Retrofit of stub abutment 2

[tmalik3156]

Good day all.

Owner is afraid that flood will wash away the embankment, and the stub (perched) abutment will collapse. Abutment is on spread footing with no piles underneath. This has happened to some other bridges (a random example shown below).




So, we are doing a preliminary conceptual retrofit design.
We have heard about the following strategy:
1. Drill piles adjacent to the abutment (both sides)
2. Construct a cap on the piles
3. ''Connect'' the existing abutment with this new cap, as if the abutment has now ''extended'' and is being supported on piles at the ends.

Has anyone done similar design? How does the ''Connect'' work? Using large number of dowels? When the soil underneath the existing abutment fails, the existing abutment will behave like a beam, supported only at the newly extended ends. What can be done to efficiently transfer the moment and shear to the newly installed piles?

Alternately, we can squeeze in I-beams transversely under the girders and support that I-beam on the new piles.

Any suggestions?

 

[Lomarandil]

You could connect with epoxied dowels, or PT rods passing through the existing abutment and clamping your new cap to the abutment.

You could install low-headroom piles through holes cored in the existing abutment, then grout them in place.

If your girders can handle a relocated support, I like your last idea.

 

[BridgeSmith]

Drilling or driving piles in front of the abutment is problematic, at best, and extending the superstructure to new foundation supports behind the existing is equally, if not more, problematic.

Possibly , you could knock the back edge off the footing, drive piles right behind the backwall, drive another row of piles a few feet farther behind the abutment, and then extend the abutment back to encompass the front row of bearing piles, and the back row of 'hold-down' piles, to mitigate the eccentricity moment.

Armoring the embankment (riprap, revetment mattresses, etc.) to prevent it from washing out would seem to me to be the better and more economical option.