## 3 Results  
### State of the Material at Shallow Depths during the Year  
In situ conditions of the tested fissured clay are herein reported in terms of both matrix suction, s (Figure 5a) and degree of saturation, S\({}_{\text{r}}\) (Figure 5b) with reference to undisturbed samples taken at depths ranging between 0.7 and 1.6 m. The material was sampled from March 2012 to March 2013 in order to assess the impact of the soil-vegetation-atmosphere interaction on its state. In Figure 5a, filter paper measurements are referred to as FP, while ICL high-capacity tensiometer measurements are referred to as T. The results in the figure show that, at depths ranging between 0.7 and 1.6 m, the Paola Doce fissured clay presents matrix suctions roughly ranging between 27 and 1160 kPa during the year going from March 2012 to March 2013.  
Figure 4: Example of high-capacity tensiometer measurement.  
The state of the material at depths ranging between 0.7 and 1.6 m is very sensitive to weather variations, so the highest suction values, for instance, are not necessarily measured during the driest periods of the year, given that single, isolated rainfall events could easily affect general trends of suction variation [17]. Similarly, should rainfall events occur less frequently than expected during the wettest periods of the year, high suctions could also build up in seasons during which they are expected to be low. Despite the impact that short-term weather variations can have on the state of the outcropping soils, the data in Figure 5a seem to be in reasonable agreement with the general climatic features of the sampling periods. For example, except for a suction value measured in March 2012 with the tensiometers, the highest suctions, broadly varying in the range 195-680 kPa, were all recorded in August 2012. On the other hand, suction values lower than 195 kPa were measured in May 2012 and March 2013, with the lowest suction, of around 27 kPa, measured in 2013 at the end of winter. When looking at the data in Figure 5a, it is interesting to observe that at simi  
Figure 5: Water retention data of the Paola DOC fissured clay sampled at different depths and during different periods of the year: (**a**) matrix suction, measured with the filter paper technique, FP, and high-capacity tensiometers, T; (**b**) degree of saturation.  
lar depths, the suction values measured with the filter paper technique are consistently lower than those measured with the ICL high-capacity tensiometers. Comments on the differences between the two suction measurement techniques herein adopted are reported in the following.  
Similar to the matrix sutions in Figure 5a, also the degrees of saturation reported in Figure 5b show variations, with depth and time, that are generally consistent with the weather variations typically occurring during the year. For example, the lowest degrees of saturation were measured in August, with \(\mathrm{S_{r}}\) broadly ranging between 70% and 83% (except for a single value close to 90%). On the other hand, all the \(\mathrm{S_{r}}\) measurements conducted in March and May gave values roughly falling in the range 83-92%. It is interesting to observe that all the measured \(\mathrm{S_{r}}\) values are much lower than 100% even when associated with relatively low suctions. Following the framework proposed by [40], who provided an interpretation of the water retention behaviour of multi-porosity materials, the presence of \(\mathrm{S_{r}}\) close to 90%, even for suctions of a few kPa, could be mainly related to the desaturation of the fissures, as discussed more extensively in the next sections.