Failure Knowledge Database / 100 Selected Cases

Concrete flaking in a Shinkansen tunnel of West Japan Railway Co.
[ June 27th, 1999・October 9th, 1999, Fukuoka Prefecture ]Masahiko KUNISHIMA・Yukihiro ISHIHARA ( Note 1 )In June, 1999, concrete in the Fukuoka tunnel between Kokura and Hakata in JR
Sanyo Shinkansen line flaked off. The flake hit a Hikari Shinkansen train running in
the tunnel directly, and the roof of rolling stock was torn up within about 16m long and1m wide, and part of the pantograph was damaged. The Hikari Shinkansen train
stopped suddenly, since the power transmission stopped near the tunnel exit. Luckily,
no one was injured, but suspension and delay of trains of this section arose one after
another from the power cut in both up and down tracks.
Because of this accident, West Japan Railway Co. checked all tunnels of Sanyo
Shinkansen line and made the safety announcement. But in October, the same year, it
was found that about 226 kg concrete mass, which broke into 5 pieces, had fallen by theline of the Kitakyushu tunnel in the same section. West Japan Railway Co. stopped theSanyo Shinkansen line, and about 10 hours were taken for all lines to restart.
By a series of these events, the safe image of the Shinkansen line was shaken.
１．EventIn June, 1999, concrete in the Fukuoka
tunnel between Kokura and Hakata in JR
Sanyo Shinkansen line flaked off and the flake
hit a Hikari Shinkansen train running in thetunnel directly. And it was found that concrete
mass had fallen in the Kitakyushu tunnel inthe same section. (Photograph of the site isshown in Figure 1.) Since 1996, many cases of
the concrete piece falling from viaduct had

Figure 1. Kitakyushu tunnel flaking site

been reported, and it turned out that concrete(Source: Chugoku newspaper)

structures of Sanyo Shinkansen line had problems with safety and durability.
２．Course
At about 9:25 a.m., on June 27th, 1999, concrete in the Fukuoka tunnel between
Kokura and Hakata in JR Sanyo Shinkansen line flaked off. The flake hit a Hikari
Shinkansen train running in the tunnel directly, and the roof of coach 9 was torn up
within about 16m long and 1m wide, and the pantograph of coach 12 and 10 was1

Failure Knowledge Database / 100 Selected Cases

damaged. Luckily, no one was injured, but the Hikari Shinkansen train stopped
suddenly near the tunnel exit because of the power cut. Suspension and delay of trainsof this section arose one after another from the power cut. By 1:30 p.m., both the up anddown tracks restarted.
At about 4:10 p.m., on October 9th, the same year, it was found that the concrete mass(334cm wide, 40cm deep, 15cm high, and about 226kg in gross weight), which broke into
5 pieces, had fallen by the line of the Kitakyushu tunnel in the same section. WestJapan Railway Co. canceled the operation of the Shin-Osaka-Hakata section, andrestarted the operation of the Shin-Osaka-Hiroshima section by 9 a.m., and that of theHiroshima- Hakata section by 4 p.m... This had an influence on about 62000 persons
including vacationists on what was the first day of 3 straight holidays.
３．CauseThe cause of the Fukuoka tunnel accident was the inconsecutive plane of the concrete,
which is called cold joint (CJ).（The figure which shows the outline of the accident isshown in Figure 2.）It is necessary to pour concrete into a form divided into divisions
with the restrictions such as lateral pressure of mold, assembly of reinforced steel,temperature rise of mass concrete, technical constraint, and the quantity of the concrete
which can be poured in one day, etc.. In this case, the condensation of the concrete
poured in advance advances, and a plane of discontinuity occurs between old concreteand new concrete. Throughout construction, curing, and use, the crack was generated in
the inside of the CJ, and it developed, and it seemed to cause the flaking.
In the Kitakyushu tunnel, the method called "flying arch method" was adopted. In thismethod, firstly the arch concrete was constructed, a protuberant pouring mouth wasequipped between the mould of the side wall and the arch concrete, and the side wallconcrete was poured later. This protuberant pouring mouth was not removed after
completion of the tunnel. For some reasons such as subsidence of the side wall, thecrack between the projection and the side wall was generated. Then, the crackdeveloped further by water leak, temperature change, train vibrations, etc. over time,and it finally fell by the dead weight. The figure which shows the outline of the accident
in the Kitakyushu tunnel is shown in Figure 3.

2

Failure Knowledge Database / 100 Selected Cases

Figure 2. The outline of Fukuoka tunnel accident

Figure 3. The outline of Kitakyushu tunnel accident(Source: Nikkei construction)(Source: Nikkei construction)

４．Immediate Action
The accident on June 27th resulted from a cold joint (CJ), which West Japan Railway
Co. did not make to be one of check items then. West Japan Railway Co. checked CJ ofall 142 tunnels of Sanyo Shinkansen line (they extended for about 280km.) by carryingout a hammering test. CJ was found at no less than 2049 places in 93 tunnels. It carriedout temporary measures such as removal of the bad part byhitting, and the safety announcement was made in August
after the check.
On October 9th, after about 3 months, as if mocked theinspection on CJ, the protuberance in tunnel side wall,called placing mouth collapsed. West Japan Railway Co.,
which considered the situation serious by these 2 accidents"assumed all situations" for prevention of recurrence of theaccident, and from October 25th, carried out the bigger
inspection than ever with its deadline on December 15th toall 142 tunnels. From November 8th, a total of 9 trains inboth up and down tracks of the Hiroshima- Hakata section

