# Experimental Study on Cyclic Shear Performance of the Four-Way Geogrid Reinforcement-Soil Interface
## 3 Results and Discussion
### Shear Stress
#### 3.1.2 Effect of the Shear Displacement Amplitudes  
Figure 7 provides the shear stress-shear displacement curves for the interface between the geogrid and soil under varying shear displacements at 50, 100, 500, and 1000 cycles. In comparison of the above curves, it is evident that the area of the hysteresis loop grows with the increase in \(A_{w}\) and the number of cycles. Furthermore, when \(A_{w}\) is large, the hysteresis curve will decline with the increase in the number of cycles, resulting in strain accumulation. This degradation is obvious in the first 100 cycles and then gradually tends to be stable. \(A_{w}\) has a significant influence on the development of the peak shear stress. When \(A_{w}\) is 0.5 mm, the peak shear stress shows a trend of increasing with the increase in the number of cycles; when \(A_{w}\) is 1.5 mm, the peak shear stress shows a trend of first increasing and then decreasing with the increase in the number of cycles; when \(A_{w}\) is 2.5 mm, the peak shear stress shows a trend of decreasing with the increase in the number of cycles. When \(A_{w}\) is large, the hysteresis curve will decline with the increase in the number of cycles resulting in the accumulation of strain, and this degradation is obvious in the first 100 cycles and then gradually stabilizes. The peak value of shear stress decreases with the increase in the number of cycles. The slope of the hysteresis loop decreases with the increase in the number of cycles and decreases with the increase in the displacement amplitude.  
Figure 6: Curve of average peak shear stress under different normal stress.  
Figure 7: \(Cont.\)Figure 8 displays the curves depicting the alternating shear stress at the interface of the geogrid and soil. The curves show the changes in the average peak stress with the number of cycles for different amplitude values of displacement at a normal stress of 120 kPa and \(f\) = 0.5 Hz. The increase in \(A_{w}\) leads to an increase in both the initial shear stress and peak interface strength. When \(A_{w}\) increases from 0.5 mm to 2.5 mm, there is a 26.95 kPa increase in initial shear stress and a 32.65 kPa increase in peak interfacial strength. When \(A_{w}\) = 0.5 mm, the average peak shear stress curve increases rapidly at the beginning of the cycle and then stabilizes. However, for \(A_{w}\) values of 1.5 mm and 2.5 mm, the average peak shear stress rapidly reaches the peak strength of the interface at the beginning of the cycle and then decreases rapidly and finally stabilizes. In the shearing process, the sand particles are crushed by collision, and the crushed fine particles fill the pores between the coarse sand particles. The density of the sand particles near the interfacial shear zone increases, leading to an increase in the average peak shear stress. At the same time, the grating will be worn down by the constant collision with sand and soil, causing the peak shearing stress to decrease. When the \(A_{w}\) is small, the degree of grating wear is small and the degree of particle fracture increases with the number of cycles and then tends to stabilize, so there is an overall trend of shear hardening. When the \(A_{w}\) is larger, the particle crushing and the grating breakage become more intense, so that the peak value of the average shear stress shows a trend of hardening and then softening. The phenomenon that grids exhibit different shear properties at different shear displacement amplitudes is the same as the findings of [PERSON] et al. [28]. Moreover, the phenomenon that the interfacial residual strength decreases with increasing \(A_{w}\) can also be explained by the above point of view.  
Figure 8: Curve of peak shear stress under different shear displacement amplitudes.  
Figure 7: The hysteresis loops under different shear displacement amplitudes. (**a**) \(n\) = 50; (**b**) \(n\) = 100; (**c**) \(n\) = 500; (**d**) \(n\) = 1000.