19 June 2001
TR-5: REPAIRING TIMBER PILES WITH CONCRETE ENCASEMENT
Problem: Approximately 10 to 50 percent of the cross-sectional area has been
lost as a result of marine borer attack.
Description of Repairs: Clean the timber pile thoroughly from below the mudline
to above MHW. Two types of forms are available:
Split fiberboard forms
After piles have been thoroughly cleaned, place a 15- by 15-cm (6- by 6-inch)
reinforcing mesh around the pile, using spacers to maintain clearance between
pile, reinforcing, and fabric form. The fabric form should be placed around the
For the flexible form, the zipper should be closed, and the form secured to the
pile at top and bottom with mechanical fasteners (see Figure 6-5).
For the fiberboard form, straps are installed and secured every 30 cm (1 foot).
Maintain a minimum of 40 mm (1 9/16 inch) spacing between pile and reinforcing
and between reinforcing and form (see Figure 6-5).
The space between pile and form is then filled to overflowing with concrete grout.
Use a tube or hose extended to the lowest point of the form.
The form is left in place and the base is backfilled to above the concrete.
Application: This method can be used as a repair or as protection against
marine borer attack and abrasion, and may be more expensive than replacing
one or more timber piles. Economics will dictate decision.
Future Inspection Requirement: Increased inspections may be required to
detect signs of ripped fabric forms, unzipped or locked form seams, or abrasion
and failure of concrete encasement.