## 5 Discussion
Concerning the relation between ICL and the natural sample compression line, the location of the in situ stress is at the left side of the intrinsic stress, and the curve cuts the ICL, a common feature for OC [12; 14; 39]. Nevertheless, the location of its final part it is not usual; it does converge with the ICL and does not even show a break in its slope. Only in [60] is it possible to find a similar trend, according to them, this occurs when bonding has not been destroyed by the imposed litostatic load. This may also be the explanation for the case of DC. Considering the sensitivity framework [16], it is possible to compare the mechanical behavior of natural and reconstituted clays, and therefore, to measure the strength caused by the geological history of each clay. Using the definition of the stress sensitivity, S\({}_{\sigma}\), as the ratio \(\sigma^{\prime}_{\text{vy}}/\sigma^{\prime}_{\text{vve}}\), with the results plotted in Figure 6D, a value of 2.2 was obtained for the DC. This is within the range measured in another clay from the Cenozoic Duero Basin, the Viso Clay [57], and similar to the lacustrine Todi and the Pietrafita Clay [12], but lower than the Corinth Marl, which was also studied by the same authors. Considering the geological characteristics of all the mentioned clays, in the case of the DC the role of carbonate is not intense enough to create an interparticle bonding. * On the strength of the COC From the study presented here, values from the unconfined compression tests (UCTs) are up to three times lower than those from the direct shear test (DST). When interpreting strength tests in OC, special care should be taken to ascertain whether the results have been affected by the presence of discontinuities. If so, the strain-stress curves are less sloped and have less marked peak values [3; 50; 61]. No signs were observed suggesting that discontinuities were affecting the tests, either in the laboratory when removing the samples tested, or in the morphology of the breaking curves. Thus, the obtained parameter Su represents situations in which isotropic failure occurs through the matrix. Considering the importance of the anisotropic behavior in the OC [15; 48; 49], larger samples should be used for further studies, because it is expected that in a higher volume, failure may be affected by these singular planes. After discarding the discontinuity effects on the UCT as an explanation for the low values in the UCT, the conclusion reached is that the DST reports more realistic values for Su than the UCT, as the latter clearly underestimates the strength of the clay. From a professional practice perspective, the Technical Construction Code [62] contemplates the possibility for OC to estimate settlement based on an elastic behavior, provided that the pressure transmitted is lower than its unconfined compression strength (q\({}_{\text{u}}\)). In this regard, the obtained consolidation curves for the clayey levels are the result of a mainly elastic behavior and seem to be the mechanism at least up to about 2000 kPa. Therefore, plastic settlement would be significant only for pressures above this value, outside the margins in which the construction takes place, and fulfilling the asseveration included in the Code. Regarding the mechanics of the strength, stiff behavior was observed in the clay levels of the DC, similarly to that reported in MOC of the Guadalquivir Blue Clay [3] or the London Clay [15]. Nevertheless, some differences are apparent considering the strain-stress curves, the brittleness index defined as \(\text{If}=(\tau_{\text{p}}-\tau_{\text{f}})/(\tau_{\text{p}})\), and the cementation loss (\(\text{CLf})=(\tau_{\text{p}}-\tau_{\text{pp}})/\left(\tau_{\text{p}}-\tau_{ \text{pf}}\right)\)[50]. For the former, the values are in the range 0.5-0.8, with an average of 0.6, and represent a measure of the total loss of strength.