# Post-Cyclic Mechanical Behaviors of Undisturbed Soft Clay with Different Degrees of Reconsolidation
## 4 Post-Cyclic Mechanical Characteristics of Soft Soil  
### Stress-Strain Relationship  
In this section, the stress-strain relationship with different degrees of reconsolidation and cyclic loading history is discussed. Figures 6-8 show the post-cyclic undrained shear stress-strain (\(q\)-\(\varepsilon\)) relationship curves of specimens with different degrees of reconsolidation: the trend of stress-strain curves are similar. When the strain is low, the stress increases rapidly within a small range of strains, then, with increasing strain, the stress increases slowly and the non-linearity of the \(q\)-\(\varepsilon\) curves becomes more apparent. When the axial strain reaches 20%, the deviatoric stress tends to be stable. Since the strain generated after the cyclic loading is measured in terms of the total strain, the starting strain of the \(q\)-\(\varepsilon\) curves is different. Figure 6 illustrates the post-cyclic stress-strain curves of the fully reconsolidated specimens (\(U_{r}=100\%\)) with different confining pressures and the curves of specimens without cyclic loading history are also plotted for comparison. It can be seen that, the greater the confining pressure, the greater the static shear strength \(S_{cu}\) and post-cyclic shear strength \(S_{c,cu}\). Moreover, the post-cyclic shear strength \(S_{c,cu}\) is larger than the static shear strength \(S_{cu}\) at a given confining pressure. For example, when the consolidated confining pressure is 40 kPa, the corresponding post-cyclic shear strength and the static shear strength are 40.9 kPa, and 33.5 kPa, respectively. Figure 5: Test results of the soft soil under cyclic loading at various consolidated confining pressures: (a) \(\varepsilon_{a,t}\)-\(t\); (b) \(\Delta u\)-\(n\). The effect of the cyclic stress ratio (CSR) on the stress-strain relationship was investigated. Figure 7 shows the post-cyclic \(q\)-\(\epsilon\) curves of fully reconsolidated specimens with \(n=1000\) and \(p^{\prime}{}_{0}=60\) kPa. The results of the undrained triaxial shear test without cyclic loading history at a confining pressure of 60 kPa are also shown for comparison. As shown in Figure 7, in general, under the same test conditions, the initial strain increases with the CSR. This is mainly attributed to the promotional effect of cyclic deviator stress on the development of axial strain. When the amplitudes of the cyclic deviator stress are 10 kPa, 20 kPa, 30 kPa, and 40 kPa, the corresponding initial strain are 0.24%, 0.43%, 0.66%, and 4.27%, respectively. When the CSR is small, the difference between post-cyclic shear strength \(S_{c,cu}\), and static shear strength \(S_{cu}\) can be ignored; however, with the increase of the CSR, the post-cyclic shear strength of the specimen becomes significantly greater than the static shear strength. For example, when the amplitudes of cyclic deviator stress increase from 10 kPa to 40 kPa, the difference between post-cyclic shear strength and the static shear strength increases from \(-0.9\) kPa to 9.3 kPa. Figure 8 shows the post-cyclic \(q\)-\(\epsilon\) curves of the specimens with different degrees of reconsolidation \(U_{r}\). Among that, the CSR = 0.25, \(p^{\prime}{}_{0}=20\) kPa, and 60 kPa, respectively. The peak stress of \(q\)-\(\epsilon\) curves varies with \(U_{r}\). In general, the greater \(U_{r}\), the greater the  
Figure 6: Relationship between axial deviator stress and axial strain of the soft soil with different confining pressures (\(n=1000\), \(CSR=0.25\), \(U_{r}=100\%\)). Figure 7: Relationship between axial deviator stress and axial strain of the soft soil with different cyclic stress ratio (\(n=1000\), \(p^{\prime}{}_{0}=60\) kPa, \(U_{r}=100\%\)). post-cyclic shear strength \(S_{c,cu}\). For example, when the \(U_{r}\) increase from 0% to 100% with \(p^{\prime}{}_{0}=60\) kPa, respectively, the corresponding post-cyclic shear strength increases from 27.8 kPa to 39.5 kPa.