\) of the sample increase with the increase in confining pressure. Additionally, the initial tangent modulus \(E_{\text{i}}\) increases first and then decreases with the continuous increase in fiber content. The rule of change is in line with the test situation and has guiding significance.  
Conceptualization, X.J.; Methodology, C.W.; Validation, H.Y.; Formal analysis, J.C.; Investigation, S.B.; Writing--original draft, J.G. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the Science and Technology Innovation Program of Hunan Province (Grant No.: 2022 NK2056), the National Natural Science Foundation of China (Grant No.: 31971727), the Forest Science and Technology Innovation Program of Hunan Province (Grant No.: XLK202105-3), the Special Fund of Safety Production Prevention and Emergency Response of Hunan Province in 2021 (Grant No.: 2021-QYC-10008-24956), the Hunan Provincial Natural Science Foundation Project (Grant No.: 2022 JJ31005), and the Key Construction Subject Scientific Research Ability Promotion Project of Guangdong Province (Grant No.: 2022 ZDJ5092).  
Not applicable.  
The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors thank all those who provided assistance with this study.  
The authors declare no conflict of interest.