## 3 Results and Discussion
### Isotropically and \(K_{0}\) Consolidated Samples Test Results
The excess pore water pressure had greater amplitude than in test 2.1 but this phenomenon was caused by greater deviator stress amplitude \(q_{a}\). Samples 2.3 and 2.4 (Figures 7 and 8) were consolidated in K\({}_{0}\) stress conditions and with a confining pressure \(\sigma^{\prime}{}_{3}\) equal to 139.7 and 94.2 kPa respectively. The pore pressure response to cyclic loading in the case of sample 2.3 (\(q_{a}\) equal to 10.4 kPa)  
Figure 5: Results of the cyclic triaxial test for sandy silty clay under a confining pressure of 65 kPa and under the \(K_{0}\) consolidation, initial void ratio \(\epsilon_{0}\) = 0.333, \(K_{0}\) = 0.67—sample 2.1: (**a**) Excess pore water pressure versus vertical strain characteristic, (**b**) excess pore water pressure characteristic versus number of cycles, (**c**) vertical strain characteristic versus number of cycle, (**d**) deviator stress–vertical strain relationship, and (**e**) the deviator stress–mean effective stress relationship (red color—last 10 cycles; arrow color—violet: Saturation phase, green: Consolidation phase, blue: Cyclic loading program). was higher than in the case of sample 2.4 (\(q_{a}\) equal to 15.8 kPa). The cause of this phenomenon was the lower initial void ratio \(e_{0}\) in the case of sample 2.4 (\(e_{0}=0.276\)) than in sample 2.3 (\(e_{0}=0.379\)). The greater density of sample 2.4 resulted in lower pore pressure generation. Nevertheless, plastic strain accumulated in sample 2.4 with a higher rate than in sample 2.3. In sample 2.2 (on Figure 6 with \(e_{0}=0.399\)\(\sigma^{\prime}{}_{3}=125.0\) kPa, and \(q_{a}=13.5\) kPa), the plastic strain accumulation was close to what could be observed in the case of sample 2.3. Figure 6: Results of the cyclic triaxial test for sandy silty clay under a confining pressure of 125 kPa and under the \(K_{0}\) consolidation, initial void ratio \(e_{0}=0.399\), \(K_{0}=0.71\)—sample 2.2: (**a**) Excess pore water pressure versus vertical strain characteristic, (**b**) excess pore water pressure characteristic versus number of cycles, (**c**) vertical strain characteristic versus number of cycles, (**d**) deviator stress–vertical strain relationship, and (**e**) the deviator stress–mean effective stress relationship (red color—last 10 cycles; arrow color—violet: Saturation phase, green: Consolidation phase, blue: Cyclic loading program). The axial strain, which was measured in this study, could be divided into two categories based on the plastic strain accumulation rate. The first one is steady exponential growth in which, the plastic strain increment decreases with each cycle. In this case, the soil might suffer extensive deformation due to accumulated plastic strains after numerous cycles. This type of response was observed in samples 2.2, 2.3, and 2.4. The second type of plastic strain development represents samples 2.1 and 2.5 where the extensive plastic strain was accumulated in the first phase of cyclic loading due to the imposed high value of the deviator stress. After a few thousands repetitions, the steady response of the cohesive soil was observed, which characterized the lower rate of plastic strain accumulation. Figure 7: Results of the cyclic triaxial test for sandy silty clay under a confining pressure of 139.7 kPa and under the \(K_{0}\) consolidation, initial void ratio \(\epsilon_{0}=0.379\), \(K_{0}=0.67\)—sample 2.3: (**a**) Excess pore water pressure versus vertical strain characteristic, (**b**) excess pore water pressure characteristic versus number of cycles, (**c**) vertical strain characteristic versus number of cycles, (**d**) deviator stress–vertical strain relationship, and (**e**) the deviator stress–mean effective stress relationship (red color—last 10 cycles; arrow color—violet: Saturation phase, green: Consolidation phase, blue: Cyclic loading program). The pore pressure response to cyclic loading was also influenced by the deviator stress value.