This gives workers a starting point. In order to prep the mountain for the tunnels, workers first made a vertical cut down the side of the mountain. A giant machine called a roadheader is used to drill through the mountain. Sometimes the roadheader would hit rock that was too hard to bore through. In fact rock on the Halawa side of the Ko'olaus is actually softer than rock on the Haiku side.
Plastic pipe is inserted into the holes and explosives are inserted into the pipes.
The rock is blown apart and the rubble is cleared away. Finally, workers spray the bare rock with a mixture of concrete and steel fibers to hold it in place. Even with all of the drilling and blasting, the work is not very hazardous. As long as everything is done correctly, no one should get hurt. The giant slits on the tops of the tunnel entrances are not walkways, but rather ventilation shafts for the 4-10 foot high fans that allow air to move through the tunnels.