## 3 Results and Discussion
### Isotropically and \(K_{0}\) Consolidated Samples Test Results
The cyclic triaxial test results in isotropic consolidation conditions where effective confining pressure was equal to 90 kPa present in Figure 3. The soil in this test had initially the void ratio equal to 0.345, which represents a more compacted sample in comparison to the previous test sample. The cyclic loading performed as well as in the previous test high pore pressure and permanent strain accumulation in the first cycle. Nevertheless, excess pore water pressure reached roughly 11 kPa (17 kPa in the previous test). Unlike the previous test the axial strain increment was greater than in the previous step (0.65% in test 1.2 and 0.16% in test 1.1). This difference was clearly caused by the difference between the initial void ratio and in the radial effective confining pressure. In the second stage of loading, the pore pressure rose in a greater amount than in the previous test. Figure 3: Results of the cyclic triaxial test for sandy silty clay under a confining pressure of 90 kPa and under the isotropic consolidation, initial void ratio \(e_{0}=0.345\)—sample 1.2: (**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 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, orange: First cycle of cyclic loading, blue: Cyclic loading program). Figure 4 presents test results for the soil sample under a confining pressure equal to 135 kPa and an initial void ratio \(e_{0}\) equal to 0.412. In the first cycle stage, the soil response was stiffer than in test 1.2 but pore pressure rose to 11.5 kPa, which was close to the response observed in test 1.2. The same conclusion could be formed, when the excess pore water pressure versus axial strain plots (Figures 3a and 4a) were compared. In the second stage of the soil response, the pore pressure rose as well as the axial strain in the same pattern. The permanent strain accumulation to \(\Delta u\) characteristics was almost linear in both cases,  
Figure 4: Results of the cyclic triaxial test for sandy silty clay under confining pressure of 135 kPa and under the isotropic consolidation, initial void ratio \(e_{0}=0.412\)—sample 1.3: (**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 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, orange: First cycle of cyclic loading, blue: Cyclic loading program). which means, that for the same amount of pore pressure increment, the same amount of accumulated plastic strain was observed. Nevertheless, the magnitude of this phenomenon was different in each stage. In both cases, the limit between the second and third stage of the soil response could not be distinguished. The excess pore water pressure level and its increment rise with initial effective confining pressure growth. The stress paths in all cases moved towards the deviator stress axis, which indicates undrained conditions. On Figures 5-9, results of the cyclic triaxial test in \(K_{0}\) consolidation conditions are presented. The soil response to cyclic loading differed when compared to previous tests. The excess pore water pressure in test 2.1 rose rapidly, which was accompanied by moderate axial strain accumulation. When the \(\Delta u\) increment started to decrease, the permanent axial strain began to develop. That process of the soil reaction to cyclic loading indicates that the pore pressure triggered plastic strain accumulation.