## 4 Discussion
The values logged by the FP method (Figure 6) are believed to be accurate enough to be used as a benchmark for the evaluation of the accuracy of the TEROS 21 measurements. In this perspective, it can be concluded that for the low water content of the soil specimen (high soil suction), the wet TEROS 21 seems to be more effective in logging accurate suction values, i.e., the wet TEROS 21 measurement is closer to the FP datum. Instead, when measuring the suction for a higher water content in the soil specimens (low soil suction), the dry TEROS 21 appears to yield more accurate readings. However, it is also worth mentioning that the FP method is believed to be less reliable when measuring low suction values. As such, it can be stated that the better accuracy of the dry TEROS 21 at a low suction level may not be validated. Temperature variations affect suction measurements, influencing the accuracy of suction readings [46]. Additionally, the initial water content affects the temperature response, with a higher water content leading to more significant temperature variations. Temperature stabilization is indicative of approaching equilibrium, suggesting that a stable temperature is a sign of the system nearing equilibrium (Figure 4). The temperature variations during the suction measurements in the second test (Figure 6) further complicated the process, particularly between 60 and 180 h after the test began. These variations are likely linked to the laboratory conditions and the thermal response of the sensors, as observed in the comparison between the thermocouple and the TEROS 21 sensor. The temperature variations correlate with the suction changes, indicating coupled thermal-hydraulic behavior, as previously reported [40; 45]. The water retention data presented in this study were obtained using multiple measurement methods, including the TEROS 21 sensor, an HTC, and the FP technique. From the data in Figure 7, a consistent agreement between the suction measured using the FP approach and the suction measured by the water potential sensor can be recognized, especially for a suction range between 300 kPa and 2000 kPa. However, a comparison of the monitored data obtained from these methods demonstrated that, for the tested material, the FP technique recorded higher suction values than the TEROS 21 sensor for water content exceeding 30%. The differences in the test results between the two methods (i.e., TEROS 21 and FP) at a low water content can be attributed to some uncertainties inherent in both techniques. As for the TEROS 21, a potential factor affecting the reliability of the water potential measurements at high suction levels is the steep slope of the WRC of the probe's porous stones. At a low water content, even a slight change in the water content leads to a substantial variation in the suction values, given that suction is represented on a logarithmic scale. Indeed, the WRC of the porous stones became nearly horizontal for suction values between 1000 and 10,000 kPa. Similarly, the FP technique is also affected by potential sources of error in measuring the suction level. At high water contents, the FP is known to be less effective in measuring low suctions (i.e., \(<\)100 kPa) [28]. Moreover, a delay in weighing the FP after the moisture equilibration may lead to moisture changes, thereby reducing the measurement accuracy, as already recognized by [PERSON] et al. [47]. Such inaccuracies may reach even some orders of magnitude [47]. Additionally, a slight discrepancy was observed between the suction values obtained using the FP technique in test 2 and those from the undisturbed sample in test 3 (Figure 7). This variation may be attributed to differences in the micro- to mesostructural features of the fissured clay [48], which may have resulted in different void ratios [8; 26; 48] and, consequently, led to distinct HM responses during drying.