A influência da compacidade das areias nas correlações entre os ensaios de cone e o SPT

Abstract

Correlations between the results from cone and SPT in sands are established in the present research for different sand densities. Such proposition is based on the experience obtained with the use of piezocone whose penetration in sands occurs commonly in drained condition. The SPT penetration, on the other hand, is much faster, occurring in a partially drained condition. The results confirm distinct correlations for different sand densities. The qc/NSPT ratio of 0,6MPa for sands, obtained from Danziger and Velloso (1986, 1995), for the whole data, is consistent with the value obtained in the present research if no distinction of density is made. If distinct density range is considered, the qc/NSPT ratio was found to be 1,1; 0,8; 0,6 and 0,5MPa, respectively for very loose, loose, medium and dense sands. Such results have repercussion on foundation design, as long as the most common methods applied in design make use of correlations between the CPT and SPT results. While the traditional correlations depend only on soil granulometry, the results presented in this research show that the relative density is of fundamental importance and must be also considered. In relation to the friction ratio, no tendency of variation with the relative density of sand has been observed, as expected, as long as both fs and qc are obtained from the cone. The results obtained with Palacios (1977) data, with liner removal, and also the comparison between the resistance mobilized during the SPT sampler penetration evaluated by Schmertmann (1979) and Aoki et al. (2004) show that sampler plugging in sand probably does not occur.