Old Spanish Trail Bridges over Atchafalaya River in Morgan City, LA

(Satellite)
1933 Truss: (Bridge Hunter)  50' or 60' clearance depending on source
1977 Cantilever: (Bridge Hunter)  73' clearance [marinas]

During the "good roads" period at the beginning of the 20th Century, the Old Spanish Trail was built along the Gulf Coast. It was substantially completed to California by the 1920s except for two significant gaps: the Mississippi River in New Orleans and the Atchafalaya River in Morgan City. (The New Orleans gap was closed two years later by the Huey P Long Bridge (NO).) The piers for the long, heavy trusses would be sunk in many millennia of deposits from the Mississippi River, so I wondered how deep the piers were. So I dug deeper. (Pun intended) It turns out that a pier set a world record depth of 175' and the 608' long spans were also a world record in 1933. [StMaryNow-Bradshaw]

The Old Spanish Trail became US-90. When the four lane E.J. Lionel Grizzaffi Bridge was opened in 1977 as part of a road improvement project for US-90, the Long-Allen Bridge was redesignated LA-182.

C Hanchey Flickr,  License: Attribution-NonCommercial (CC BY-NC)
Old U.S. Hwy 90 bridge on the left and new U.S. Hwy 90 bridge on the right.

1933 Long-Allen Bridge

C Hanchey Flickr,  License: Attribution-NonCommercial (CC BY-NC)

Long-Allen Bridge (Morgan City, Louisiana)

Historic Long-Allen Bridge on old US Hwy 90 over the Atchafalaya River between Berwick and Morgan City, Louisiana. The bridge is a Parker through truss (K-Truss). It was built in 1933 by the Mount Vernon Bridge Company.

I was wondering how many 100s of feet it was to bedrock. I've learned that I should be thinking about how many 1000s of feet it is to bedrock! And the bedrock is gooey. "I know the drilling usually firms up around 5,000 feet or so." [redstick13 comment in TigerDroppings] In fact, you have to go down a ways just to find competent sand. The following is for New Orleans: "This allowed large quantities of graveliferous deposits beneath what is now New Orleans, reaching thicknesses of up to 3600 feet (Figures 3.2 and 3.3). These stiff undifferentiated Pleistocene sands and gravels generally lie between 40 and 150 feet beneath New Orleans." [Page 3-2 Katrina Levee Report] Bedrock is probably even deeper in Morgan City.

Now days, when bedrock is too deep, piers are built on friction pilings. Back then, they evidently used a "friction pier." As mentioned, the 175' pier set a new world record. I learned that ABC, Accelerated Bridge Construction, is not a new technique. The 1,400-ton spans were floated into position and lifted 60' onto the piers.[StMaryNow-Bradshaw]

Boston Public Library Flickr via Bridge Hunter, License: Creative Commons Attribution (CC BY)

I don't normally bother with portal views, but this old bridge has some seriously deep K-trusses.

Street View

Street View

1977 E.J. Lionel Grizzaffi Bridge

C Hanchey Flickr,  License: Attribution-NonCommercial (CC BY-NC)
1975 cantilever truss bridge over the Atchafalaya River between Berwick and Morgan City, Louisiana

Note the seawall. When I tried to get a street view of the RR bridge from Front Street, my view was blocked by that seawall. This river doesn't get wider, it just gets higher.

Street View

Street View

Unlike Illinois and Kentucky, Louisiana understands that it is cheaper in the long run to maintain truss bridges. Louisiana planned to spend $12m repainting and repairing the US-90 bridge. The repairs consist of structural repairs such as replacing some of the bolts and rivets. They also plan to spend $16m to rehabilitate the LA-182 bridge. [StMaryNow-rehabilitation] Unfortunately, only repainting and structural repairs are mentioned. I noticed that Bridge Hunter records a rating for the substructure as "serious" (3 out of 9). They have installed counter measures to mitigate a problem with scour. [BridgeReports] Is "scour" the reason for the "serious" rating, or are some piers sinking?