What is being constructed? (See details).

It looks like they are building a block of homes near where I work. They are building houses all around the perimeter, but they did something I’ve never seen before in the center of the block.

They dug a hole about the size and depth of an Olympic swimming pool. Depth is somewhat tricky because I am eight floors up and it is very difficult to determine depth from this height.

Then they laid down black pipes about one or two feet in diameter. They laid these in parallel rows down the length of the hole. Then they covered the pipes over with dirt. Since then they have done nothing. The area is surrounded by that orange plastic warning fence stuff.

Any ideas?