# Behavior of Fiber-Reinforced and Lime-Stabilized Clayey Soil in Triaxial Tests
## 3 Results and Discussion
### Stress-Strain Relation  
Deviatoric stress-axial strain relations for untreated soil, lime-stabilized soil, fiber-reinforced soil, and fiber-reinforced soil stabilized with lime are shown in Figure 2. Note that the deviatoric stress-axial strain relations for treated soil are discussed for only one confining pressure (i.e., 200 kPa) due to the similarity of the stress-strain behavior between different confining pressures. It can be seen that untreated soil and fiber-reinforced soil exhibit strain-hardening behavior while strain-softening occurs in lime-stabilized soil and fiber-reinforced soil stabilized with lime. The strain-softening behavior of fiber-reinforced soil stabilized with lime is not as severe as that of lime-stabilized soil comparing Figure 2b with Figure 2d, indicating that the addition of wheat straw fibers into lime-stabilized soil contributes to the change of the stress-strain behavior of lime-stabilized Hefei clayey soil from strain-softening to a more ductile one. The magnitude of this contribution varies depending on fiber content at a constant lime content and seems to increase with increasing fiber content from 0.2% to 0.4% and then decrease slightly when further increasing the fiber content. Therefore, the optimum fiber content for the fully mobilized fiber to improve the strain-softening behavior of the lime-stabilized soil is approximately 0.4%. The shear strength of the tested samples also displays the difference in the effects of fiber reinforcement, lime stabilization, and a combination of them. The effect of fiber reinforcement on the shear strength is of benefit subjected to the control of an upper bound. The upper bound is an increase of 133.7 kPa in the shear strength achieved by the addition of 0.4% fibers. A higher amount of fibers tends to induce segregation and tangling of fibers which jeopardizes the effective interaction of fibers and soil particles. Lime stabilization enormously increases the shear strength of Hefei clayey soil. When the lime contents were 2%, 4%, and 6%, the shear strengths of the samples were 243.2, 307.8, and 226.2 kPa, respectively. The increases in shear strength brought by lime stabilization are almost 2 times that derived from fiber reinforcement. A combination of 0.4% fiber reinforcement and 4% lime stabilization produces a 322.2 kPa strength increase compared to the shear strength of untreated soil, which is smaller than the sum of strength increase brought by 0.4% fiber reinforcement (133.7 kPa) and the strength increase caused by 4% lime stabilization (307.8 kPa). This difference in strength increase indicates that the combined effect of fiber reinforcement and lime stabilization is not a simple summation of their respective effects. Therefore, the effect of fiber reinforcement and that of lime stabilization are coupled. This coupling effect can be accounted for through SEM analysis.  
Figure 2: Stress–strain relations for untreated soil tested at various confining pressures and treated soil tested at 200 kPa: (**a**) untreated soil, (**b**) lime-stabilized soil, (**c**) fiber-reinforced soil, and (**d**) fiber-reinforced soil stabilized with lime.