Volume 35, N. 1, January-April 2012 | DOWNLOAD PDF(38 downloads)
Abstract
Correlations between CPT and SPT in sands are presented in this paper for different sand densities. Such proposition is based on the experience obtained with the use of piezocone whose penetration in sands occurs commonly under drained condition. The SPT penetration, on the other hand, is much faster, occurring under a partially drained condition. Due to the high loading velocities, much higher than that of the CPT, the SPT test can generate positive excess pore pressures in loose sands and negative excess pore pressures in dense sands. In this way, the N value may be higher than if the test were carried out in a drained condition, for dense sands, and smaller for loose sands. The same does not occur for the qc value of CPT. So, the trend would be of greater qc/N60 ratio for loose sands than for dense sands with the same grain size distribution. The results confirm distinct correlations for different sand densities. The qc/N60 ratio of 0.5 MPa/blows/0.30 m for sands, obtained from Danziger & Velloso (1995) regardless of the sand density, is consistent with the value obtained in the present research for the whole data, if no distinction of density is made. For distinct sand densities, the qc/N60 ratio was found to be 0.7; 0.5; and 0.4 MPa/blows/0.30 m, respectively for loose, medium and dense sands. While most of the correlations in the literature depend only on grain size, the results presented in this paper show that the sand density is of fundamental importance and should also be considered to interpret CPT and SPT correlations.
