Towards the development on new high capacity tensiometers capable of measuring soil matric suction beyond 3 MPa

Abstract

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.

High Capacity Tensiometers: performance and behaviours

“…As mentioned before, the AEV of the ceramic filter defines the upper limit of the measuring range of HCTs [11] and can be estimated from the size of the largest pore in the ceramic filter. Where, a smaller size of the largest pore corresponds to a greater AEV and, therefore, to a greater suction measuring range.…”

“…After cavitation, the level of saturation of the ceramic filter remains close to 100% and the application of high vacuum for the same period of time as during first saturation may cause water to freeze inside the ceramic filter and potentially result in the formation of cracks, endangering the ability of the HCT to measure suction. The resaturation procedure typically lasts for approximately 12hrs but, if the HCTs are placed in water immediately after cavitation as shown in [11] and [14], this time can be reduced to as little as 10 minutes for HCTs with small size reservoirs (<50 mm 3 ). If the HCT is left exposed to atmospheric pressure after cavitation, the resaturation time increases significantly.…”

A framework for estimating the matric suction in unsaturated soils using multiple artificial intelligence techniques

“…10,43,44 Remarkably, it facilitates matric suction measurement across a broad range, with the latest advancements enabling the measurement of matric suction up to 7 MPa. 45,46 Nevertheless, the challenge remains in reconciling the demands of equipment cost, efficiency, and accuracy within a single device. Consequently, most suction measurement techniques are widely used in academic research and have limited application in engineering practice.…”

“…The high‐capacity tensiometer stands out as an invaluable tool capable of directly and reliably measuring matric suction 10,43,44 . Remarkably, it facilitates matric suction measurement across a broad range, with the latest advancements enabling the measurement of matric suction up to 7 MPa 45,46 . Nevertheless, the challenge remains in reconciling the demands of equipment cost, efficiency, and accuracy within a single device.…”