Tensiocone: A cone penetrometer with the facility to measure negative pore-water pressure

CPT sounding initially passes through the vadose zone, that is the zone above the phreatic surface where pore-water pressure is negative and degree of saturation is usually lower than unity. Negative pore-water pressure (suction) significantly affects tip resistance and sleeve friction and lack of knowledge of soil suction in this zone makes CPT data difficult if not impossible to interpret. For the case of Piezocone Cone Penetration Test (CPTU), crossing the vadose zone also exposes the cone tip porous filter to desaturation jeop-ardising the measurement of positive pore-water pressure once the cone penetrates the saturated zone below the phreatic surface. This paper presents the concept of the Tensiocone, a cone penetrometer with the facility to measure pore-water pressure in both negative and positive range. A first prototype was tested in the laboratory and in the field to investigate one of the major challenges in Tensiocone measurement, that is whether adequate contact can be established between the ground and the tensiometer porous filter during penetration.