Hey,
These tunnels are nothing new. In fact, it appears that you are in the "upper" tunnels or utility tunnels....the ones people are in and out of all the time. The really interesting ones you have to access in the oldest parts of campus look like fallout shelters or old ice cellars. Now they are used to store extremely old equipment from the 30s and 40s. There is some really interesting stuff down there. Although I didn't steal anything for the fear of being expelled my buddy Justin (who found them working on the fiber networks) got some decent lab equipment despite it being 60+ years old. You can get to them from the main building (the tower) but you will need someone with a utility key for the elevator and some official looking nametags (if there is anyone down there they will know what you are doing as the "looking for the registrar's office" excuse is not going to work. Luckily, UT hires all sorts of contractors for everything so any kind of official looking nametag should do the trick. It is said that a full 25% of UTs square footage can be found underground. If you get a chance, you should check out the tokamak fusion reactor under the math building. You don't even have to sneak in--they hold tours.