The problem wasn't that the contractors left the holes open so long that they allowed rainwater to fill them. The problem was that the drilled shaft company shouldn't have been in there drilling the holes until the steel cages were already tied, the centering wheels installed, and the concrete ready to go. At MDOT, they have a specification that no uncased hole can stay there more than 24 hours, and you HAVE to start pouring concrete into the hole no more than 2 hours after reaching tip elevation (for you Liberal Farts majors, that's the Bottom of the Hole).
The soil underlying DWS is Demopolis chalk, weathered overlying unweathered. I would estimate the weathered material was about 15-20 feet deep (from my memory of the holes for the bridges drilled for Hwy 25 and 82 in the late '90's). That the holes were 40 feet deep showed they took into account the shrink/swell problems that would come from such a high-volume change material like the weathered material. The weathered chalk is a very stiff to hard material (probably 2 to 3 ksf-kips per square foot) so it wouldn't need any casing to keep hole integrity. That the material is stiff to hard chalk is good because the contractor doesn't have to use drilling mud nor water, thus be able to free fall the concrete into the hole and not have to use a tremie.
What the contractor needs to do, after pumping the water out of the hole, is bring the drilling rig back in and drill about another 2 feet. That should take out the rest of the contaminated material and make for good hole integrity....and be sure they have the cages ready and the concrete already ordered.
This looks like a case of the contractor being penny-wise and pound-stupid.
The soil underlying DWS is Demopolis chalk, weathered overlying unweathered. I would estimate the weathered material was about 15-20 feet deep (from my memory of the holes for the bridges drilled for Hwy 25 and 82 in the late '90's). That the holes were 40 feet deep showed they took into account the shrink/swell problems that would come from such a high-volume change material like the weathered material. The weathered chalk is a very stiff to hard material (probably 2 to 3 ksf-kips per square foot) so it wouldn't need any casing to keep hole integrity. That the material is stiff to hard chalk is good because the contractor doesn't have to use drilling mud nor water, thus be able to free fall the concrete into the hole and not have to use a tremie.
What the contractor needs to do, after pumping the water out of the hole, is bring the drilling rig back in and drill about another 2 feet. That should take out the rest of the contaminated material and make for good hole integrity....and be sure they have the cages ready and the concrete already ordered.
This looks like a case of the contractor being penny-wise and pound-stupid.