Soil suction has been regarded by soil scientists as an aspect of increasing importance and has been used as an important source of information in agriculture since early last century. Its knowledge helps improve human actions not only in aspects relating to vegetation and agriculture, but also concerning slope stability. Increasingly sophisticated tensiometers have been designed to measure soil suction. This study describes the state of the art in the evolution of tensiometers, aside from the development of a tensiometer which measures stress values of at least 1.500 kPa. Various prototypes were developed. These devices differed in the characteristics of their components, but performed rather similarly in the results in the possible reading ranges in each case. The effects of the type of transducer, size of the water tank, dimensions and permeability to air of porous stone were analyzed and monitored, installed in lysimeters or together with other equipment such as equitensiometers and TDRs. Results showed that the prototype may be used in situ and in laboratory and is readily adaptable for use in an air oedometer or triaxial apparatus. The role of Van der Waals forces in the cavitation of the system was also discussed, explaining the procedures for shifting the point of cavitation to upper limits aiming at a reduction of possible gas nuclei in the system.
non-saturated soils; soil matrix potential; tensiometry
