Pier Foundations

The primary flood-related concern at piers is the potential for scour. Two typical approaches are to design deep enough foundations to accommodate scour and to protect the streambed around the foundation to prevent or reduce the potential for scour.
Primary protection measures at piers include concrete riprap, stone protection, gabions, and grout-filled or sand/cement-filled bags. See FHWA IH-97-030, “Bridge Scour and Stream Instability Countermeasures” (
HEC-23
) for discussion on selection of measures.
The following should be considered the following to reduce the potential for pier scour:
  • Reduce numbers of piers by increasing span lengths, especially where you expect large debris loads.
  • Use bullet-nosed or circular-shaped piers.
  • Use drilled shaft foundations.
  • Align bents with flood flow to degree practicable.
  • Increase bridge length to reduce through-bridge velocities.
Where there is a chance of submergence, a superstructure that is as slender as possible with open rails and no curb should be used.
Because of uncertainties in scour predictions, use extreme conservatism in foundation design. In other words, deeper foundations may be cheaper. The capital costs of providing a foundation secure against scour are usually small when compared to the risk costs of scour-related failure.