Friday, February 19, 2010

How Japanese tunnels are built


Our new tunnel will shorten our drive down the river to Gotsu by a little more than 200 meters. Being straight the tunnel will also be more fuel efficient to drive. A rough calculation says that with present traffic density the fuel savings will have paid for the tunnel in only a few million years. Incidentally, that is my village to the left of the tunnel.


This is the machine that actually drills its way through the mountain. I was expecting to see a huge machine almost as big as the tunnel.... watched too many movies I guess! These smaller drill splay out at any angle.


The next stage is to put up steel arches and then a series of steel beams are driven into the mountain radiating out from the tunnel. Then the tunnel is coated in a thin layer of concrete.


The purpose of the steel beams is to stop the tunnel collapsing under the weight of the mountain, represented here in this demonstration by steel nuts.


Next a thick, waterproof, plastic membrane covers the inside of the tunnel followed by a frame of reinforcing rebar,


The final stage involves this huge machine on rails which is a movable form. Its used to pour the final inner walls of the tunnel.


  1. Very well researched and interesting. Are there any businesses to the right of the tunnel? My first worry was that some little mom and pop conbini would be put out of business by the tunnel. hhhhm. I encountered this sort of patter a lot around Shikoku. I usually choose to walk through the tunnel and risk it not having sidewalks than to walk a longer mountain road.

  2. There is only a few homes. Mostly round here the tunnels are to straighten the road rather than follow the windy river. After the tunnels the windy river roads are great for walking cos there is no traffic.

  3. Once again, great post. You never see this sort of thing on other sites, so well done. It always amazed me how many tunnels there are in Japan. Going up the coast from Sapporo to Mashike (which isn't that mountainous) we counted 14-15 tunnels.

    In Adelaide, we got excited to have one tunnel about 300m long (and it took about 3-4 years to make). The difference that comes when you do something all the time.

  4. On your map it looks as though that tunnel could become a new route for the river if it flooded and the level rose too high.Floods here in Eastern Australia of late have risen to amazing heights and inundated huge areas.Great post as usual.