## 4 Results and Discussion  
### Relationship between Deviatoric Stress and Axial Strain  
Figure 7 delineates the deviatoric stress-axial strain curves of the SCL samples at confining pressures of 150, 250, and 400 kPa and different numbers of sand layers. As can be seen in Figure 7, the SCL samples (\(n=1,\,2,\,3\)) have a higher peak stress (\(\sigma_{\text{P}}\)) under specific confining pressures than the pure clay sample (\(n=0\)). The \(\sigma_{\text{P}}\) of the samples also enlarges with an increase in the number of sand layers. It should be noted that increasing \(n\) gradually reduces the strain-softening degree of the samples but enlarges the axial strain (\(\epsilon_{\text{n}}\)) corresponding to the \(\sigma_{\text{P}}\). The smaller the confining pressure is, the more significant the increasing trend of the \(\epsilon_{\text{n}}\) corresponding to the \(\sigma_{\text{P}}\) with \(n\) becomes. The above results demonstrate that laying the sand layers in the sample can significantly improve the post-peak characteristics of the samples; furthermore, the larger the number of sand layers is, the more pronounced the effect becomes. In practical engineering, the sand layers can be laid in the clay filler, which can effectively avoid the sudden damage to the soil structure caused by the rapid decrease in its strength during large deformations, thereby improving the safety of the soil structure. Figure 6: The scheme for the numerical triaxial compression test on the LGSCR samples: (**a**) different numbers of layers; (**b**) different thicknesses of layers. Figure 7: _Cont._Figure 8 depicts the deviatoric stress-axial strain curves of the SCL samples at confining pressures of 150, 250, and 400 kPa and different thicknesses of sand layers. As can be seen from the figure, increasing the thickness of sand layers raises the \(\sigma_{\text{p}}\) of the SCL samples under a specific confining pressure but reduces their strain-softening degree. The \(\varepsilon_{\text{n}}\) corresponding to the \(\sigma_{\text{p}}\) also increases with \(t\), but the increasing trend is not noticeable. The above results confirm that when only one layer of the sand is laid in the sample, increasing the thickness of the sand layer can only slightly reduce the post-peak, strain-softening degree of the samples and cannot effectively delay the occurrence of the peak stress. In actual projects, the laying method of _thin multi-sand layers_ should be adopted. Figure 7: The deviatoric stress–axial strain curves of the SCL samples with different numbers of sand layers and confining pressures of (**a**) 150 kPa, (**b**) 250 kPa, and (**c**) 400 kPa. Figure 8: The deviatoric stress–axial strain curves of the SCL samples at different thicknesses of sand layers and confining pressures of (**a**) 150 kPa, (**b**) 250 kPa, and (**c**) 400 kPa. Figure 9 delineates the deviatoric stress-axial strain curves of the LGSCR samples at confining pressures of 150, 250, and 400 kPa and with different numbers of sand layers. As can be seen in this figure, the strength of the LGSCR samples under a specific confining pressure rises significantly with an increase in the number of sand layers. At the 150 kPa confining pressure, the elastic region behavior and the apparent initial tangent modulus of the four LGSCR samples have obvious differences. This phenomenon occur because the geogrid-reinforced sand layers have a negative dilatancy behavior, which is followed by a dilatancy behavior at a low confining pressure. Compared with the SCL samples, the LGSCR samples have a higher \(\sigma_{\text{p}}\) at the same \(n\) value. Raising the number of sand layers gradually declines the strain-softening degree of the LGSCR samples but further enlarges the \(\epsilon_{\text{n}}\) corresponding to the \(\sigma_{\text{p}}\) compared with the SCL samples. The above results demonstrate that laying the geogrid in the sand layer can effectively improve the \(\sigma_{\text{p}}\) of the samples and further enhance their ductility.