From 3D imaging, to computer-assisted boring, to the material lining the walls, this tunnel lays claim to a lot of firsts. For instance, that material is a new hybrid of concrete and polymer fibers, to resist fracturing.
The machine doing the drilling, the Alpine 1 "road header", is so specialized, there are only two in all the United States, and both are working on this project. Every day, it's programmed to excavate a precise profile.
Up inside the cab,that profile will appear on a computer screen. And the operator has to stay within the programmed bounds, or the computer lets him know. It's a little like a video game. There's even a joystick. But how does it know where to go? There's no GPS inside a tunnel. But there is a laser bat on the ceiling, which is the starting point for everything. It tells all the machines where they are and talks to other lasers. One of them is the Dibit. The Dibit scans the shape of the tunnel and the type of rock every step of the way, with camera and laser beam.
That laser beam is invisible to humans, so envision a laser pointer. It shoots a tiny spot 24,000 times a second, about 5mm resolution. And from that it builds a 3D model of the tunnel.
This is the first time 3D visualization is being used in this way. It reveals faults and fissures and color codes the hardness of rock. That's critical, because this is a highly unusual project. The same shifting geology that so often makes the highway outside impassible, challenges the engineers to revise their plans in midstream every day.
"The computers, the models, will never tell you everything, until you actually see the ground out here. That's where we adjust, and that's where people become valuable," said Ivan Ramirez, Caltrans senior engineer.
In other words, computers might have better tunnel vision, but humans are still better at boring things.
------- Links -------