The job owner formed by a private consortium and Brisa (Portuguese motorway authority), required the 3 special foundation contractors to conclude approximately 1000 piles to form the 11km viaduct, in a 12 months’ timeframe. The piles had 1500mm diameter and depths ranging from 42 to 60m. The environmental concerns were extremely high in this project, since it crosses an agricultural area. The job owner demanded the performance of lab analysis on the slurry itself, after application, mixing water and extracted drilling spoils.
The agreed initial execution method involved a recoverable casing to full depth. This method required the driving of 3 sets of welded casing using a vibrator. During the concrete pour, the recovering of the casing cut in 2 sets, required specialized welding personnel thus resulting in an expensive and inadequate method to meet the demanding timeframe. After 9 months of work, only 500 piles (half the project) were concluded. The soil conditions were also very demanding with the first 25m layer mostly composed by zero SPT mud, followed by 15 to 20m of fine to coarse sand preceding a layer of medium to coarse sand with abundant cobbles (30cm max. diameter). The setting of the piles was done 4 diameters into a rubble sandy layer.
With the change of method we confirmed that: