Why doesn't Lousianna use dirt grading for bridge approaches.

[roadman65]

I noticed that along I-10 around New Orleans that there are no dirt ramps that lead to overpasses.  It is all  bridge from the ground up to where it drops back down to land.  Is there a dirt shortage in this area, or something uncomprehensible to us?

[NE2]

Gators will eat the dirt. Don't you know anything about swamps?
Post Merge: May 07, 2011, 10:23:38 PM
Seriously, I would assume it's because of the lower environmental impact in the swampy terrain.

[Revive 755]

I'd go with dirt shortage; there are at least a couple spots in northern Illinois where the soil is of such low quality that a road is basically built on a bridge, but the bridge is covered with dirt anyway.  I have also heard of using foam blocks to support a road and then covering them with dirt in swampy areas; not sure why this one couldn't be used around New Orleans.

[J N Winkler]

It is not any of those reasons.  Swampy soil is very organic and therefore highly compressible, so it can't be made up with a bearing ratio high enough to allow it to be used in embankments.  Highways through swampland therefore tend to have very high structural content unless the swampy soil is excavated all the way to solid rock (which can be a very expensive proposition).

[Alps]

I think Reply #2 is basically the same as Reply #3, just worded in plain English. It's not so much a "dirt shortage" as a "shortage of the right kind of dirt." And yes, if swampland counts as wetland, a properly designed bridge cuts way down on impacts.

[J N Winkler]

And yes, if swampland counts as wetland, a properly designed bridge cuts way down on impacts.

I was under the impression that most of the New Orleans freeway system was built in the 1960's, before NEPA, the Clean Water Act, and the Section 404 permitting process all came along.

[UptownRoadGeek]

New Orleans basically sits on river silt. You would have to bring in dirt from at least 20 miles away to build embankments.

[SSOWorld]

That was my impression - I thought - why not dig in holes to route roads under?  You can't.  What UptownRoadGeek said and the fact that New Orleans is below sea level in several places.  The long bridges for I-10, I-310 and I-55 are because of swamp.  the Atchafalaya Swamp between Baton Rouge and Lafayette is pretty wide in itself (the bridge is 18 miles long) The Manchac Swamp Bridge (I-55) is 23 miles wide - then you have the additional 8 for I-10 over the Pontchartrain spillway

I was quite perplexed by all of this when I drove through on 2/15, but not surprised.

[vdeane]

Even using regular dirt, it would probably just sink down.  You can't even bury people below ground over there without running the risk of the body washing up somewhere.

[Darkchylde]

Even using regular dirt, it would probably just sink down.  You can't even bury people below ground over there without running the risk of the body washing up somewhere.

Hence all the above-ground cemeteries over there. Can't miss 'em, there's a bunch around the Metairie road exit on I-10.

[codyg1985]

Even using regular dirt, it would probably just sink down.  You can't even bury people below ground over there without running the risk of the body washing up somewhere.

Yep, the organic soil below would still consolidate over time which would create some very undesirable differential settlement in the embankment. The very high water table doesn't help matters, either.

Bedrock is very far below down there, too. It is hundreds of feet down. Friction piles are what hold everything up down there.

[longhorn]

Even using regular dirt, it would probably just sink down.  You can't even bury people below ground over there without running the risk of the body washing up somewhere.

Yep, the organic soil below would still consolidate over time which would create some very undesirable differential settlement in the embankment. The very high water table doesn't help matters, either.

Bedrock is very far below down there, too. It is hundreds of feet down. Friction piles are what hold everything up down there.

Before they rebuilt and paved over the original concrete on I-10 between Baton Rouge and New Orleans, there used to be some serious dips, actually was kinda fun for the kids, but not so much doing 70 mph.

[longhorn]

That was my impression - I thought - why not dig in holes to route roads under?  You can't.  What UptownRoadGeek said and the fact that New Orleans is below sea level in several places.  The long bridges for I-10, I-310 and I-55 are because of swamp.  the Atchafalaya Swamp between Baton Rouge and Lafayette is pretty wide in itself (the bridge is 18 miles long) The Manchac Swamp Bridge (I-55) is 23 miles wide - then you have the additional 8 for I-10 over the Pontchartrain spillway

I was quite perplexed by all of this when I drove through on 2/15, but not surprised.

I remember when they built the Atchafalya bridge in the 70s. Traffic used to detour over 190 between Baton Rouge and Lafayette during construction. Still do at times when their is a crash on the bridge. Its hard to imagine its only 19 miles long, seems much longer. And patroled very heavily, I wander how much money La. gets from the speeding tickets on that 19 mile bridge.

[lamsalfl]

Please note that I-49 is slated to be elevated from the current end of the elevated Westbank Expressway to Raceland whenever they decide to secure funds to build it.  LA will hold claim to the majority of the top 10 longest bridges in the world.

[longhorn]

Please note that I-49 is slated to be elevated from the current end of the elevated Westbank Expressway to Raceland whenever they decide to secure funds to build it.  LA will hold claim to the majority of the top 10 longest bridges in the world.

To Raceland? Don't you mean to Avalon? What would be the purpose to build a bridge to Raceland?

[pctech]

The native soil doesn't have the proper load bearing qualities. The ground in the New Orleans area is settling as well. It has made for some entertaining "jump ramps" where a bridge meets the surface road. Why they chose to use concrete to  build highways under such conditions has always perplexed me?.....knowing it's going to sink and buckle.

Mark

[lamsalfl]

Yes Raceland.  The road will be over wetlands for much of the way.   Where is Avalon?

[Anthony_JK]

Yes Raceland.  The road will be over wetlands for much of the way.   Where is Avalon?

I believe that that was supposed to be a joke.

The reason they want to fully elevate I-49 South from Raceland (actually, the interchange with LA 1/LA 308/Bayou Lafourche) to the Westbank Expressway) was to not only cross over the span of wetlands, but also to support hurricane evacuation through a roadway placed above the 100-yr. coastal floodplain.

[apjung]

The native soil doesn't have the proper load bearing qualities. The ground in the New Orleans area is settling as well. It has made for some entertaining "jump ramps" where a bridge meets the surface road. Why they chose to use concrete to  build highways under such conditions has always perplexed me?.....knowing it's going to sink and buckle.

Mark

I can name some jump ramps still in and around the area that need to be be patched up including:
* The start of the Harry Lee Expressway (at the end of the older Crescent City Connection) where the right 2 lanes have the jumping sensation so I merge into the far left lane to avoid it.
* Power Blvd Entrance jump ramp to I-10 East in Metairie
* US 90 has numerous jump ramps between Raceland and Houma.

Former jump ramps included:
* I-10 at the Jefferson/St. Charles Parish line
* Airport Access Road bridge
* I-310 at the southern end of the 5 mile viaduct
* US 61 jump ramp to I-310
* I-55 jump ramp at the northern end of the Manchac Swamp Bridge
* numerous bridges and overpasses on I-610

[pctech]

The interstate system through New Orleans should have been built elevated or the surface sections built on friction pilings. I know that would been costly, but it wouldn't have settled. The roads in the city itself are in terrible condition for the most part.

Mark

[codyg1985]

If you look at this aerial imagery showing the widening of I-10 between Clearview and Veterans, you can see how the approaches to the bridges are being constructed.

[longhorn]

If you look at this aerial imagery showing the widening of I-10 between Clearview and Veterans, you can see how the approaches to the bridges are being constructed.

I know we are talking about approaches, but if one pans out and sees the Causeway / I-10 interchange, that is one weird modification of a clover leaf. For years the bridge supports were built but nothing done with them.