# Behavior of Fiber-Reinforced and Lime-Stabilized Clayey Soil in Triaxial Tests
## 3 Results and Discussion
### Microstructural Mechanisms of the Coupling Effect  
The coupling effect of wheat straw fiber reinforcement and lime stabilization on the stress-strain relation, shear strength parameters, secant modulus, and failure pattern of treated Hefei clayey soil has its explanation in microstructural mechanisms which can be captured through SEM analysis. SEM micrographs showing the honeycomb pattern of wheat straw fibers are shown in Figure 7. Figure 8 shows the SEM micrographs for lime, wheat straw fiber surface wrinkles due to friction, untreated soil, fiber surface morphologies in fiber-reinforced soil and fiber-reinforced soil stabilized with lime, and soil particle morphology in lime-stabilized soil. It can be observed from Figure 8b that the mobilization of the fiber reinforcing effect is driven by friction developed during physical contact between soil particles and the fiber surface. This physical contact can be also inferred from the experimental evidence presented in Figure 9.  
The mechanism of stabilizing soil with lime is tripartite. First, the water within the soil reacts with the added lime, which reduces the soil moisture content and thus speeds up the soil consolidation process. Second, the sandification effect due to the addition of lime causes hydrophobic behavior in the soil particles, which can restrain the formation of soil particle packets and densify the soil fabric. Third, the chemical reaction of lime and soil produces a vast number of cementitious gels which fill most of the distributed pores and bind soil particles together (as shown in Figure 10), creating a denser soil fabric. The soil fabric improved by lime through these three ways is reflected in the final soil particle morphology shown in Figure 8e.  
Figure 7: SEM micrographs of the wheat straw fiber’s honeycomb pattern ((**a**) magnification of 250\(\times\); (**b**) magnification of 1000\(\times\); and (**c**) magnification of 8000\(\times\)) and the wheat straw fiber surface ((**d**) magnification of 800\(\times\)).  
The simultaneous existence of fiber and lime within a sample of fiber-reinforced soil stabilized with lime creates a more effective fiber reinforcing effect and faster lime stabilization development than when they exist alone. Because of the water channels offered by the surfaces and honeycomb pattern (as shown in Figure 7) of wheat straw fibers, the process of the chemical reaction between lime and water becomes faster, causing a higher secant modulus then when lime exists alone. On the other hand, more effective contact between fibers and soil particles for fiber-reinforced soil stabilized with lime can  
Figure 8: SEM micrographs showing (**a**) lime; (**b**) a fiber surface wrinkle; (**c**) untreated soil; (**d**) the fiber surface morphology in 0.4% fiber-reinforced soil; (**e**) the soil particle morphology in 4% lime-stabilized soil; and (**f**) the fiber surface morphology in 0.4% fiber-reinforced soil stabilized with 4% lime.  
be noticed in the comparison between fiber surface morphologies presented in Figure 8d,f. The reason for this is that the three ways by which lime stabilization functions contribute to denser soil fabric and a smaller volume of soil particle packets. Besides this, the coverage of cementitious gels produced by the presence of lime on wheat straw fiber surfaces can improve the physical interaction between fibers and soil particles because of the increased friction coefficient caused by the high surface roughness and rigidity of these cementitious gels.