This program is a result of the hard work of several foundation engineers, over one thousand pile load tests results and many, many successful projects. It started long ago by the late Professor Velloso and Professor Aoki at Franki Pile company, where they started in the mid 60’s. Indeed, since the early 30’s Franki Pile engineers realised the advantage of correlating index N from SPT to pile bearing capacity in order to predict pile depth. The advantages of these correlations are obvious: no need to estimate soil properties, just soil type and N. Even, the water level depth is irrelevant, since its effect is included in the given N value.
Franki pile engineers Dr Dirceu Velloso and Dr Nelson Aoki assembled a large pile test database over the years. They eventually published their AV (Aoki-Velloso) correlations in 1975. Thanks to their efforts, thousands of deep foundations were properly designed.
Dr Velloso and Dr Aoki left Franki in the 80’s to become, respectively, Professors of soil mechanics In Rio de Janeiro and São Carlos, Brazil. Their work was, then, taken over at Franki by Mr Paulo F Monteiro, who introduced new pile types, not covered by the previous work and increased Franki database with new pile types. This work became the PFM correlations, first published in 2000.
At the 12th International Conference of Soil Mechanics and Foundation Engineering held in Rio de Janeiro, a meeting on the Drivability of Piles took place. It was an excellent opportunity to demonstrate the accuracy and worldwide coverage of AV’s correlations used in this program.
Professor Kusakabe, who chaired the session, presented the results of class A predictions made by participants from Japan, China and Europe and Brazil of six piles driven in Japan which were loaded tested. The participants received SPT’s, pile type and length and had to forecast the pile load test results. Aoki (1989)’s predictions were by far the best. Prof Kusakabe (1989), on behalf of the committee, wrote, then:
It is then very clear that the AV SPT’s correlations can be used anywhere.
A similar work, but based on a completely new database was assembled by the foundation consultants Mr Luciano Décourt and L Quaresma (DQ correlations). They simplified the many soil types required AV and PFM correlations, included residual soil types and published their results in 1978. More recently, researchers at the University of Rio Grande do Sul (Lobo et al, 2005 and 2009), also assembled a large database with nearly 300 pile load tests and proposed a new set of correlations taking into account energy corrections for the SPT test.
All these methods include many soil types from sedimentary to residual soils. However they cannot be better than the database they represent. Which, then, is the best method ? There is no better method, the right answer is when different correlations point out in the same direction and give the same result. That’s why the user of these correlations is encourage to try at least two of them. If they point out to the same result, that’s should be the right answer.