A tensiometer for measuring hydraulic potentials on surfaces of porous rock

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Abstract
A laboratory method for obtaining tensiometer measurements on surfaces of porous rock and soil is presented. The construction and performance of two versions of the “surface tensiometer,” developed for determining near‐zero values of matric potential on rock surfaces, are described. Laboratory surface tensiometer measurements were made on a natural fracture surface of a Bishop Tuff block equilibrated with a water table boundary set at elevations ranging from −51 to +25 mm relative to the tensiometers. All equilibrium readings were within 10 Pa of ideal values, and most were within 5 Pa. Response times associated with this instrument‐rock system were in qualitative agreement with the matric potential–dependent hydraulic properties of the rock block.