## 3 Results and Discussion
### Oedometer Test Results  
Figure 4 shows the results obtained from the oedometer test, namely the displacements and the generated CH4 gas over the time of the experiment. From Figure 4, three distinctive phases can be distinguished. The first phase is related to the increase in the vertical stress while the specimen was in the dry state of the material. Such a condition reflects the current operational stage of the Mariscina landfill. The second phase denotes the beginning of the post-closure landfill state when the wetting process is going to be initiated. The initial wetting point is denoted in Figure 4 with a white circle and subsequent wetting points are denoted with white squares. Clearly, immediately after the wetting process was initiated, a significant amount of settlement took place. It is also interesting to observe that subsequent wetting did not produce additional settlement caused by wetting. Therefore, settlement that took place approximately 24 h after the initial wetting process can mostly be attributed to mechanical creep and, to a minor extent, to aerobic decomposition. The third phase denotes the anaerobic decomposition phase, which has a high methane yield rate. Figure 4 reveals that in the first operational phase of the Mariscina landfill, only 50% of the total settlement will occur. The majority of the remaining 50% will take place in the second phase when the wetting process will be initiated. A minor degree of additional settlement will occur in the third phase due to the anaerobic decomposition of the organic content. Figure 5 presents the coupled experimental results obtained with air pycnometer and oedometer tests. The lower half of Figure 5 shows the results obtained with the air pycnometer, whereas the upper half of Figure 5 presents the results obtained with the oedometer device. The results obtained with the oedometer device in Figure 5 are denoted with the following symbols: the black triangles represent the dry state of the material and the densification caused by the vertical load; the red triangle corresponds to the wet state of the material and the compaction caused by the wetting procedure, mechanical  
Figure 4: Displacements and methane yield measured in the oedometer test. creep, and aerobic decomposition; and the blue triangle depicts the \"compaction\" caused by the anaerobic decomposition process. For comparison, the theoretical curve, obtained with Equation (3) at a constant solid particle density set to 1820 kg/m\({}^{3}\), is also presented in Figure 5. In addition, Figure 5 also shows black lines, which represent the void ratio boundaries attained with Equation (3) at a solid particle density of 1820 kg/m\({}^{3}\) \(\pm\) SD of 190 kg/m\({}^{3}\). Once again, the particular air pycnometer specimens, which measured the solid particle density, lie close to 1820 kg/m\({}^{3}\), strongly resembling the theoretical curve. Obviously, the oedometer data also resemble the theoretical curve because the initial void ratio of the tested specimen was also calculated at a mean solid particle density of 1820 kg/m\({}^{3}\). Consequently, subsequent changes in the void ratio, caused by the vertical load, wetting process, and mechanical creep, also show a good fit with the theoretical curve. However, due to the strong heterogenous nature of the tested waste material and the strong variability in the solid particle density, it is more realistic to expect that the void ratio varies within the limits denoted with black lines. From Figure 5, it can be seen that only one oedometer point (denoted with a blue triangle) significantly deviated from the theoretical curve. This is the point where the decomposition process ended. The observed deviation was caused by the decomposition process, which increased the solid particle density and simultaneously decreased the dry density of the tested specimen.