MEASUREMENTS OF SOIL DEFORMATION BY MEANS OF CONE PENETROMETER

PH. Reiffsteck, L. Thorel, C. Bacconnet, R. Gourves and H. C. van de Graaf

ABSTRACT: Measurement of the settlement of a cone submitted to incremental loading allows the determination of a modulus correlated to those obtained using laboratory tests or derived from other in situ tests. This test can be carried out with standard static penetrometer equipment. After stopping the penetration of a static penetrometer cone at a selected depth, an incremental loading test is carried out until the failure of the ground under the cone is observed. Stress strain relationships can be drawn from cone resistance and sleeve friction. In this manner, a modulus and a friction angle can be obtained. Thus the classical CPT log is enriched offering new possibilities. In this paper the development of the first prototype and measuring devices and the proposed testing procedure are presented. A comparison of laboratory and field tests and geotechnical centrifuge models shows the validity of the testing procedure and the chosen interpretation method. The results of site investigations carried out on French national experimental sites are also discussed and compared with high quality borehole expansion test and field measurement of shear wave velocity. These investigations have been carried out using this new testing method in combination with a semi-heavy static Piezocone penetrometer in order to check the potential use for geotechnical design. An attempt is made in this paper to validate the interpretation method of the results, which can be used for routine geotechnical engineering.

Key words : CPT, incremental loading test, in situ testing, modulus, penetrometer, stiffness, Piezocone (IGC: C3/D6)