Ned Pelger's blog on construction, design and other weirdness. Email him at ned@constructionknowledge.net
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CONSTRUCTION KNOWLEDGE BLOG
August 19, 2010
World Record Caisson Capacity in St Louis Bridge
In reviewing a structural engineer’s plans yesterday for a Fitness Center, I noticed the requirement for the contractor to verify that the existing footing can support 2.75 tons of load per foot. We are raising the roof on an old auto dealership and providing for a future second floor. I considered the structural engineer’s note and thought we should be able to check the existing footings and verify the capacity.
This morning, though, I read an article in ENR about the other end of the continuum. A bridge being built to cross the Mississippi River near St. Louis just tested a single drilled pier to a capacity of 36,067 tons. That’s a world’s record for a single drilled pier load. Looked at differently, it’s 13,115 times more footing capacity than I need.
The 11.5′ diameter drilled caisson was 43′ under water with a 23′ rock socket into the limestone. The test caisson had 18,000 ton end bearing and 18,000 side bearing in the rock socket. Normally bridge caissons are 5′ to 8′ diameter and would require many more caissons for each foundation pier. By proposing and testing this larger caisson, the contractor will be able to greatly reduce the number of caissons and save 3 months of construction time.
I love America and our gusto for pushing the limits and grabbing the rewards that come from figuring out a better way. For all the nattering nabobs of negativity out there, I predict America will rise from this Great Recession strong and competent. The rumors of our death are greatly exaggerated.