Sasago Tunnel: Ceiling Panels Were Welded Together

Reason unknown.

I thought that at least Japan's civil engineering was still solid. Wrong.

Sankei Shinbun, quoting Kyodo News (12/5/2012):

トンネル天井板は溶接　広範囲崩落の要因か

Ceiling panels of the tunnel were welded together, may have contributed to a large section collapse

９人が死亡、２人が重軽傷を負った山梨県の中央自動車道笹子トンネル崩落事故で、落下した天井板は鉄筋で溶接され、隣接する天井板とつながっていたことが５日、中央道を管理する中日本高速道路への取材で分かった。

9 people died and 2 people suffered injuries in the collapse of [ceiling panels in] Sasago Tunnel on Chuo Expressway in Yamanashi Prefecture. It was revealed on December 5 that the ceiling panels that fell were welded together using rebar.

　崩落は長さ約１３０メートルにわたって起きており、中日本高速はつながっていたことが要因となった可能性を認めている。県警は、現場検証に同行した専門家らの意見を聴き、押収資料を分析するなどして崩落が広範囲にわたった原因を調べる。

The collapsed section is 130 meters long, and Central Nippon Expressway Company is admitting the possibility that the connected ceiling panels contributed to the collapse. The prefectural police will conduct the investigation by taking with the experts who accompanied the inspection of the scene of the accident and analyzing the documents seized from

　中日本高速によると、天井板はコンクリート製で、幅５メートル、奥行き１・２メートル、厚さ８、９センチ。１枚の重さは約１・２トンで、隣接する天井板とはわずかな隙間があるが、それを埋めるように金属で溶接されていた。

According to Central Nippon Expressway, the 5m x 1.2m x 8.9 centimeter ceiling panels are made of concrete, weighing about 1.2 tonne each. There is a small gap in between the ceiling panels, but the gap was filled with metal [rebar] and welded.

　中日本高速は「実際の壊れ方はまだ分からないが、１カ所が落ちてそれに引きずられた可能性も否定できない」としている。

Central Nippon Expressway says, "We still don't know how it actually collapsed, but we cannot deny the possibility that one segment fell, taking the other segments with it."

I thought, "How can you weld a concrete panel?" Looking at the video of FNN News below, the concrete ceiling panels seem to be covered by metal casings.

From FNN News Youtube channel (12/6/2012):

Neither Central Nippon Expressway Company nor the Yamanashi prefectural police has the detailed information or photos or the video regarding this accident available at their websites. I guess they have no intention of learning from the Fukushima nuclear accident when it comes to timely disclosure of information to the general public.

Tweet

Sasago Tunnel Accident: "No Corrosion of Bolts, Only Some Rust, Ceiling Intact", Says Yomiuri, But NHK Says "Some Bolts Corroded, Cracked"

Information on the accident is dribbling out via the media, not directly through the tunnel operator NEXCO Central, whose website has zero information on the accident other than their "Sorry for the accident victims" message, or the ministry in charge (Ministry of Land, Infrastructure, Transport and Tourism) which set up an investigation committee made up of scholars and university professors (as if they had ever worked a day in construction).

First, from Yomiuri Shinbun (12/4/2012):

山梨県の中央自動車道・笹子トンネルの天井板崩落事故を受け、国土交通省の調査検討委員会が４日、崩落現場を視察し、初会合を開いた。

The Investigation committee of the Ministry of Land, Infrastructure, Transport and Tourism surveyed the accident location and met for the first time on December 4 after the Sasago Tunnel accident in Yamanashi Prefecture where the ceiling panels collapsed [killing 9 people].

調査委は、報道陣の取材に、抜け落ちたアンカーボルトに目立った腐食がなかったことなどを明らかにした。調査委では、抜け落ちた理由についてさらに詳細に調べる。

The committee revealed to the press that there was no noticeable corrosion on the anchor bolts that fell from the ceiling. The committee will further investigate in order to determine why the bolts fell.

視察は約１時間。落下したアンカーボルトの状態や、トンネル上部のコンクリートの状況を確認した。調査委によると、上部のコンクリートが大きく剥落した形跡はなく、アンカーボルトも一部さびなどがあったが、目立ったものではなかったという。

The survey lasted for about one hour. The committee members saw the anchor bolts that fell, and looked at the concrete ceiling of the tunnel. According to the committee, there was no evidence of large flaking of concrete, and while some anchor bolts showed some rusting, it was minor.

また調査委は、中日本高速道路会社社員から、これまで行ってきた点検の方法を確認。調査委では「社内のマニュアル通りに点検していたが、そのマニュアルが適切だったかは現段階では判断できない」としている。

The committee also confirmed the maintenance method with the Central Nippon Expressway Company. According to the committee, they were "conducting the maintenance according to the internal manual, but we cannot determine at this point whether the manual was appropriate."

As if there is only one manual. From my personal experience, they may have at least three manuals, one for the submission to the regulatory authority, one as the official company manual, one as the unofficial manual for the field workers. I wouldn't be surprised if there's yet another one, unofficial, oral manual handed down the workers who really know the situation.

However, NHK, reporting on the police investigation, says bolts were corroded and cracked (12/5/2012; part):

警察のこれまでの調べで、現場から天井板をつり下げるつり金具のボルトがトンネル上部の壁から抜け落ちているのが複数見つかったということです。

According to the police investigating the scene, there were multiple metal bolts that had fallen from the tunnel ceiling, which had been used to secure the metal bars that had suspended the ceiling panels.

ボルトは一部が腐食したり、割れたりしているということで、警察はボルトがどのように抜け落ちたか詳しく調べることにしています。

Some corrosion was found on the bolts, and some of them were found cracked, according to the police. They will further investigate how the bolts fell.

Does the Ministry of Land, Infrastructure, Transport and Tourism have the minutes of the expert committee meeting on December 4? Yes it does, sort of. The ministry's website has a "minute summary" that consists of seven short sentences. As to the accident, it has this to say:

２）事故の経緯
・事故の発生メカニズムについての議論がなされた

2) How the accident happened
- There was a discussion of how the accident happened.

You would think the government and the government experts have learned the lesson from the Fukushima accident - that information needs to be promptly and fully disclosed. So we have no choice but rely on the media, and muddle through.

Life is completely back to normal in Japan.

Tweet

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)

Tweet