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Interstate 10 closed indefinitely between AZ & CA


Re: Passed inspection ...

This section of bridge " passed inspection " in March of 2015 .... :confused:
I'm quite sure what happened here is the higher than designed volume of water undermined the footings and caused the collapse. This happens frequently on bridges that are too small to pass this much water. When a bridge restricts the flow the water velocity will increase and erosion will take place. When the volume drops back down slower water will frequently drop silt and other material into the scoured area, filling it again. The only time you can detect this is while it is at flood stage. It can be predicted based on soil types but can't be measured unless the inspection is done while at flood stage. I used to inspect bridges. You wanted to go look when it was flooding but frequently you couldn't even probe the footings because of the high water velocity and trash coming downstream.

---------- Post added at 03:54 PM ---------- Previous post was at 03:50 PM ----------

I shudder when I see TV pictures of people standing on a bridge and watching the flood. Unless the water is moving slow you don't have any idea what is going on at the bottom. The bridge may not be in danger of being washed away but depending on how the foundation was built it can be in danger of collapse.


A friend of mine is a bridge inspector. Before that he was a crane operator for the bridge department. Part of his job then was to remove debris from against the bridge supports in the water with a clam bucket.
It is amazing how much more force the water has on a bridge when it is pushing on trees and stumps and garbage.
The flow in the wash was thrown out of the channel center by sediment or by the volume of the flow, and washed out the abutment. Yes, you can design for this, but you (the public) doesn't want to pay for design and construction for every possibility. California designs for earthquakes (duh) and the bridge inspectors look for scour, but desert flows are unpredictable, and it is kind of hard to design for everything on a budget. You pick your design targets based on what is reasonable to expect.

I worked on an emergency job for Caltrans, a bridge on I-5 (think Major Busy Freeway) showed scour under the pile cap. They attached tiltmeters to the bridge, hardwired to a phone line, so they could close the bridge soonest if it started to move. I thought it would be fun to wack the tiltmeters with a rock hammer to see what would happen, but was talked out of it

David Hughes
Engineering Geologist, Caltrans


Anyone know the latest on this area of I 10 interstate? Planing to go to that area of the country in a month or two, May or June 2016. Thanks :wave::wave: