How do I build an underground tunnel?

first off don't say I'm trying to flee the country or get out of jail, its all gonna be on my property. I want to build a tunnel about 8 feet tall, about 7 feet wide, 50 feet long, and 5-10 feet underground (that's 5-10 down then the 8 feet of the tunnel). I live in Florida (Orlando) and I don't want to hit the water table, so yeah id want to know if that'll happen in 18 feet of digging. But my most important question is, what do I use to support the tunnel? I'm talking about sealing this tight like bricks, cement, concrete, I know I'm gonna have to use timber to support it while I build it. I don't want any water seeping through into the tunnel because theirs going to be electricity for lighting in it. And tell me if I'll need to use support beams around in it other then the walls themselves. Cars well over a ton may drive over it, so it needs to be something absolutely safe that wont cave in, COST IS NOT A FACTOR HERE. Also any pointers on how I should dig or what I need or how many guys this will take? I appreciate it very very much.