>What do you do with all that dirt?

>... The Boring Company is investigating technologies that will recycle the earth into useful bricks to be used to build structures... These bricks can potentially be used as a portion of the tunnel lining itself, which is typically built from concrete. Since concrete production accounts for 4.5% of the world’s greenhouse gas emissions, earth bricks would reduce both environmental impact and tunneling costs.

I called it. :) https://news.ycombinator.com/item?id=14224261