# Post-Cyclic Mechanical Behaviors of Undisturbed Soft Clay with Different Degrees of Reconsolidation
## 2 Test Samples and Experimental Program
### Experimental Scheme and Procedures  
The whole test process is shown in Figure 3. First, the tested specimens are saturated by vacuum and back-pressure saturation. The vacuum was held for 4 h, then air-free distilled water was injected until the specimens were submerged; then, all specimens were soaked for more than 24 h. On this basis, the specimen was placed in the pressure chamber and saturated by way of back-pressure saturation. When Skempton's \(B\) value reached 0.95 (or more), saturation was deemed to be completed. Next, the sample was subjected to isotropic consolidation under a certain consolidation confining pressure. Since the coefficient of permeability of such a soft soil is small and the dissipation of excess pore water pressure is slow, it is considered that the consolidation of soil is completed when the drainage volume is less than 100 mm\({}^{3}\)/h. To analyze the effect of the confining pressure on the shear characteristics after cyclic loading, the confining pressure was set to 20 kPa, 40 kPa, and 60 kPa, in turn. Cyclic triaxial tests were conducted on the consolidated soil under undrained conditions. The amplitude of cyclic deviatoric stress is described by cyclic stress ratio (CSR) proposed by [PERSON] et al. [20]. \[\text{CSR}=q^{\text{ampl}}/2{p^{\prime}}_{0}=q^{\text{ampl}}/2\sigma_{3}^{\prime} \tag{1}\]  
where \({p^{\prime}}_{0}\) represents the effective mean stress after consolidation and \(q^{\text{ampl}}\) is the amplitude of the cyclic deviator stress. Herein, when the effects of confining pressure and the degree of reconsolidation on the shear characteristics of soil after cyclic loading are considered, the  
Figure 3: Loading process applied to the specimens. Figure 2: Dynamic triaxial test system. CSR of 0.25 is employed, implying that the amplitude of the cyclic deviator stress applied to the specimen is half of the effective radial pressure. To facilitate the investigation into the effect of CSR, the effective confining pressure is set to 60 kPa, i.e., the CSR values are 0.083, 0.167, 0.250, and 0.333, respectively. All specimens were subjected to cyclic loading with half-sine wave. Moreover, the number of cycles \(n\) is 1000. To obtain more accurate pore water pressure, the loading frequency is 0.1 Hz. Following that, the specimens subjected to cyclic loading were reconsolidated. Among that, specimens with different reconsolidation degrees can be obtained. The degree of reconsolidation (\(U_{r}\)) of the sample is defined by the degree of dissipation of excess pore water pressure induced during cyclic loading. As shown in Equation (2), after cyclic loading, back-pressure \(p_{u}\) is applied to the specimen, and the accumulated excess pore water pressure dissipates to \(p_{u}\) and then remains unchanged. Among that, the sample with \(U_{r}\) = 0 corresponds to the sample without reconsolidation, while \(U_{r}\) = 100% corresponds to the sample with complete reconsolidation. \[U_{r}=1-\frac{p_{u}}{(\Delta u)_{cy}} \tag{2}\]  
where \((\Delta u)_{cy}\) represents the excess pore water pressure induced during cyclic loading; \(p_{u}\) is back pressure applied to the specimen during the reconsolidation process. After reconsolidation, the specimens were subjected to strain-controlled undrained shearing. To study the effect of cyclic loading history on the shear characteristics of soft soil, the undrained shear strength (as measured by static triaxial testing) of specimens without cyclic loading history was compared. The shear failure was deemed to occur at 20% of the axial strain, and the whole shear process was set to last for 200 min (shearing rate was 0.1%/min) according to the Ministry of Water Resources of the Peoples' Republic of China (2019). The undrained shear strength of specimens with and without cyclic loading history is defined as half of the peak deviatoric stress when the axial strain reaches 20%, as denoted by \(S_{c,cu}\), and \(S_{cu}\), respectively.