A numerical interpretation of load tests on vibro-piles

The finite element interpretation is discussed of two load tests carried out on instrumented vibro-piles in a granular deposit. A first back analysis, aimed at assessing the improvement of the mechanical characteristics of soil induced by the vibratory construction process, highlights an apparent contradiction between the experimental variation of the axial load along the pile and the numerical results. This suggests introducing as a free variable, in addition to the elastic and shear strength parameters of the granular soil, also the increase of the nominal diameter of pile caused by vibrations. The second back analysis provides some insight into the variation of the diameter with depth and leads to an acceptable interpretation, from the engineering standpoint, of the load tests. On these bases a quantitative comparison is presented between the calculated load–settlement diagram of the vibro-pile and that of a “standard” pile constructed without vibrations in the same granular deposit.