New Piles to be installed under an existing in service Abutment

[jhgestimator]

We are exploring how we can install new piles under an existing bridge abutment, this is in order to provide support directly to the rock below the fill rather than rely on the abutment sitting on a reinforced earth fill embankment. The bridge is a freeway structure with super T beams and is under traffic.We would be interested in any previous experiences or idears in completing this task.Options we have to date include; underpinning by hand work from the bottom up, UBP from the top down, through the existing and then trying to connect the existing to the new pile, or maybe jet grouting.Thanking you in anticipation of some good idears

 

[Ron]

Not sure what your local codes allow, since you don't state your locale; however, grouting to provide continuity between your bearing surface and a competent bearing layer is probably the easier of the options to accomplish. Pinpiles or similar might be a possibility, depending on how accessible the foundation bearing might be (such as having to core through the existing cap or bent to provide access).

 

[oldestguy]

Explain why this consideration. Is the MSE wall moving outward or settling? Do not you have sufficient bearing for the deck system to move with respect to the moving abutment?

If it is only settlement, does the vertical alignment of the roadway become a problem with these movements? Many a bridge exists like this.

Holding up the abutment while the MSE fill settles leads to another problem of how to go from settled fill to a bridge that is higher. Approach slabs of considerable length may also be needed. (A ski jump?)

If it is concern for the fill and the MSE materials moving laterally, vertical piles or almost any support in that fill will bend laterally also.

Sounds like batter piles are in order if the wall lateral movement is possible.

Not a simple thing this. Maybe live with it.

 

[Qshake]

If you're after a method that will allow traffic to remain on the structure, I think it's going to be tough.

For all the trouble you'd have to go through it may be best to have lane drops in off hours and use micropiles to bear in the rock below the MSE wall fill. Micropiles are drilled in so they eliminate pesky vibrations and large equipment next to traffic.

One problem to consider with the existing abutment is coring through the reinforcing steel, unless you're abutment is just one massive compression block. If the rebar in the abutment is more than temperature and shringkage you'll likely cut into it and you don't want that.

If you core into the existing abutment and use pile you'll be redefining the abutment from a compression block to a beam supported on pile. So the question becomes how to reinforce the existing chunk of concrete between and across the piles. That can be very laborous.

Seems like tearing it out and starting anew is best.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Qshake]

I didn't get a chance to read oldestguy's post before writing.

In my experience it's rare to see a bridge abutment founded on an MSE wall fill. Not that it can't be done; the MSE wall manual by the FHWA allows for this. Most DOT's don't use it for the same reason they don't use spread footings on soil....settlement.

The settlement may not be the actual granular backfill for the MSE wall but rather the soil on which the MSE wall backfill bears on. In the midwest, most abutments are founded on pile which is driven first and granular fill placed around the piles. Often the piles are in a CMP or Sonotube sleeve with loose sand placed in the annular void. This, of course, mitigates downdrag on the pile due to settlement of either the insitu soild or granual backfill.

I have seen DOT manuals that allow spread abutments on MSE wall fill. Ohio DOT comes to mind. But it's extremely important to check the limit state of settlement.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[sunny7uc]

Compaction Grouting is probably a solution you are looking for. Pin Piles/Micropiles will be probably more expensive as it will require structural slab/grade beams. Compaction Grouting can be done in phases to keep the traffic open.

 

[jhgestimator]

Thank you guys,
The problem bridge(s) are in Melbourne, Victoria on the Western Highway. The underlying soils are expansive clays. The road authority, VicRoads, has had issues of on some earlier bridges where the settlement has caused drmatic issues. The bridges in question were constructed in the early '90s and the highway is to be widened, and therefore VicRoads want to take the opportunity to retofit piles under the existing abutments to prevent future settlements.
The constructon process described that is used in the midwest is now common place here.
We are concerned about drilling through the RC abutment and losing the intergretity of the reo. Hydroblasting through is one thought as is the micropiles and jetgrouting.

 

[Qshake]

Thanks for the additional input and for broadening my horizons beyond the USA. I often forget this website is frequently used by the international engineers too.

Good luck!

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[hokie66]

What goes under the bridges? Solutions might vary depending on whether it is a road overpass, railway overpass, or is over a stream or drainage channel.

What are the elevations involved? Depth to rock, thickness of clay under RE embankment, height of RE.

Have you done a geotechnical investigation? Is settlement of the bridges in question currently a problem? If so, has the problem been isolated to the clay layer or to the embankment material?

 

[qhtony]

jhgestimator, I think the problem you described lies in two scenarios:

1. Settlement of the bridge abutment caused by consolidation of the expansive clay
2. Deformation of the reinforced fill (which in turn affects the bridge abutment) caused by the shrinkage/swelling of the expansive clay.

As to consolidation settlement, if the bridge was built in the 90's, don't think it has much of further impacts to the bridge abutment (2011) since the consolidation should have finished after 20 years (unless the clay layer is ridiculously thick).

Would the deformation be more of your concern in this case? As the clay is likely to subject to periodic seasonal moisture change which makes the shrinkage/swelling possible. My past experience with reinforced fill is it can be quite deform-able if the founding material deforms. This is probably why bridge abutments move as well because they sit on the fill.

Agree with OldestGuy, if you were going to put piles from top down, you may want to consider any lateral actions posed by the movement of the reinforced fill.

 

[jhgestimator]

Thank you everyone for your input. Unfortunately we did not win the tender. Our solution, albeit extreme ended up being a major excavation (2m x 2m) slot under the abutment to enable excavation down to rock/suitable material then creating a pile from there up to the underside of the abutment. Repeating the process for the appropriate number of “piles”.
The bridges all are freeway over local road/arterial road.

Regards
Ken