Don't they use super thick concrete like this for nuclear reactors? You'd think they would be able to just use a crane to drop something like this and the thickness and weight would be enough to damp the well.
The ocean floor is a mixture of mud and ooze. The pressure from the well will just push this out of the way and continue to leak.
They could but some for reason they have decided to try using hair to stop the flow... The reason they don't is basically because if you stick a big chunk of concrete into the hole the oil would still be trying to leak and so the pressure would build up. This means you could end up with a giant concrete slap propelled from the hole, which is never good. What they should do it create lots of smaller leaks and collect the oil from those.
That was kind of the basic concept of the first cap they used. The problem was a large percentage of the oil leaking was actually methane. When the methane mixes with water it forms methane clathrate which plugged up the cap. On top of that methane clathrate has a density less than that of water and caused the cap to float.
