Here's another discussion about footers. This is from our old pal DJ, you remember him, right?
What the man in the photo is drilling into is typicially referred to in the construction industry as a "pile."
A pile is a vertical shaft made of concrete that is created by drilling a hole into the ground, putting a circular form inside the hole, and pouring concrete inside the form. It typically has reinforcing steel inside the concrete to make the pile stronger.
The purpose of a pile is to prevent the structure above it, in this case a roller coaster, from sinking.
In the construction of buildings, piles typically go deep enough to hit bedrock beneath the soil. However in the case of many coasters, which are lighter than buildings, the piles often do not need to go that deep. This all depends on the soil the ride is built on, which is the type of information a geotechnical engineer can tell you.
The large, flat holes in the ground that the workers are creating and filling with concrete and steel in other photos are called "spread footings." These serve the same purpose as a pile (i.e. to make sure a structure doesn't sink), but instead of going deep vertically to gather its support, a spread footing stays closer to the surface and depends mostly on the soil beneath it to support itself.
Each patch of soil has specific properties, and some can support more force (weight) per square foot than other soil. Once the engineer knows the properties of the soil, and how much force the ride puts on the ground, he can design a sufficient spread footing.
Just remember that without careful consideration of a roller coaster's foundation, the ride will likely start sinking in many areas soon after being built. This is why you often don't see much vertical construction early on when a ride is being built. The creators are making sure the ride doesn't sink for future park patrons to enjoy for years to come.
There's something quite likeable about engineers, isn't there? They may not be the flashiest individuals, but they're smart and they like to explain what it is they do.
And I'm surrounded by them! (Will has an Electrical Engineering degree from Notre Dame, his dad had an engineering degree from Purdue, and my oldest son is an EE/Math major at my husband/his dad's alma mater.) And then there are our pals at The Gravity Group.
I must admit, my eyes roll back in my head fairly often.
But it's always a learning experience.