Transportation Curriculum Coordination Council

Piles

There are a variety of pile types used in construction. Generally, the designer selects the type of pile to be used for the foundation system based upon several factors:

1. The loads the foundation system must carry.
2. The type of structure being built.
3. The geologic conditions found on the site. (For instance, how long do the piles need to be to reach the material needed to support the structure?)
4. Special design needs, such as resistance to ship impact for bridge piles.
5. Specifications or Standards relating to construction.

Driven piles consist of two basic systems- Displacement piles and Low (commonly referred to as non) Displacement piles.

Displacement piles are piles that actually displace the material they are driven into. For instance, if you push your finger down into sand, you actually move aside or displace, virtually all of the sand. Your finger now occupies the area that had been occupied by sand.

Low (Non) Displacement piles are piles that displace very little of the material they are driven into. Insert a knife blade into the sand. It goes in a little easier than your finger because it is not attempting to displace nearly as much material as your finger was. Although these piles actually do displace some material, the volume or amount displaced is substantially less than that of displacement piles.

Pile foundations develop their load carrying capacity in two ways. One by coming to rest on material hard enough to carry the loads to be imposed, commonly called end-bearing. Secondly through the ability of the materials to grab onto the sides of the piles and hold them, commonly called friction. In many instances, designers rely on a combination of both of these to support the pile.

Common Pile Types Used on FDOT Projects

• Prestressed Square Concrete Piles
  • Prestressed square concrete piles are displacement piles and the most common in Florida
  • Typically used where limestone or dense stratum is <125'
  • Used in corrosive environments
  • Used as friction piles, end bearing piles, and combination of both
  • Voided piles are made to reduce pile weight
  • Voided piles with solid ends provide some protection during driving
  • Driven as a group can sometimes densify soils in the immediate area

  

• Steel Piles, both Pipe Piles and "H" Piles

  Pipe Piles

  • Open end often start as non displacement piles, but as they plug, become displacement piles
  • Closed end are displacement piles
  • Typically used where pile lengths over 125' are needed or extremely variable subsurface conditions exist
  • Higher lateral capacity than H-Piles
  • Ease of splicing is big advantage
  • Non displacement piles are often used where a large number of piles are needed in a small area, such asunder a Bascule bridge pier
    
    

  H Piles

  • Are non-displacement piles
  • Not as common as concrete piles in Florida
  • Typically used where pile lengths over 125' are needed or extremely variable subsurface conditions exist
  • Ease of splicing is big advantage
  • Non displacement piles are often used where a large number of piles are needed in a small area, such asunder a Bascule bridge pier

  

• Cylinder Piles, (hollow concrete piles)
  • The least common of the typical piles
  • Are hollow prestressed concrete pipes manufactured to project needs
  • Used when project is accessible by barge
  • Used in corrosive environments
  • Can be used as both end-bearing and friction piles
  • Is considered displacement pile, that following installation can be filled with concrete or other materials
  • Is very heavy and requires larger than typical barges, cranes and driving equipment

  

• Timber Piles
  • Typically 8" tip and 12" butt diameters
  • Common lengths 15' to 50'
  • Typically made from pressure treated southern pine or Douglas fir woods
  • FDOT project use includes temporary structures, docking and fender systems, detour bridges and Bailey bridges

  

Bent/Pier

Piles are typically driven in groups and finished as either bents or piers as discussed below.

In a bent, the piles rise above the ground surface to a specified elevation. At this elevation, the piles are tied together with a bent cap.

In a pier, the pile tops generally are at or below existing grade. At this elevation, the piles are tied together with a pile cap (footing). Then a column is constructed from the pile cap up to the required beam seat elevation, where it is finished for connection to the structure.

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