Why do I care about tunneling?

Tunnels have a long history of being mysterious secrets, which are hidden away for hundreds or thousands of years as water supply systems or secret connections under existing cities. Studying tunnels requires me to go beyond the visible structure. Darkness and hard labor, together with engineering strategy and new machinery give me a mix of adventure and know-how. It is fascinating to create a tunnel in the ground, no one ever sees behind it, most parts of a tunnel are invisible to the normal eye. And yet, building a tunnel takes so much.

This passion of me is something I want to give on. So it came that I was able to give a lecture about tunneling at Oregon State University (OSU), where I study right now for my doctorate in geotechnical engineering.

I am going to use my blog here to answer the questions I got during the lecture. Some are going to be answered now, some in later posts.

• How long is a tunnel boring machine (TBM)?

• The TBM itself can be around 25 m (80 ft) long; however, the backup system to manage all the logistics for the tunnel excavation and support installation can be up to 150 m (500 ft) or more.

• How do you deal with extreme seasonal whether changes (-30°F to +80°F and icing issues in the portals)?

• The problem of extreme whether changes requires good construction materials and workmanship. Temperature changes must be considered during the design phase.

• Old tunnels can show icing at the walls close to the portals which could mean cracks somewhere in the wall so the water from the rock or surrounding ground can travel through the tunnel structure. If the leak is not extreme, you monitor it every year or every several years and then decide what to do.

• In case of a new tunnel with icing close to the portals, you see where the water comes into the tunnel and when appropriate or necessary, those tunnel areas can be injected and sealed, especially when the tunnel lining is made out of reinforced concrete.

• During fires, do they cut the ventilation to reduce oxygen?

• No. In a tunnel a special ventilation is activated during a fire to suck the smoke away from the fire and people can rescue them selves to the next emergency exit without having to go through deadly smoke. 

• Because the tunnel is a closed tube, the biggest problem is the extreme heat which could result into the collapse of the tunnel structure which is dangerous for the rescue groups and fire fighters.

• Ventilation and heat have to be considered in the design of the tunnel structure.