Why Would They Do That?

I've watched a construction project from our balcony since moving back here in 2009. The work on the right is building an apartment tower that will be about fifty stories tall. But, the work on the left looks like a very expensive make-work project.

  I couldn't imagine the cost of this machine digging about 80 feet down, hauling out the soil, only for the backhoe in the foreground to dump the soil back down the hole before the steel sheathing is pulled out. They would move over a few feet and repeat the process.
Then one day I saw the backhoe mixing some powder into the soil before dumping it back down the hole. No doubt that's ground solidifier, to help prevent liquefaction, the phenomenon of soil sinking and water rushing to the surface. 

I suspect that also explains the unusual sight of this barge with the gigantic drill and the large cement hopper. The drill burrows under the river, and as it is pulled up, cement is pumped out of holes near the drill bit to mix with the soil and make it solid.

 

This kind of thing is usually done to prepare the ground for constructing a building. In our case, I think it's firming up the riverbed so we don't have more subsidence like we had after the March 11 earthquake. You'll find that post entitled "We are Sinking" on March 30. Perhaps they're concerned about our reclaimed island shifting sideways into the river, so they're strengthening the riverbed to prevent it. We appreciate the effort, since people in Urayasu in Chiba still don't have water or gas because of all the liquefaction of the ground, not to mention leaning homes and manholes five feet above the road!