## 4 Discussion and Conclusions  
The present paper reported and discussed data that allowed characterising the hydro-mechanical behaviour of a natural unsaturated fissured clay, i.e., the Paola D once clay outcropping at Pisciolo (with specific reference to the soil sampled between 0.7 and 1.6 m depth, i.e., the material forming the clayey slope cover). The micro- to meso-structural features of the material were first analysed, also based on Scanning Electron Microscope (SEM) micrographs taken on an undisturbed sample extracted at 1.4 m depth. The SEM images allowed estimating the opening of the fissures (broadly in the range 10-100 \(\upmu\)m) that split the material in clay elements (most of them from a few to several millimetres in size), confirming that the Paola D once clay exhibits at least a double-porosity, represented by the \"intra-element\" and the \"inter-element\" pores (i.e., the fissures). Water retention data of the Paola D once fissured clay at Pisciolo were also presented, showing how the state of the material located at 0.7 to 1.6 m depth changes, during the year, as a result of the soil-vegetation-atmosphere interaction. Despite the impact that short-term weather variations can have on the state of the outcropping soils, both matrix suctions and degrees of saturation seemed to be in reasonable agreement with the general climatic features of the sampling periods (i.e., March 2012-March 2013). For example, almost all the highest suction values (>195 kPa) were recorded in August 2012, while the lowest suction (\(\approx\)27 kPa) was measured in 2013 at the end of winter. Similarly, the lowest degrees of saturation were measured in August (generally S\({}_{\mathrm{r}}\approx\) 70-83%), while S\({}_{\mathrm{r}}\approx\) 83-92% was measured in March and May. Water retention data were collected not only on undisturbed samples (i.e., with reference to in situ conditions) but also after preparing specimens that were subjected to drying paths. All these data were interpreted based on the preliminary micro- to meso-structural analysis presented, trying to make a link between the water retention behaviour exhibited by the Pisciolo clay and its fissured structure. Based on the data currently available, it is believed that the desaturation of the material takes place at very low suctions as a consequence of the water drained out of the fissures (i.e., the \"inter-element pores\"). This can be interpreted as the \"first\" air-entry value (AEV) of the material (i.e., the \"inter-element AEV\"), followed by a \"second\" air-entry value, which is associated with the start of major S\({}_{\mathrm{r}}\) reductions, identified as the stage at which air enters the intra-element pores (i.e., the \"intra-element AEV\"). For most of the samples subjected to a prolonged drying that reached high suction values, the \"intra-element AEV\" was observed for s = 1000-2000 kPa, in conjunction with a major reduction in void ratio (i.e., a \"volumetric collapse\"). The water retention data presented in this paper refer to suction measurements performed by means of two different methods, i.e., high-capacity tensiometers and the filter paper technique. A comparison between the results obtained with these two methods was also presented, showing how, for the tested material, the high-capacity tensiometers were recording suction values consistently higher than those measured with the filter paper technique. Even though more extensive investigations are necessary in order to fully understand the reasons behind these differences, a tentative explanation of these findings was provided by considering the fissured structure of the Paola Doce clay outcropping at Pisciolo, potentially allowing the elements between the fissures to have a \"near-independent\" hydro-mechanical response during drying. This would imply that the tensiometer tips would be more likely to measure \"local\" suctions, while the filter paper disks would be able to measure more representative average suctions, being in contact with a bigger area of the specimen.