## 3 Results
### Comparison between Filter Paper and High-Capacity Tensiometer Measurement Techniques  
One specimen, named \"Specimen 3\", has been tested with both the filter paper technique and the ICL high-capacity tensiometers at each stage of the drying process in order to assess the impact of the measurement technique on the suction value determined. The data of Specim 3 are reported in terms of matrix suction, s, against degree of saturation, Sr (Figure 7a), void ratio, e (Figure 7b), and volumetric water content, \(\vartheta_{\text{w}}\) (Figure 7c). As observed for the data in Figure 5a, the high-capacity tensiometer measurements performed on Specim 3 result in higher suction values than those obtained with the filter paper technique (Figure 7). This finding is in contrast with what has been reported by [45], who justified their results by making reference to the high salt concentration that characterised the pore water of the tested material. In fact, high salt concentrations are associated with high osmotic suctions, the latter potentially measured if there is no good filter paper contact or when Sr reduces significantly.  
Further investigations are required in order to make a more comprehensive comparison between high-capacity tensiometer and filter paper measurement techniques. As part of the study herein summarised, in order to increase the reliability of the suction values determined with the tensiometers, the measurements were often repeated by putting a different tensiometer in contact with the second base of the specimen tested. For example, the highest suction value reported in Figure 7 corresponds to an average value obtained from measurements performed on the two bases of Specim 3.  
In order to better understand the extent to which the average value of the tensiometer measurements can be considered representative, it is interesting to observe in detail the results of each measurement conducted on each base, for instance with reference to the final drying stage of Specim 3 (reported in Figure 8). The two measurements conducted on the two bases (named Base 1 and Base 2 in Figure 8) are significantly different, and this difference was also confirmed by repeating the measurements with different tensiometers (referred to as Measurements 1 and 2, for each Base, in Figure 8).  
Figure 7: Water retention data of a specimen (tested with both the filter paper technique, FP, and high-capacity tensiometers, T) reported in terms of matrix suction against: (**a**) degree of saturation; (**b**) void ratio; (**c**) volumetric water content.  
A tentative explanation of these findings could be provided by considering the meso-structural features of the material, potentially allowing the clay elements between the fissures to have a \"near-independent\" hydro-mechanical response during drying. This would mean that the tensiometer tips would be more likely to measure \"local\" sections, which is not necessarily representative of the average value of the whole specimen. On the other hand, the filter paper disks would be able to measure more representative average suctions, being in contact with a bigger area of the specimen. Such an interpretation would be more sensible at lower degrees of saturation, such as the one characterising Specim 3 at the end of the final drying stage (Figure 7a). As a matter of fact, a major desaturation of the fissures could reduce significantly the hydraulic connection between the clay elements, allowing them to behave like \"specimens in the specimen\".