Bridge over Environmentally Sensitive Area

[f8r]

I am looking for a type of bridge construction that minimizes impacts to a marshy area that will be crossed. It will be a low-level (causeway type) structure, presumably on pile bents, with repetitive spans for approximately 1500' total length. A "Top-Down" type of construction would be desireable. Does anyone know of any projects where these considerations were a part of the design and construction?

 

[fuchsjr]

Depends on how much funding you have available, and your construction schedule. You could do a "launched" type structure using precast elements, with a cased drilled shaft substructure; depends on soil conditions.

 

[SlideRuleEra]

One design used for this situation is cast-in-place flat slab (often 30 ft spans) supported by driven steel H-pile. Pile driving, falsework erection/wrecking, and concrete placement can be performed by one fairly small crane from the bridge deck. The H-pile cause minimal disturbance and the simple, repetitive formwork is reuseable.
Depending on conditions, it may be possible to accelerate the schedule by working the project from both ends and meeting in the middle.

 

[f8r]

Funding is limited, scheduling is open - County Project in FL. I assume that construction will involve precast elements. Anticipated sequencing: drive piles for bent ahead, install pile cap, install precast slabs (or precast beams w/CIP Deck), advance crane, repeat process. This type of construction, I'm sure, has been done before. What I'm looking for is a project(s) that have been built this way, to get some idea of costs, and to ID successful construction techniques and other considerations.

 

[DRC1]

I have seen articles in the past on this. I think Civil Engineering had one a couple of years ago. In general, the piles were driven in front of the trestle, a pair of cap beams were installed and the deck placed. Spacing would be dependent on the crane - the larger the spacing, the heavier the crane, the stronger the deck. I would look at using timber piles to reduce cost, esp if lengths can be 60 ft or less. Timber piles will limit you to about 30-45 ton dependig on soil and pile size, but depending on bent spacing,that may not be a problem.