An Integrated High-Capacity Tensiometer for Measuring Water Retention Curves Continuously

The water retention curve (WRC), which characterizes the relationship between the water content and water pressure head, is an important hydraulic property of soils in the vadose zone. The application of a high-capacity tensiometer (HCT) to WRC measurement under a continuous drying process could significantly reduce the measurement duration compared with other conventional testing methods. However, the electric cable connecting the HCT to the data logger generally introduces errors in the soil mass measurement and, in turn, the water content results. In this study, an integrated HCT was designed, and a novel method was proposed to improve the measurement accuracy by using only one soil specimen. The integrated HCT comprised a digital millivoltmeter and a battery supplying constant voltage. The mass of this integrated HCT along with a soil specimen was recorded by a high-resolution electronic balance during continuous drying. Meanwhile, the water pressure head was also measured by the integrated HCT. Hence, the errors induced by the HCT cable and the separate soil specimens were avoided. It was demonstrated that the WRC of a compacted kaolin obtained using the integrated HCT was similar to that obtained using the recently proposed method in which two identical specimens are required. Because only one specimen was required, the newly developed HCT is a promising transducer for the WRC measurement of intact specimens under continuous drying.