770.9 miscellaneous bridge maintenance
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Some of the miscellaneous bridge maintenance items normally performed by district routine maintenance forces include:
1. Drift - Drift or debris that impedes the stream flow shall be completely removed as soon as practical for scour critical structures and with higher urgency than routine maintenance for non-scour critical structures. Collections of drift around or under bridges may alter the course of the stream, may cause scouring and undermining and may constitute a fire hazard. Drift shall not be permitted to become silted in as this alters the channel and provides a footing which will catch drift that would normally float past the bridge.
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During periods of high water, the drift may be dislodged from the bridge and allowed to float downstream. Drift remaining after the high water has receded should be removed from the vicinity of the piers, bents, etc., and burned or removed. It should not be piled in the center of the waterway for the next high water to wash away. If it cannot be removed promptly, it should be cut up in approximately 5 ft. lengths in the hope that succeeding high waters will remove it or at least not permit it to catch more drift.
Cranes with clam buckets or grappling hooks and motorgraders with cables and hooks are usually used to remove drift. It is often necessary to use a chain saw to cut up the drift before it can be removed. As always, the safety of the personnel is of prime importance, but care must also be exercised to prevent damage to the handrail, curbs, piers, etc.
2. Scour - Areas adjacent to piers or abutments which are scouring, or where there is a possibility of scouring, should be protected with type two rock blanket in accordance with Sec 611.30 of the Missouri Standard Specifications for Highway Construction, a rock fill or grouted rock. Rock to be grouted should not be choked with fines. Use thin grout and allow grout to penetrate the fill to make a solid unit. When placing bank protection, a toe wall shall be constructed along the bottom and both sides to prevent undermining.
Areas subject to scour should be monitored closely during flooding or other periods of high water
3. Erosion - All erosion of fill slopes at a bridge should be backfilled with suitable material and compacted. Paving with a bituminous mat is an effective method to prevent recurrence. In cases where the fill has eroded exposing the bottom of the abutment cap, the erosion should be repaired by backfilling around the abutment and mudjacking any remaining voids.
4. Rodents - If the fill in front of the abutments is not maintained approximately 12 in. up on the caps and wings, rodents will burrow underneath and undermine the approach fills and cause settlement of the roadway. The best method of eliminating these rodents consists of filling the burrows with hot asphalt and filling the holes with earth and rock.
5. Vegetation - Weeds, brush, or other vegetation must be eradicated or controlled by mowing, spraying, or cutting, and stump spraying. Weeds and brush provide good cover for rodents and permit them to go undetected.
Vegetation around timber piling or timber backwalls can best be eliminated by scalping the area, sloping it to provide drainage, applying soil sterilants and priming and sealing with asphalt. These areas should be checked often during the summer months for effectiveness to prevent fire hazards and care should be exercised not to permit cut brush and weeds to be piled near the bridge.
6. Dirt and Debris - It is important that bridge decks, sidewalks, curb outlets, drains, chords, and bent and pier caps be cleaned as often as necessary and thoroughly cleaned in the early spring to remove deposits of winter abrasives and chemicals. Decks should be cleaned whenever dirt or debris accumulates during the year and before the application of seal coats or bituminous mats. Snow and ice control abrasives and chemicals should be flushed from the decks regularly. Dirt and debris on the decks, caps, etc., will retain moisture allowing it to penetrate the concrete. Dirt or other foreign material, in the drains or curb outlets allows water to remain on the deck where it could freeze causing a hazardous condition for motorists. Care should be exercised when cleaning the decks and outlets not to shovel dirt onto the lower chords, girder ends, or paved slope protection.
Cleaning necessitated because of the application of snow and ice control abrasives and chemicals is to be charged to Activity Code R913.
Routine cleaning, including the required cleaning prior to the application of seal coats or bituminous decks, is to be charged to the bridge and Activity Code R322.
The right-of-way under and around the bridge should be kept free of debris. This will permit the area to be mowed easier and not attract more debris. If necessary, NO MORE TRASH (R5-26) or NO DUMPING (R5-28) signs should be erected.