## 3 Results and Discussion
### Compressibility  
The behavior of sedimentary and residual soils differs in several aspects, and this difference can usually be observed analyzing the void ratio-pressure plots both as linear and semi-logarithmic representations [29]. Furthermore, in sedimentary soils, the preconsolidation pressure determines the reaction of the soil to a variation of stress, whereas vertical yield pressure governs the behavior of residual soils. Both the significance and the physical meaning of these two stresses are different. The preconsolidation pressure can be modified by partial soil erosion over time after deposition or by height variation of the water table. An increase in the vertical effective stress caused by either reason generates the compression of the soil and the increase in its constrained modulus. In contrast, the yield stress is related significantly to the rock's weathering in a geological context rather than the depth where the samples were collected [30]. For this reason, consolidation is usually not studied in the same way in residual and sedimentary soils. Although in both cases the  
Figure 9: CBR test results. (**a**) stress against penetration for oven-dried samples, (**b**) stress against penetration for undisturbed samples, and (**c**) California Bearing Ratio against dry unit weight for both samples. void ratio-pressure plot is analyzed, for sedimentary soils it is typically represented with the effective pressure axis in a logarithmic scale, whereas for residual soils, a linear scale is used. Three undisturbed and three oven-dried specimens, all 50 mm in diameter, were tested in the oedometer for this investigation. The oedometer curves obtained in the testing campaign for undisturbed and oven-dried samples in a linear form are shown in Figure 9(a),b, respectively, while Figure 9(c),d shows them in log form. The results plotted in a linear form do not show a clear and pronounced gradient change at a particular stress level, as reported in the literature [29]. The analyses of the traditional void ratio against vertical effective pressure in log scale show a preconsolidation pressure between 200 and 300 kPa (Figure 9(c),d). Over-dried specimens show vertical  
Figure 10: Odometer test results: (**a**) undisturbed samples in linear form, (**b**) oven-dried samples in linear form, (**c**) undisturbed samples in vertical effective stress logarithmic form, (**d**) oven-dried samples in logarithmic form. yield stress that depends on the energy used to remold the sample rather than a natural preconsolidation pressure. Independent of the logarithmic or linear form of analyses, the initial void ratios determined in undisturbed samples were between 2.57 and 2.44 (Figure 10c), while the oven-dried samples were in the range between 2.25 and 1.97 (Figure 10d). Therefore, the initial void ratio of undisturbed samples can be considered high in comparison with most sedimentary soils. For foundations supported in residual soils, it is recommended to assess the consolidation settlement with the coefficient of compressibility (m\({}_{\text{v}}\)) instead of compression (C\({}_{\text{c}}\)) and swell (C\({}_{\text{s}}\)) indexes [29]. The mean coefficient of compressibility determined for undisturbed samples within the vertical effective stress range of 25-400 kPa was 6.42\(\cdot 10^{-3}\) kPa\({}^{-1}\), whereas for oven-dried specimens in the same effective vertical stress, an average m\({}_{\text{v}}\) of 9.7\(\cdot 10^{-3}\) kPa\({}^{-1}\) was obtained. The compressibility coefficient determined on residual soils and alloponic soils reported in the literature and performed within the same stress range as in this research range from 6\(\cdot 10^{-3}\) and 2.5\(\cdot 10^{-4}\) kPa\({}^{-1}\)[29]. In oedometer tests, a minimum number of settlement readings per loading pressure are required to determine an accurate coefficient of consolidation (c\({}_{\text{v}}\)). If the number of readings in the straight part of the curve is less than three, the coefficient of consolidation is inaccurate.