In 2017 even Elon Musk talks about tunnel construction, but how did it all start?
Join me on a journey into the ancient world and together we will be a little smarter.
If anything should be unclear, please write a comment and I will gladly help.
You should know this about tunnel construction
The most important in tunnel construction is the measurement of the tunnel between the portals.
The measurement happens mostly above ground and must then be transferred to the underground.
Observance of the track guidance in the tunnel drive should be independent of the relied backup procedures or light hole methods.
Planning of the tunnel route
The simplest way to stake a tunnel overground is the “cross-straightening” straight-line procedure. This is not mentioned in ancient times, but because of its simplicity, it was very probably used.
For each portal (A and B) an escape rod is placed. Thereafter, two alignment point (A1 and B1) are also placed on the slopes. They are positioned in such a way that the escape alignment point and portal can be seen from each of the two escape rods on the opposite side of the mountain.
When this is done, then A1 from B1 is brought into a flight with A and then B1 from A1 to a flight with B.
This procedure is repeated until all four escape rods are aligned.
However, in the case of longer distances, a number of auxiliary points must be set, due to the visibility and rounding of the earth.
Track leveling of the portals
Next, the route is leveled and the height of the portals is set so that the tunnel has the desired slope. The type of transmission of the pre-stretching direction from the upper day to the lower surface depends on whether the tunnel is approached in the counter-project or by the light hole method.
Transfer of the route guidance
According to the above-ground planning of the tunnel bridge, this has to be implemented in the course of the construction work. If this happens in the counter-procedure, the tunnel is driven from both portals. In order to transfer the trail laid out in the upper days to the underground, the flight must be extended in front of the portals via two further fixed points.
If there is a valley opposite the portal, the fixed point is laid out in such a way that it can be seen from the inside of the tunnel as long as possible.
Examples of antique tunnel constructions
Street tunnel of Via Flaminia
The Via Flaminia, built in 220 or 223 BC by Gaius Flaminius, was the most important road connection between Rome and the Adriatic. When the road under Augustus was expanded, a rocky nose with an 8 meter long and 3-meter wide tunnel crossed the valley of the river Candigliano, on the Fluro Pass.
Under Vespasian a new tunnel of 37 meters length, a building history can be reconstructed.
After the two portals had been marked on the same level, a horizontal search was started in the counter-project.
Subsequently, the ridge was laid higher in the southern section, and the bottom was sunk downwards from south to north over the course of the tunnel to a slope of 10%.
This gradient was necessary to allow the tunnel to be integrated into the Augustan route. In the course of modern road construction, the steep gradient was reduced by placing the road in the southern part lower and in the north higher. The tunnel is still used today.
Work in process