High capacity tensiometers (HCT) are the only type of sensors in existence that can measure soil matric suction directly and are regarded to be the most accurate and reliable technique for the study of suction evolution in unsaturated soils. The measurement with HCTs is possible due to their design, composed of ceramic filter with a specific air entry value (AEV), small water reservoir and pressure transducer. Where, the AEV of the ceramic filter, more precisely the largest pore size within the ceramic, plays the most important role in controlling the measuring range of HCTs. Specifically, decreasing the largest pore size within the ceramic results in an increase in the measuring range. In this work, a new development in HCTs is presented whereby the ceramic filter in HCTs was replaced from the typically used 1.5 MPa AEV ceramic filter with a new alumina ceramic filter with an estimated AEV of 3.5 MPa. To assess the performance of the new ceramic filter, similar designed HCTs were assembled with the Soil Moisture and the new alumina ceramic filters. Early results show that the maximum measuring matric suction range is beyond 3 MPa for HCTs assembled with the new alumina ceramic filter.

This paper presents the results and analysis of two cracking tests carried on specimens of silty clay. One specimen was prepared in slurry conditions without applying energy and the other specimen was compacted. They were dried in an environmental chamber at a constant temperature and relative humidity to study the effect of the initial consistency on the cracking behaviour. Weight measurements and photographic images taken at regular intervals documented the evolution of the specimens. THM models were then carried to capture the unsaturated flow in the porous medium due to evaporation, and its resulting shrinkage. All the numerical analyses were coupled, incorporating the effect of porosity change on the balance equations and the constitutive model. The transfer coefficients in the imposed drying boundary condition were based on calculations of aerodynamic surface resistances, taking into consideration the new fronts for evaporation created by the cracks. The constructed numerical model results capture the gravimetric water content loss and the occurring shrinkage for both specimen conditions.

The behaviour of soils undergoing deformation due to changes in water content can be described using Soil Shrinkage Curves (SSCs). The SSCs are normally influenced by several factors as the soil’s fabric, different compaction levels, residual void ratio, and the shrinkage limit. In this study, shrinkage curves at different compaction levels were obtained using both wax coating and image analysis as volumetric quantification methods. Both techniques returned consistent results. To fit the obtained experimental data, a single equation is proposed with fitting parameters pertaining to the physical characteristics of the soil samples used. The use of Mercury Intrusion Porosimetry (MIP) is also incorporated to further analyse the structure of the soils being studied. The effect of the drying path on the structure was more apparent in the size range of 100-2000 nm. The effects of compaction on soil structure and shrinkage behaviour were also discussed in the study. The presented work provides valuable insights on the effect of different compaction levels on the soil shrinkage behaviour.

High capacity tensiometers (HCT) allow the direct measurement of soil matric suction, and their major limitation is the occurrence of cavitation. In this paper HCT designs using different ceramic filters with varied air entry values (AEV), varied reservoir sizes, and different pressure transducers are assessed as to determine the impact that each component may have in the HCT performance. Moreover, the effectiveness of first saturation and resaturation processes is discussed in relation to the time required to prepare/recover HCTs. The results obtained with the different designs show that the measuring range is directly linked to the AEV of the ceramic filter and that the choice of materials used for the various components may affect the reliability of measurements in field installations if the thermal performance is not accounted for in the calibration procedure. The use of a 1hr high vacuum pre-stage followed by overnight water pressurisation at pressures equal or above the AEV of the ceramic filter was found to be the quickest process to fully saturate an HCT for the first time. While resaturation time for an HCT can be reduced to as little as a few minutes if the HCT is resaturated immediately after cavitation has occurred.