Capitol Visitors Center

UNITED STATES - JANUARY 14: A crane working on the Capitol Visitors Center outside the Senate side, East Front of the U.S. Capitol pulls dirt out of a trench called the slurry process. The slurry process, first they excavate 6-8 feet to make room for cement guide walls, then they use a large crane to go down through the guide walls and remove the dirt, all the while pumping slurry into the hole, which acts as a stabilizer to prevent the 65+ foot trench from caving in on itself. The material is less dense than cement, so when they put the epoxy-coated steel cages into the trenches and pour cement into them, the slurry raises to the top. (Photo By Douglas Graham/Roll Call/Getty Images)