New Tool for the Measurement of Soils' Shear Strength

Disturbance encountered when testing soft soils both in laboratory and in-situ conditions makes the determination of undrained shear strength, Su, very challenging. This paper introduces a new tool called "Cylindrical Shear Tool" (CST) to measure the undrained shear strength, Su, of soft soils. Description of this tool is given and the related shear test procedure is detailed. The proposed tool offers the advantage to avoid the disturbance of soft soils prior to the measurement of shear strength. From recorded measurements, and based on considerations of the existing shear tests, a specific method of determination of Su is proposed. Recorded results by the CST on a reconstituted Tunis soft clay revealed in fair agreement with those obtained from direct shear tests and from a triaxial test. Using the CST a series of tests was also performed from which the friction angle of the interface between the CST and a compacted sand is determined. First, characterization of the chosen quarry sand comprised identification tests, Proctor tests and the direct shear test (DST). Then follows the preparation of sand samples compacted, in Proctor molds, at the optimum modified and normal Proctor water contents. Those remolded sand specimens were subject to the CST tests for which the failure shear strength is captured. Then the method of determination of the sand specimens' friction angle is detailed.