Book 25, Question 1
What happens on a building site before the first floor goes up?
Before building a skyscraper, engineers drill test holes to learn what the soil and rock are like.
Then crews dig a giant hole and haul away the dirt. Next, they build the foundation. Many towers stand on huge concrete columns called piles that reach deep into the ground, so the weight of the tower is held safely. Only after this hidden work can the building start to rise.