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Case Studies

A10 Viaduct and Bridge – Carregado, Portugal

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 Challenges

  • To recover the project completion timeframe
  • To triple the production rates versus the previous method with recoverable full casing
  • To ensure zero contamination in the nearby agricultural environmentally protected area

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.

Solutions/Benefits to client

Bearing in mind the sole purpose of increasing production, the method was changed to GEO’s synthetic slurry system (PolyMud-G3 System).With the new implemented method (drilling the piles using PolyMud), it was possible to recover the wasted time and greatly reduce costs with heavy equipment and personnel. In merely 4 months the remaining 500 piles were completed. Production tripled and deadlines were met.

With the change of method we confirmed that:

  • Daily production increased to 3 times faster than previous method.
  • Project schedule was recovered to meet the deadlines.
  • Wide overall reduction of costs with equipment and personnel.
  • Easiness and low cost slurry disposal.
  • Approval of the piles done with PolyMud.
  • Preserving of the environment.

All performed tests proved that the G3 System is environmentally safe and can be used in protected or sensitive areas without hazard of any sort to the environment.