Reinforced Earth Bridge Abutment

[Steeleguy]

I am working on several Bridge Replacement projects and looking for imput on utilizing reinforced earth abutments. These bridges are very low volume 10 ADT ~ farm to market crossings. Normal practice is to drive piling to glacial till deposits 75' - 200' below grade. In doing this the bridge is ridid and the approaches are not. severe settlement occurs seasonally and is a continual maintenacne / safety problem. The clay soil deposits are low density high moisture and very expansive. Has any one built reinforced earth abutments to carry short span steel bridge and traffic on low density high moisture expansive clay soils. Soil bearing capacity can be as low as 1500 psf. Piling to these depths (75' -200') for low volume crossing seems to be overkill. Any comments appreciated!

 

[hokie66]

Yes, it is done. Suggest you talk to Reinforced Earth about it. One thing to consider...you have to have a source of appropriate material to form the reinforced earth embankment. And the bearing on the reinforced earth has to be substantially back from the face, so the bridge span is actually longer. Using this method, you would not eliminate the problem of the approach settlement, but would probably reduce it.

Do you use relieving slabs at the approaches? That would help a lot with the required maintenance.

If you stick with piling, you should investigate founding higher than the 75' - 200' rock. I agree that is overkill. I would look at expanded base cast in place piling (Frankipiles), founded at maybe 20'. Talk to Franki or a specialist piling contractor in your area.

 

[Steeleguy]

The owner has a great aggregate pit for embankent, had planned on using Geo Cell sub structure and separation fabrics may be even a little tri-grid in areas. Want to utilize corrugated steel panels to the abutment for the shell surface. Would encorparte into the GRS abutment. Would like to have non-pile driving contracter to install. Thanks for the input!

 

[Qshake]

Very few states permit setting an abutment directly on MSE fill. Single largest concern is settlement of either the wall fill or more likley the insitu soil under the granular backfill. If the insitu soil can't support the weight of the wall typically stone columns are used to strengthen the existing soil and that's an expesive venture.

Most counties and cities try to follow state guidelines due to funding mechanisms so even though it's not a state agency they may still take a dim view to seating on MSE wall.

if you do have an abutment on MSE wall, you'll want to have an open seat abutment so if the abutment settles it won't induce stress into the superstructure as it would for integral construction.

Sometimes it doesn't pay to go the cheap route just a lot of headaches later.



Regards,
Qshake

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