I just saw one of the best pieces of documentary filmmaking ever. I'm watching the Science Channel show "Building the Ultimate", an episode about a highway across northern Greece. We're about five or ten minutes in; the narrator has just mentioned that building the highway will require about 50 miles of tunneling.
Scene: images of heavy equipment digging in a tunnel.
... no matter how much planning and preparation you put in, there's always the unexpected.
Unidentified male British voice:
Before we start a tunnel, we very often don't know in detail what we're going to tunnel through.
Scene: Healthy looking middle aged white man in Engineer's Field Uniform (khakis, oxford blue dress shirt open at the collar, sleeves rolled up), standing on in tall, brown grass on mixed vegetation, obviously Mediterranean hillside. This is the man whose voice has been speaking, identified in a caption as Tom Hughes, Deputy Project Manager, Western Region.
So we have surprises along the way.
Camera pulls back, revealing raw earth falling away vertically just in front of him.
This is the result of one such surprise.
Camera continues to pull back as he speaks.
It's a surface depression, which has formed as a result of tunneling operations which are taking place some 75 to 80 meters beneath us. It's the result of the disturbance of a solution cavity. A solution cavity is a geological feature formed over many thousands of years, found mainly in limestones...
The camera finally stops pulling back. Mr Hughes is now tiny, occupying perhaps one tenth the height of the screen. The vertical fall below him is two or three times his height. We see the left edge of the surface depression at the left edge of the screen. The right and bottom edges are offscreen, but in our view, the left edge has not yet begun to curve inward and the top edge has not yet begun to curve down. This suggests we are looking at its upper left quadrant. It's huge. Assuming Mr Hughes is six feet tall, it's easily 120 feet in diameter. Camera holds position as he continues.
... and is the result of the dissolution of the limestone material by water percolating through the limestone. When we tunnel beneath it....
Camera shifts to a view down into the depression, panning across it. It looks much deeper from this angle.
... we remove the support at the base of, in this case, a vertical cavity. And because we've taken away the support...
Camera shifts back to the view of the tiny Mr. Hughes standing at the edge of the cavity.
... the whole lot drops. Into the tunnel. The result is [pause] this.
Even though one of my very best friends was Course XII, I don't know much geology. But I will never, ever forget what a solution cavity is. Or what one can do. (In case you are wondering, as I was: no, there were no fatalities.)
The episode has other cute moments, lots of brief scenes of engineers talking enthusiastically about their work, though nothing so dramatic as the solution cavity.
My favorite is a demo given by an engineer in the field, standing in the middle of the not yet paved road bed, two tunnels in the background (the road is a double carriageway), at a waist-high table presumably normally used for looking at blueprints. He's very fidgety, clearly nervous about being on camera. "What I've got here is two piles of sand. This one" (handwave stage left) "has got four layers of reinforcement similar to this in it." He waves a paper-plate sized disk of material he's been fidgeting with all along. It's translucent and looks rather like white nylon window screen. "And this pile is unreinforced. Now I'm going to load these piles and demonstrate the difference that this reinforcement makes." He reaches out of view stage left and brings into a view a 2-liter water bottle full of sand, which he sets on what appears to be a coaster atop the unreinforced pile of sand. "If I load this one" — it sinks in immediately, before he's even done letting go — "you can see that it fails, and I can cause it to fail" — pushes down on the bottle cap with one finger, sinking it about twice as far. — "very easily." He picks up the bottle and moves the coaster to the other pile. "Now, when I load this one" — action follows words, pulling his hands back after setting the bottle down to fidget with his belt loops — "it doesn't fail. Even when I press it" — with this, he cups both hands over the top of the bottle and leans forward — no matter how much pressure I put on, I can't fail it." He then grunts as he poshes down hard, and pushes himself back into an upright position. The reinforced sand pile did not deform. I'm a believer.