Enter Sand, Man
From Page 43 of the U.S. Army Corps of Engineers' Trinity floodway report
Astute Friend of Unfair Park "Wylie H." drilled into the U.S. Army Corps of Engineers' report on the Trinity River levees yesterday evening and found the real horror story that goes almost unmentioned in this morning's Dallas Morning News account of the report: the story of the day we almost lost the Margaret Hunt Hill Calatrava signature make-believe suspension bridge.
Do you know that most city council members haven't even read this thing? Hail to the bloggers!
I will reproduce the language from the report below. But first, let's focus on what this means.
The scenario I painted in a March 26 column -- "sand boils" erupting like little volcanoes and tearing out the levees -- may have been understated. Something happened out there with the drilling of piers for the Calatrava make-believe suspension bridge so dangerous that it forced the U.S. Army Corps of Engineers to go back and re-examine the entire levee system.
The result of that reexamination is the report released yesterday -- a devastating indictment of everything the Corps itself and local officials have done on the Trinity in the last 30 years. Something really bad happened out there. The problem is, you and I still don't know exactly what it was or what it means. And the mayor has already made it clear: Instead of calling for public hearings on what went wrong, he is going to press ahead with plans for building a multi-lane toll road right on top of the area where this incident occurred.
What did occur? Here is the language the wiley Wylie H. excavated from deep within the Corps report:
"During the drilling of piers for Bent 6 (located 300' from the wet side toe of the west levee), the contractor reported that large quantities of sand in the formation liquefied even though slurry was being used to hold the excavation open. The liquefaction was so extensive that it destabilized the area within a 20' radius of the 7-foot diameter pier. This area had to be backfilled in order to be able to support the drill. When drilling resumed, a casing was used to support the excavation. However, the bottom of the pier heaved and blew out. The pier excavation was finally completed using both casing and slurry. During concrete placement, the contractor was unable to remove the casing with a 200-ton crane, so it remains a permanent fixture within the Floodway."
In plainer English? They're trying to drill a 7-foot diameter hole out in the floodway approximately 90 feet down to bedrock. They're injecting a watery slush into the hole to blow the dirt out. The slush hits sand somewhere, and when it does the slush turns the sand into a liquid.
This is exactly the condition I was talking about in my March 26 column. Water under pressure "boils" the sand. The effect is to turn an area around the drilling rig with a 20-foot radius -- that would be a 40-foot diameter -- into something like quicksand. It's enough to threaten the drilling rig.
They take the rig out, I assume. They pile in dirt to try to stabilize it. Then as they begin drilling again, they sink a "casing" -- sounds like what I would think of as a caisson -- into the drill hole. I assume it's a big round pipe shoved in there to keep the liquid sand from continually caving in and filling the drill hole.
Once they drill the hole that way, they are supposed to have a tubular void to fill, and they are supposed to know the exact volume of that hole, so they know exactly how much concrete to put in. Computer tells them. But they keep pouring and pouring. Pouring and pouring. The hole eventually slurps up twice the volume of concrete it's supposed to hold. That means they don't know where the concrete is going.
When it's time to pull the casing out, the biggest equipment they can get down there to do the pulling can't budge the pipe. It's supposed to be removable like a concrete form. But the casing won't come out. They have to leave it there. That means the concrete they poured into the hole squished out around the casing somehow, hardened and locked the casing into the ground.
So, all this jumble of crap is still down there.
They know that when the river floods, water under tremendous force will push down along that casing and find that same sand again. Try not to drive on the make-believe suspension bridge that day!
Look, this "expert" analysis was prepared and written for you by James W. Schutze, B.A. English and Political Science, University of Michigan, 1971, also a former member of the Michigan State Employees Credit Union. If you feel fairly reassured by this analysis, I think you may need to go see a doctor, because you could be nuts.
All I know for sure from the Corps report is what Wylie knows: Something really really bad happened. Something chaotic. And you know what really scares me? Leppert's eyes. The mayor of Dallas has still got that absolutely crazed and glazed look on his face, telling us that, by George, we're gonna just forge ahead and, by golly, we are gonna just build a lot of stuff out there no matter what.
You know what we need? We need city council member and toll road foe Angela Hunt to convene her own citizen inquiry. Those other zombies on the city council won't do it. And somehow we need her to jaw-bone the Corps and the contractor and objective experts to come sit down in front of cameras and microphones and answer the real question that I see bubbling up out of the sand on Unfair Park from our astute commenters: WTF?
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