Abstract
High capacity tensiometers (HCTs) are sensors capable of directly measuring tensile pore water pressure (suction) in soils. HCTs are typically composed of a casing that encapsulates a high air entry value ceramic filter, a water reservoir and a pressure sensing element. Since the creation of the first HCT by Ridley and Burland in 1993 at Imperial College London, HCTs have been almost exclusively built and used in academic research. The limited use in industrial applications can be explained by a lack of unsaturated soil mechanics knowledge among engineering practitioners but also by the technical difficulties associated to the direct measurement of tensile water pressures beyond the cavitation limit of -100kPa. In this paper, we present the recent design and manufacture of a new HCT at the Universite de Pau et des Pays de l’Adour (UPPA) in France. Different prototypes were tried by changing the main components of the device including the type of ceramic filter, pressure transducer and geometry of the external casing. In particular, two ceramic filters of distinct porosity, three pressure transducers with distinct materials/geometries and four casing designs were tested.
Highlights
High capacity tensiometers (HCT) can directly measure tensile pore water pressure in soils, which is an important variable for the hydro-mechanical characterization of these materials
HCTs are composed of a high air entry value (HAEV) ceramic filter, a water reservoir and a pressure transducer, all housed inside a casing made of stainless steel
A fully saturated HCT is exposed to the atmosphere so that the face of the ceramic filter is allowed to dry
Summary
High capacity tensiometers (HCT) can directly measure tensile pore water pressure (suction) in soils, which is an important variable for the hydro-mechanical characterization of these materials. HCTs are composed of a high air entry value (HAEV) ceramic filter, a water reservoir and a pressure transducer, all housed inside a casing made of stainless steel. Each of the above components can have a direct impact on the performance of HCTs. The ceramic filter has the strongest influence on the measuring range [10] because the highest measurable value of suction strongly depends on the air entry value of the ceramic, which in turn increases with decreasing size of the largest ceramic pore. The different prototypes make use of: a) two different ceramic filters with distinct air entry values of 700 kPa and 1500 kPa, respectively, b) three different pressure transducers, namely a flush diaphragm ceramic transducer, a cavity diaphragm ceramic transducer and a flush diaphragm stainless steel transducer and c) four different stainless steel casing dimensioned to accommodate the transducer and the ceramic as well as to create the water reservoir in four out of five prototypes.
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