BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

The surface decay and deterioration is considered minor in 75% of the piles, moderate in 15% of
piles and significant in 10% of the piles.
The piles throughout the bridge also contain checks and splits of adequate width and depth to
penetrate the outer portion of the piles that contains the preservative treatment. This permits
moisture and fungal spores to gain access to the interior of the pile where there is no preservative
treatment, which creates conditions conducive for development of internal fungal decay. The
checks and splits are considered minor in 75% of the piles, moderate in 15% of piles and severe
in 10% of the piles. Two of the piles (one in Bent 4A and one in Bent 6) exhibit extensive splits
at the top of the piles where the piles connect to the cap beams.
In general, the tops of the piles are sound. However, there is no evidence that the cut ends of the
top of the piles were field treated with preservative or sealed either during the original
construction, widening or reconstruction. As such, the cut ends provide opportunities for
moisture absorption and decay at the tops of the piles.
There is evidence of active marine borer attack in approximately one-third of the piles
throughout the bridge. In addition to the twelve (12) piles wrapped in plastic with previously
identified marine borer attack, there are six (6) piles with marine borer attack extending from the
mudline through the tidal zone, nineteen (19) piles within the tidal zone and four (4) piles near
the mudline only. The most severe deterioration has occurred to a pile in Bent 8, which
reportedly includes approximately 80% loss in cross section to the pile. The marine borer attack
is primarily from teredo worms that consume the interior of the pile where there are no chemical
preservatives. However, there is evidence that limnoria (gribble) has also attacked the exterior
surface of the timber. The teredo worms have typically bypassed the chemical preservatives in
the surface of the piles and have accessed the interior of the piles through bolt holes in the piles.
A number of the holes that were previously used for bolting timber bracing members to the piles,
but are no longer used due to changes in the bracing configuration, were left open for a period of
time. After the discovery of marine borer attack, bolts were inserted into the open holes to
prevent access. However, the bolts have typically failed as a result of corrosive deterioration.
Other holes typically became open when the bolts attaching the timber bracing members failed
due to corrosive deterioration.
The galvanized steel bolts used to secure battered piles to plumb piles and timber bracing
members to the piles typically exhibit severe corrosive deterioration throughout the bridge.
Repair Scope: The creosote preservative in the existing timber piles have contributed to a
relatively long service life for piles in this environment. However, significant splits and checks
in the piles, significant loss of preservative chemicals in a large number of piles, continued loss
of chemical preservatives in the other piles, evidence of surface decay and significant potential
for internal decay, and evidence of significant marine borer attack all substantially limit the
remaining service life of the piles unless corrective action is taken.
Similar to the other timber elements of the bridge, there are options for in-place preservative
treatment of the piles including both internal and surface treatments. However, many of the same
risks and concerns for in-place preservative treatments of other elements apply to the piles with
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 38 Final Report