## 3 Results and Discussion
### Isotropically and \(K_{0}\) Consolidated Samples Test Results
This was true since the excess pore pressure decreased the effective stress in the soil skeleton and therefore is weakening the soil contacts. During test 2.1 excess pore water pressure reached a maximum value equal to 35 kPa after around 2500 cycles of loading and then slowly decreased to 33 kPa after 3000 cycles. The excess pore water pressure remained after the previous event at a constant level and equaled 32 kPa up to 33 kPa. The soil response can be divided into two stages, the pre-maximal excess pore water pressure stage, where rapid pore pressure generation and permanent strain accumulation was observed, and the second stage--the post-maximal pore pressure stage where permanent axial strains suddenly stopped and pore pressure decreased to a constant level. It is clear that the decrease of pore pressure would result in an increase of effective mean stress and therefore would increase the soil stiffness and the permanent strain accumulation would rapidly decrease. The reason for this phenomenon is the critical soil state, which was achieved during the first part of cyclic loading. The soil accumulated 4% of axial permanent strain during the first 2500 cycles of loading. The pore water pressure development has led to soil failure. After the failure, the pore pressure dropped and therefore, the soil was able to sustain further loading. Furthermore, almost a constant high level of pore water pressure was observed, which was accompanied by a slight permanent strain accumulation. Figure 5e presents the abovementioned behavior. The stress paths moved towards the deviator stress axis and when the stress state reached the soil critical state, pore pressure decreased, and the stress path turned around. On Figure 6 triaxial test results on the \(K_{0}\) consolidated sandy silty clay sample is presented. The \(K_{0}\) stress state was equal to 0.71, which was close to the previous \(K_{0}\) stress state for sample 2.1, which was equal to 0.67. The initial void ratio in the case of sample 2.2 was around 0.07 greater than in the case of the 2.1 sample and was equal to 0.399. The type of loading in this study was a sin wave as in previous cases but it was performed in another manner. The soil was loaded with the deviator stress, which was oscillating around the point where the consolidation phase was terminated (\(q_{m}\) was on the deviator stress level reached after \(K_{0}\) consolidation). For example, the 2.1 test was performed in such a manner where the minimum deviator stress \(q_{min}\) was on the deviator stress level after consolidation. In the first cycles, negative excess pore water pressure was observed. After 10,000 cycles the excess pore pressure had raised to 30 kPa. The pore water pressure was building up with a decrease of its increment. This type of soil response caused almost no plastic strains (0.134% after 10,000 cycles). It seems that the type of loading has a great impact on the \(K_{0}\) consolidation samples response. The soil in which the negative pressure occurred would suffer much lesser plastic strains. This was a result of another pore pressure generation model. In the previous tests of isotropically consolidated samples, the pore pressure rose rapidly in the first few cycles, this was accompanied by plastic strain accumulation. Sample 2.1. also generated excess pore water pressure but was much faster than in the case of sample 2.2, which was the reason why the plastic strains were accumulated with a much slower rate. A similar response to cyclic loading can be observed in test 2.5 where the sample was consolidated to \(\sigma^{\prime}{}_{3}\) equal to 44.9 kPa. The soil was loaded with 13.3 kPa deviator stress amplitude and the excess plastic strain was observed. The pore pressure, in this case, had not reached maximal value, which indicates no failure in this test. The soil tended to stabilize its response to cyclic loading. The pore pressure after 5000 cycles increased at a slower rate and plastic strain as well accumulated with a decreasing rate.