Miniature T-Bar Penetrometer

The miniature T-bar penetrometer is used for in-flight measurement of the undrained shear strength of soft clays. On the basis of the measured tip resistance, the undrained shear strength is determined under the assumption of a plastic flow mechanism around the cylindrical T-shaped tool, according to the theoretical basis set by Randolph & Houlsby (1984).

Having a diameter of 7 mm and a length of 28 mm, the ETHZ miniature T-bar penetrometer is a modified version of the tool developed by Stewart & Randolph (1994). The load on the T-bar is measured with a load cell, installed exactly behind the T-shaped tip. For the activation of a full plastic flow mechanism, the T-bar has to penetrate several centimetres into the soil layer. The required penetration depends on the stiffness and strength of the investigated soil, being of the order of 2–4 times the diameter of the T-Bar according to experience.