Figure 4. Hammering test

were canceled or partly canceled, the last train was run at an （Source: Chugoku newspaper)
earlier time, and the work time of the same section was extended by about one hour.
Since the whole line opening (March, 1975), there was a complete inspection involving asuspension of operations for the first time. The photograph of Figure 4. shows the aspect3Failure Knowledge Database / 100 Selected Casesof the hammering test which was opened on November 13th to public by West Japan
Railway Co. which did the whole inspection because of the accident of the Kitakyushu
tunnel.
５．Countermeasure
Since West Japan Railway Co. had successive concrete piece flaking accidents, while it
carried out a review of inspection periods, inspection methods, criteria, and repair
method of tunnel, viaduct and the like, it promoted the introduction of the accreditation
system in the repair work and positive introductions of the results of the newtechnology development, etc., and it tackled the improvement of the maintenancesystem.
On the other hand, one opinion is that the investigation and analysis andcountermeasure from the impartial standpoint should be made possible by establishingan accident investigation organization independent of the project-implementing body,and another opinion is that the Shinkansen is an infrastructure important to thecountry, the maintenance of it should not be entrusted only to JR, and it is necessary forthe country to tackle the maintenance as a national project which has priority over theother public works. And, there is an opinion that a series of inspection and repair aresuperficial, and it may not become a drastic solution to the problem including thedegradation of the concrete inside.
The new technology introduced into the tunnel maintenance① Tunnel Maintenance System (TuMaS)
The Results of the whole safety inspection of thetunnels in 1999 have been stored into a data base, andthis has become the system with mobile function thatmakes quick and easy update, retrieval and editing ofrepair history and transformation, etc...
② Tunnel lining surface inspection system (SATUZO)
By irradiating lining surface with laser and detecting

Figure 5. Inspection by SATUZO

intensity of the reflected light, the system can measure(Source: West Japan Railway Co)

the crack. This is a system which is a remarkable improvement of speed and precision ofmeasurement over those currently in use, and it aims at automated inspection in thefuture, and possesses the function of automatic detection of the crack (Figure 5.).
③ Others
In addition, there are inspection techniques under improvement directed towards the4Failure Knowledge Database / 100 Selected Cases

practical use and new technology about the viaduct maintenance, etc.
６．Generalization
Though these 2 accidents did not lead to the human injuries, because they were theaccidents involving the Shinkansen, which transports large passengers at a high speed,
there was the sufficient possibility in which the great damage could happen, and theinterest of the nation was focused on the way of safety management of West Japan
Railway Co... In addition to the technical problem of construction technology andmaintenance technology, a makeshift or ex post facto monitoring management attitude
came to light. The effort which prevents generation and recurrence of accident by
reexamining these problems has been made.
７．Knowledge
・It is necessary that the research institute sufficiently recognizes the mechanism(neutralization and alkali-aggregate reaction, etc.) in which concrete structure
deteriorates and copes technically with it.
・It is necessary to examine the solution to problems of concrete construction, such as
design of appropriate pouring methods and management of the site process.
・From the viewpoint of proposal and evaluation of new maintenance techniques, inaddition to technical aspects such as the mechanization of inspection process, anapproach from the political side that management systems and management ideas arereexamined is also necessary.
・In order to obtain the trust of the user, the attitude of "attaching greater importance tosafety than to management" is important and the effort, which the user doesn’t notice,for previously preventing accidents is necessary.
・About infrastructure which is scheduled to be constructed, considering utilizing theinfrastructure for a long time into the future, it is necessary to make designs which
consider a balance of maintenance costs and initial costs.
８．BackgroundThe background factors which caused the developing early deterioration of concrete tobecome the social problem from 1980's, were rush work, execution defect with it, andthe use of sea sand because of material shortage, etc..
In March, 1975, Sanyo Shinkansen was all opened for use, but the opening was 3
months behind schedule, and the situation was that the construction period could not beextended any longer. In addition, the oil crisis came, and the rushed work was done

5

Failure Knowledge Database / 100 Selected Cases

when the material shortage happened, in addition to a manpower shortage because of
the construction rush. It was not strange even if the work accuracy was made little of.
This brought about execution defect like CJ, which became a cause of the Fukuoka
tunnel accident.
At the end of the high-growth period, the sea sand, which was cheap and considered to
be inexhaustible attracted attention in the Chugoku district, which was not blessedwith good river sand, and much sea sand was also used for Sanyo Shinkansen. Seasand promotes corrosion of steel and alkali-aggregate reaction, if it has not been
desalinized beforehand. Some ready mixed concrete traders said that it was unusual touse correctly washed sea sand in those days, when rush work was forced.

The yearwhen the Ministry of Construction in those days gave an official notice to request thecompleteness of desalinization was 1977, 2 years after the whole opening of Sanyo
Shinkansen.
９．On the SideIn the television image after the accident-generation, the work situation in which theinspector who looked up and opened his mouth during the hammering test of theconcrete wall in the tunnel by hammer was broadcasted many times, and the society’s
trust for the civil engineering technology lowered.

As a result, this case can be said tobe one of the motives for the implementation of automatic measurement by themechanization.
＜Reference＞
Koei forum No.9th/2001.1"Concrete in danger" by KOBAYASHI Kazusuke, Iwanami Shinsho"Concrete technology" by KOBAYASHI Kazusuke, Morikita Shuppan
Chugoku newspaper http://www.chugoku-np.co.jp/
Nikkei construction
Nihon Keizai newspaper.
West Japan Railway Co. http://www.westjr.co.jp/ReNEWAL NEWS http://www.renewal-news.com/(Note 1) Department of Civil Engineering, Faculty of Engineering, the Univ. of Tokyo

6