Guide To Seawalls

MAJOR TYPES OF SEAWALL FAILURE

ANCHOR FAILURE

Causes:

Age
Prolonged exposure to saltwater where corrosion has deteriorated the anchor rod and fasteners to a point when exposed to excess loading from behind possible failure of the wall can occur.

WARNING SIGNS THAT INDICATE POSSIBLE FAILURE:

  • Outward Movement
  • Misalignment of the seawall
  • Deterioration of the anchor rod

NOTE:  To fully determine that an existing anchor rod is not reliable, the rod needs to be exposed completely from the seawall cap to the anchor block.  Due to the amount of excavating required, this is not economically feasible.

SEAWALL CAP FAILURE

Causes:

Age
Prolonged exposure to saltwater where corrosion has caused the reinforcing steel in the seawall cap to corrode and expand causing cracks to develop. As the steel continues to corrode and expand, portions of the cap will break off, thus weakening the cap, leading to failure of the seawall.

WARNING SIGNS THAT INDICATE POSSIBLE FAILURE:

  • Outward Movement
  • Misalignment of the seawall
  • Horizontal cracks in face and top of the existing seawall cap
  • Are pieces of the cap missing or signs where sections of the cap are about to fall off.

NOTE:  Hairline cracks perpendicular to the seawall cap are in most cases normal shrinkage cracks.

SEAWALL SHEET PILE FAILURE

Causes:

Age
Loss of berm in front of the seawall causing the toe of the seawall to move outward at the bottom.

Excess loading from behind causing horizontal cracks to develop in the seawall sheet piles, exposing the reinforcing steel in the sheet piles to saltwater.  Prolonged exposure to the harsh elements weakens the sheet piles, which will lead to failure of the seawall.

WARNING SIGNS THAT INDICATE POSSIBLE FAILURE:

  • Misalignment of the seawall
  • Outward movement of the seawall sheet piles (normally at barnacle line)
  • Horizontal cracking in face of the seawall sheet piles (normally located at bottom of seawall cap or mid point of the seawall).

NOTE:  It may be necessary to remove some of the barnacles from face of the sheet piles to expose the cracks.

Settling of fill from behind the seawall due to outward movement of the sheet piles.

CAN ANYTHING BE DONE TO PREVENT A FAILURE?

Yes, but deciding what to do can be very complicated. To make matters worse, some individuals, and some marine contractors professing to be experts have little or no experience in understanding the causes of premature seawall failure. In some cases, they give poor advice on repairing only the obvious problems. The more significant problems are ignored, leaving the seawall prone to failure and more expense for the homeowner. An easy guide to detect common signs of seawall problems is included in this manual as a visual inspection questionnaire.

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