# Post-Cyclic Mechanical Behaviors of Undisturbed Soft Clay with Different Degrees of Reconsolidation
## 4 Post-Cyclic Mechanical Characteristics of Soft Soil
### Excess Pore Water Pressure-Axial Strain Relationship  
The excess pore water pressure under various conditions is investigated in this part. Figures 9-11 represent the relationship between excess pore water pressure (\(\Delta u\)) and axial strain (\(\varepsilon\)) after cyclic loading. With the development of strain, the excess pore water pressure first increases rapidly, then decreases a little. Throughout, the undrained shear stage, the excess pore water pressure remained positive. The initial excess pore water pressure in the \(\Delta u\)-\(\varepsilon\) curve is different because the excess pore water pressure generated after cyclic loading is included in the total excess pore water pressure. Figure 8: Relationship after cyclic loading between axial deviator stress and axial strain of the soft soil with different degrees of reconsolidation (\(n=1000\), \(CSR=0.25\)): (**a**) \(p^{\prime}{}_{0}=20\) kPa; (**b**) \(p^{\prime}{}_{0}=60\) kPa. Figure 9: Variations of excess pore water pressure versus axial strain of the soft soil at different confining pressures after cyclic loading (\(n=1000\), \(CSR=0.25\), \(U_{r}=100\%\)). The post-cyclic undrained shear \(\Delta u\)-\(\varepsilon\) curves of different confining pressures are shown in Figure 9 for test conditions identical to those pertaining to Figure 5. The initial excess pore water pressure is zero because the specimens are fully reconsolidated after cyclic loading. It can be seen that, when the strain reaches a certain value, the excess pore water pressure decreases a little with increasing axial strain. Under different confining pressures, the excess pore water pressure attenuation section of the \(\Delta u\)-\(\varepsilon\) curve is nearly parallel. The attenuation values of excess pore water pressure are 6.8 kPa, 10.8 kPa, and 8.2 kPa, respectively when the confining pressures are 20 kPa, 40 kPa, and 60 kPa. At the end of the test, the greater the confining pressure, the greater the excess pore water pressure. Figure 10 shows the undrained shear \(\Delta u\)-\(\varepsilon\) curve of fully reconsolidated specimens after cyclic loading with different CSRs and \(p^{\prime}0=60\) kPa. When the strain is very small, the excess pore water pressure accumulates rapidly with increasing strain yet when the strain reaches a certain value, the excess pore pressure decreases slowly with increasing strain. This is because normally-consolidated soft clay may exhibit the properties of an over-consolidated soil after cyclic loading. It can be seen that the greater the amplitude of cyclic loading, the more obvious this phenomenon is in this soft clay. When the strain reaches 20%, the larger the CSR, the smaller the excess pore water pressure. The undrained shear \(\Delta u\)-\(\varepsilon\) curves with different degrees of reconsolidation \(U_{r}\) are shown in Figure 11. The specimen has different initial accumulated excess pore water pressures depending upon the value of \(U_{r}\). The initial excess pore water pressure during the undrained shearing process decreases with the increase of \(U_{r}\). When \(p^{\prime}0=60\) kPa and  
Figure 11: Variations of excess pore water pressure versus axial strain of the soft soil with different degrees of reconsolidation after cyclic loading (\(n=1000\), \(CSR=0.25\)): (**a**) \(p^{\prime}0=20\) kPa; (**b**) \(p^{\prime}0=60\) kPa. Figure 10: Variations of excess pore water pressure versus axial strain of the soft soil at various cyclic stress ratios after cyclic loading (\(n=1000\), \(p^{\prime}0=60\) kPa, \(U_{r}=100\%\)). the degree of reconsolidation are 0%, 50%, and 100%, the starting values of excess pore water pressure are 37.09 kPa, 24.60 kPa, and 0 kPa, respectively. The \(\Delta u\)-\(\varepsilon\) curve of the specimen with \(U_{r}=0\) has reached a steady-state in the pre-middle shear period. When the axial strain reaches a certain value, there is a peak value present in the \(u\)-\(\varepsilon\) curve: thereafter, the excess pore water pressure gradually decreases with increasing axial strain until the end of the test.