Development of a tunnel excavation system using 3D scanning and projection mapping

In mountain tunneling, the excavation positions—i.e., crown, side, and invert— are managed to reduce muck excavation for disposal and concrete for placing. Invert is the bottom part of a tunnel, whose function, among... [ view full abstract ]

In mountain tunneling, the excavation positions—i.e., crown, side, and invert— are managed to reduce muck excavation for disposal and concrete for placing. Invert is the bottom part of a tunnel, whose function, among others, is to prevent

・Heaving.

・Ground degradation by repeated load.

・Subsidence of covering concrete.

・Displacement of side wall.

In the current practice of excavation management, the crown, and side parts excavation management are verified using a marked rod, while the invert part is verified using a string level and marked rod, or a ruler shaped cross-section of the tunnel. There are, however, some problems in this method, some of which we enumerate below:

・It is time-consuming.

・Causes delays because of traffic of heavy machines and cars when a string level is used.

・More manpower is needed.

・Risk of injuries and accidents.

In order to save labor, reduce manpower, and improve safety, we develop a mountain tunnel excavation system. This system combines 3D scanning and a knowledge of projection mapping. It comprises a 3D scanner measurement and projector (together, hereinafter, called "device") for tunnel shape measurement and picture projection, respectively; a personal computer (PC) for picture creation; and hemisphere markers for the estimation of the device position. The procedure of this system is described below.

1. The device is installed near the excavation area, and the two markers are installed at points of known coordinate values.

2. The tunnel shape is measured using the 3D scanner.

3. The orientation of the device is estimated using the measurement result from the 3D scanner.

4. The relative coordinate values of the two installed markers are derived using measured data from the 3D scanner on the surface of the markers and the least squares method. The self-position of the device is derived.

5. The PC is used to decide which of the scanned points needs to be excavated by comparing the scanned data and design data of the tunnel.

6. A picture is created of the scanned area decided for the excavation.

7. The picture is projected onto the excavation area using the projector.

8. An operator of a heavy machine excavates while looking at the projected image.

The time it takes from scanning to projecting the picture is 1 min. We demonstrated this by conducting an experiment at an invert excavation area for a mountain tunnel under construction. We report the results of the experiment and the practicability of this system.