Bridge ends

[hbelkins]

Do all states have trouble with their bridge ends settling on new construction projects, or is Kentucky especially vulnerable to this?

They've already had to wedge up the bridge ends on the new four-lane Mountain Parkway section in Wolfe, Morgan, and Magoffin counties because the fill at the ends of the bridges has settled.

[wanderer2575]

Not sure if you're talking about the bridges themselves, or the pavement approaching the bridge.

To the latter:  Not too long (a half-dozen or so years) after construction of the I-94 Gateway Bridge over US-24 in Taylor MI, the approaches settled so much that MDOT had to replace a few hundred feet of base and pavement in every lane on both sides of the bridge.  There are still noticeable bumps when driving on and off the bridge.

[Dirt Roads]

Do all states have trouble with their bridge ends settling on new construction projects, or is Kentucky especially vulnerable to this?

They've already had to wedge up the bridge ends on the new four-lane Mountain Parkway section in Wolfe, Morgan, and Magoffin counties because the fill at the ends of the bridges has settled.

Not sure if you're talking about the bridges themselves, or the pavement approaching the bridge.

To the latter:  Not too long (a half-dozen or so years) after construction of the I-94 Gateway Bridge over US-24 in Taylor MI, the approaches settled so much that MDOT had to replace a few hundred feet of base and pavement in every lane on both sides of the bridge.  There are still noticeable bumps when driving on and off the bridge.

This is a potential three-piece issue.  I think that hbelkins is referring to the concrete abutments at each end of a bridge structure.  In some states, that component seems to settle first.  West Virginia tends to have the problem that wanderer2575 mentioned, where the approach to the concrete abutment settles and the abutment stay put.  But now with certain bridges in the Interstate system over 70 years old, I'm seeing more bridges where the bridge span itself is sagging a little bit right up next to the joint for the abutment.

These are all huge problems in my world, since rubber-tired trains incorporate power collection systems that require the power rails to have a tight vertical alignment.  We have to get this right every time.

For the case where the abutments are settling, this is a fairly common problem.  The abutments and the support piers should be designed using the same principles, whereby the support structure and pilings ought to go all the way down to the bedrock.  If you can't get down to the bedrock, the abutment (or the pier) is probably going to settle a bit.  On the projects that I've been around, the areas where the bedrock is deep is usually "overfilled" with a huge mound and allowed to settle for several years before that bridge element is constructed.  (Definitely not fun for the construction schedulers).  I think it is preferred to use spread footings, which are not always effective at preventing vertical subsidence.  There's also some techniques to stabilize the fill materials using flowable fill (loose concrete) and geosynthetic fabrics.  All of these techniques add to the cost and schedule of a bridge.  Since this type of construction occurs early in the project, it sometimes doesn't get the proper monitoring by inspectors.

Keep in mind that this is a three-dimensional issue, as some of the subsidence might be lateral or longitudinal with respect to the bridge, rather than vertical.  That's why most bridge abutments are protected with a 1:1 slope covered with heavy rip-rap.  Additionally, much of the force on a bridge is transmitted to the pier or abutment along the plane that the vehicles are moving, which is worsened on freeways and other bridges where all the traffic is only moving in one direction.  We also see issues with the harmonic frequency inferred by the traffic (trucks generate very low frequencies), which may excite the vertical concrete structures of certain lengths (particularly columns and pilings) so that they want to jump up-and-down.  I've got a friend who is world-renowned in the area of bridge element stiffening, and his stories are fascinating.

[hbelkins]

I probably should have done a better job explaining. We typically call them "bridge ends" but what's being discussed is the fill on the approaches to the structures themselves.

[Bruce]

Oregon had to scrap and demolish a half-built railroad overpass on US 97 near La Pine because of soil settling: https://www.bendbulletin.com/localstate/odot-highway-97-overpass-in-la-pine-scrapped/article_852de40a-8b2d-5169-bf96-de62075f2d15.html

[Bitmapped]

It's not an uncommon issue for bridge approaches to settle. That's why some states (including Ohio in many cases) like to use concrete approach slabs that span over settling. Other agencies (like PTC) often leave asphalt sections of otherwise concrete roads right around bridge approaches so it's easier to correct if/when settling happens.

[jmacswimmer]

Locally by me, 2 back-to-back bridges on I-695 over MD 26/Liberty Road & Milford Mill Road (replaced in 2012 & 2016, respectively) had the approaches resurfaced in the last year or 2. The bumps up from the asphalt approach to the concrete bridge deck had been getting pretty nasty prior to said wedging/resurfacing.

[roadman65]

US 90 in many parts of La, need to have serious grading done at bridges.  Obviously LaDOT didn't grade the freeway parts near Raceland, Houma, and Morgan City too well.

[froggie]

US 90 in many parts of La, need to have serious grading done at bridges.  Obviously LaDOT didn't grade the freeway parts near Raceland, Houma, and Morgan City too well.

Grading's not the problem.  Settling is the problem.  You can have the best grading job possible and it still won't make a difference if the embankment settles.

[hbelkins]

US 90 in many parts of La, need to have serious grading done at bridges.  Obviously LaDOT didn't grade the freeway parts near Raceland, Houma, and Morgan City too well.

Grading's not the problem.  Settling is the problem.  You can have the best grading job possible and it still won't make a difference if the embankment settles.

Seems to me it's a compaction issue.

Not only does Kentucky seem to have an issue with bridge ends settling, lots of fill areas are settling as well. The five-mile stretch of KY 30 in Owsley County between KY 11 and KY 847 is very bad, as is the new alignment of the Mountain Parkway between exits 72 and 75.

[JoePCool14]

I remember someone on this forum saying that WisDOT had issues with their bridge ends. Most of the bridges of I-41/I-94 in the SE region had their bridge ends redone with asphalt within the last year or two. And I have to say, some of them already appear to be settling. I wouldn't be surprised if those don't last more than 2-3 years at this rate.

I haven't noticed this to be an issue in Illinois, with IDOT or ISTHA.

[Urban Prairie Schooner]

US 90 in many parts of La, need to have serious grading done at bridges.  Obviously LaDOT didn't grade the freeway parts near Raceland, Houma, and Morgan City too well.

Occupational hazard of constructing a freeway through a swamp.