Houston - Shreveport line has a bridge over the San Jaciota river. More consequences from the earlier heavy rains ?
http://www.khou.com/news/local/train-bridge-sinking-in-kingwood-area/350860611
The San Jac is a pretty rough river…it ends up in Galveston Bay.
At least once a summer someone gets caught in a rip current in one of the bends along the river and drowns, and the bottom shifts all the time in some spots.
Last heavy bout of rain most likely scoured the pier bottom there.
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edblysard The San Jac is a pretty rough river…it ends up in Galveston Bay. At least once a summer someone gets caught in a rip current in one of the bends along the river and drowns, and the bottom shifts all the time in some spots. Last heavy bout of rain most likely scoured the pier bottom there.
They were fortunate that the alert employees were able to stop and remove the train from the bridge... Preventing a much more expensive and possibly very dangerous outcome for the crew on the train.
Several years back just north of Caldwell, Ks. [on the UPR's [nee; RI ,now UPR's OKT sub] a bridge pier was scoured out, under similar weather conditions. An alert engineer saw the problem and made an emergency application, but the momentum carried the two engines across the 'sag', and the crew was not injured.
Is there not a program of inspection on the locations of potential problematic bridges, by railroad employees, following a 'bad weather' event? It sort of seem like a bad plan to just send out a train to 'test' the line for a possible failure.
How old was the construction of that trestle bent/pier? I would be surprised if modern construction would have a pier bedding on material that would be subject to being scoured out by the river current. If not resting on bedrock, I would think the pilings would extend into stable sub soil where the river water would never reach.
I have seen a couple bridges over the Minnesota River fail by the river undermining piers. It also happed to the Mississippi River Stone Arch Bridge in Minneapolis during the flood of 1965; but those were all bridges built nearly a century earlier.
Sam: All railroads are out there in bad weather looking under the tenets of 49CFR213.239. The wildcard variable is what you can do under what conditions.
This one was a rapid failure on a bridge with steel H-piles driven to refusal or a really high blow count. Did UP witness failure due to limestone caving and degradation? (Karst strata topographic failure, more common in central and west TX, but...) Uncle Pete got a good surprise out of this and is probably looking at the bridge records for any past hint of trouble missed.
EuclidHow old was the construction of that trestle bent/pier? I would be surprised if modern construction would have a pier bedding on material that would be subject to being scoured out by the river current. If not resting on bedrock, I would think the pilings would extend into stable sub soil where the river water would never reach.
Its a steel pile trestle with a concrete deck so its probably less than 50 years old.
I doubt the piles were driven to bedrock since its on the Gulf Coast. More likely the piles are driven to a point where there is enough friction to support the load.
That of course requires there to be material around the pile to create the friction. If the river erroded 20-30 ft deep around the piles then there might be enough reduction in friction to cause them to shift. The San Jac River is normally muddy and would have zero visibility, Diving would be dangerous due to currents, the only way to "look" at anything would be to employ sonar.
Dave H. Painted side goes up. My website : wnbranch.com
All the rain in the past few months certainly has and will cause problems. We think that so few failures so far is hard to believe. UP, BNSF, & KCS certainly have their work cut out to vet all the bridges on each route.
https://www.google.com/maps/@30.026621,-95.2557038,285m/data=!3m1!1e3
Limestone all over, note the water is not all that deep here...the "island" is a favorite party spot for folks.
That is an old MoPac line, that bridge was built about the same time the old highway 59 bridge to the left was built.
http://www.historicaerials.com/aerials.php?op=home
link to find an older view.
Island doesnt show up till late 80s...as the water levels fall, more of it is exposed.
As we've seen recently, it's generally accepted - though not widely known - that more bridges are damaged or destroyed by scour and undermining, etc. than by overload or being struck by something underneath or a shifted load (except through trusses when the end portal is hit - that's the bridge equivalent of being cut off at the knees).
What this also illustrates is the resiliency of railroad bridges generally. Aside from their robustness due to the loads they carry, they're almost all 'simply supported'. That's too complicated to explain here, other than the main members are not 'continuous' across each pier, but instead have a joint there so they can move independently of each other. That may seem to be a weakness - and does make them a little more expensive - but it provides a way to accomodate large settlements such as these. Any continuous bridge would have been functionally destroyed by this amount of deflection; with a simply supported bridge, the repair is mainly just jacking up the spans and setting them on a new pier or bent.
Another possible geotechnical cause could be slippage of the foundation rock or soil (on which the bridge is supported) along a bedding joint, cleavage plane, or weak soil stratum, etc. I understand one of the tower bents for the new Kate Shelly Bridge had that problem. Here, the increased water might have gotten down that far to lubricate the joint enough to cause that to happen. Ask the folks in Oklahoma - who've been experiencing earthquakes associated with pumping wastewater into injection wells - about that.
- Paul North.
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