Use of the Sharp Cone Test for In Situ Determination of Undrained Shear Strength of Clay

A recently developed in-situ testing method, called "The Sharp Cone Test" consists in pushing a low-angle truncated cone with 2 degrees taper into a smaller diameter prebored pilot hole. As the cone descends, it causes a continuous enlargement of the pilot hole, which, with a proper instrumentation, can be translated into a relationship between radial pressure and radial (or shear) strain, similarly as in a pressuremeter test. A first, preboring version of the sharp cone with three lateral pressure sensors, was tested in the field five years ago, and yielded positive results (Ladanyi et al. 1995). The present paper describes the use in the field of an improved, self-boring version of this instrument with four total-pressure transducers mounted on its lateral surface at different distances from its lower end. The new probe is able to furnish continuously four points of the pressure-expansion curve, which can be translated into a stress-strain relationship, using conventional pressuremeter data processing procedure. During 1998, the new instrument was tested in a thick layer of saturated clay at a site near Montréal. A comparison of the results with those obtained at the same site by some other types of tests, such as self-boring pressuremeter test and static cone test, was encouraging. The new testing method represents in fact a continuous and automated version of the pressuremeter test.