Sasago Tunnel Accident: Concrete Ceiling Panels Fell When the 35-Year-Old Metal Bolts Securing the Panels Fell Off from the Tunnel Ceiling

This is the silliest design I've ever seen. But then I'm no engineer.

9 people were killed when the concrete ceiling panels in Sasago Tunnel in Yamanashi Prefecture suddenly caved and fell on the motorists who happened to be in the tunnel.

The media reports try to explain how the ceiling panels were secured by metal brackets, no, they were hanging from the ceiling, oh wait, no they were attached to the dividing wall in the middle, no they were secured by metal bolts. I guess the reporters aren't engineers either.

I finally found this drawing which seems to be more or less accurate.

From the news site "Iza":

Since the tunnel opened in 1977, there has been no maintenance, no testing of the bolts that secure and hang the concrete ceiling panels (1.2 tonne a piece). There is no record of the bolts ever replaced. All they have done every five years is visual inspection. Why? Because physical inspection was not required by law, and since the bolts are anchored at the highest part of the tunnel they are inaccessible.

After I tweeted I wanted to see the detailed diagram of the tunnel, my twitter followers sent me the graphics that show how the bolts and metal suspensions were attached to the concrete panel.

16 bolts, 1.6 centimeter in diameter and 23 centimeters long, secures the metal plate to the ceiling, using chemical anchor. The metal plate secures the 5.3-meter long metal bar that is connected to another metal plate securing two concrete panels, each weighing 1.2 tonnes and measuring 5 meters x 1.2 meters x 8 centimeters (thick). The middle divider is not connected to the ceiling, but the purpose seems to be to secure the metal bar that suspends the ceiling panels. (The image is from Tokyo Shinbun.)

Now, why did they need this strange ad-hoc-looking structure? (It is not actually ad-hoc, as this structure was in place when the tunnel opened for business in 1977.) It turned out that the air in the tunnel tended to stagnate, and with heavy traffic with motorists having to sit in the tunnel for an extended period of time the risk of carbon monoxide poisoning was high. So they needed a structure that would allow effective air flow. So they decided to create air ducts by dividing the tunnel by concrete panels suspended from the ceiling by metal bars which would be supported by concrete divider wall that would separate the duct space in two, and the metal gars would be bolted to the ceiling.

Who were the general contractors who did this job? I looked all over, and there are only rumors. No major news outlets mention the names of the general contractors.

Rumors or no rumors, share prices of Japan's 1st-tier and second-tier general contractors jumped in the stock market in Japan on Monday. Kumagai-gumi, one of the most skilled contractors in tunnels, jumped more than 10 percent.

Why? Because the market thinks it is now extremely certain that the Japanese government will spend another borrowed fortune on public works, in response to citizens' fear and outrage that their infrastructure has deteriorated rapidly. As one of my followers said, it's not that the top-tier general contractors are good at maintenance (they aren't).

Well, 35 years of deferred maintenance does wonders. Like generating fat profits for general contractors who will throw work down their construction subcontractor pyramids. Dango anyone?

(H/T Kontan_Bigcat, Morimorikids, dr_masa_, 110rin, mwuema)

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