# Tunnel boring machine

The world's largest machines

 Superlative tunnel boring machine: boring head with a diameter of 15 meters

How are tunnels constructed through the highest mountains of the Alps, under the English Channel, and under large cities? How do the longest train and highway tunnels in the world come into being with the help of tunnel boring machines? How are these 200 meter long and about 4,000 tons heavy machines controlled? And above all: How precisely do they have to be guided through the tunnel in order to reach their goal? That's what students find out in our tunnel boring machine experiment.

Tunnel boring machines are technologically very sophisticated. In major projects like the Gotthard Base Tunnel or the planned Brenner Base Tunnel, several counter-rotating tunnel boring machines advance from opposite sides of the mountain. But how can the two boring teams working deep down in the mountain manage to meet up precisely in the middle? This is where a geodetic guidance system comes into play to assure that only minimal deviations are allowed in the way to the place where the two tunnels connect. The precision now being achieved is amazing: for the 57 kilometer long Gotthard Base Tunnel the horizontal and vertical deviation at the meeting point was only one centimeter.

 Tunnel boring machines are drilling and securing more than 85 kilometers of the Gotthard Base Tunnel.
In our experiment the student team has to meet several requirements in order to achieve an equivalent precision:

 With "Geo-Daisy", the junior surveyors drill a tunnel.
Being able to imagine threedimensionally helps when working with various spatially aligned laser modules. And so does some team spirit, in order to work together to get the best possible result. If you also have the required sensitive touch to steer our tunnel boring machine "Geo-Daisy" along a given route, then there should be no problem with successfully meeting up. At several stations the model tunnel boring machine has to be positioned and oriented in the direction of the laser beam with the help of marked tracking points. Take care: just as in the real case, any imprecision will have consequences for how closely you meet up at the end of the route! If all the "junior surveyors" do a good job, the meeting point can be reached with millimeter accuracy.