Direct and Indirect Determination of Alluvial Sands Deformability

Abstract

The  foundation  piers  of  the  Coimbra  gated  dam  were  builted  through  sandy  alluvial material by means of diaphragm walls that  formed  a  caisson  whose  inside  sand  was  later  dredged for pouring concret. ln one of those caissons SPT and CPT tests were done before starting a careful manual excavation that allowed plate load tests to be performed in the undisturbed sand at many different leveis. Determination of "in situ" volumetric wheight and collection of integral samples was also done. The water level was maintened, by pumping, at the same elevation of the excavation inside the shaft.

Laboratory one-dimensional compression tests at different initial void ratios were executed with the sands recovered at the levels of the tests.

The results obtained allowed interesting correlations between penetration and deformability and to verify some known relationships between SPT and CPT test results. Grain size influence on that correlations was also analised.

Plate load tests and one-dimensional compression tests at different initial void ratios gave quantitative indications about the correlation between CPT and deformability according the type of sands and "in situ" void ratio.