Causes and Lessons of the Wachi Dam Gate Failure Accident
Causes and Lessons of the Wachi Dam Gate Failure Accident
Asked to Chat GPT No. 017
Questioner: Isao Nagayama
Respondent: Chat GPT
[Question]
The Wachi Dam gate failure accident that occurred in July 1967 was highly significant in that the government admitted the cause lay in a design flaw rather than a construction defect. Please explain the process by which such a conclusion was reached.
[Answer]
1. Overview of the accident and initial views
This accident occurred on July 2, 1967, at the recently completed Wachi Dam (dam height 25 m), when one of the four gates suddenly failed, causing 500 m3/s of water to flow out and resulting in the death of one angler downstream. However, the Ministry of Construction's Wakayama Construction Office had found no issues during the dam's final inspection, and the office director stated to the press after the accident that "there were no problems during the inspection." Furthermore, Professor Yasuo Ishihara of the Disaster Prevention Research Institute at Kyoto University (hereinafter referred to as the Kyoto University DPRI) also stated to the press, "This type of dam has been around for a long time, and a design error is unlikely. I believe the cause is poor workmanship during construction."
2. Establishment of the Accident Investigation Committee
This accident was also taken up in the National Diet. Initially, the Ministry of Construction testified that "construction errors and inspection deficiencies are considered the cause," but it was decided in the Diet to establish an accident investigation committee to clarify the cause. Similar opinions were also expressed by experts (scholars).
Therefore, the Ministry of Construction and the Ministry of International Trade and Industry established the "Wachi Dam Gate Accident Technical Investigation Committee" to investigate the cause of the accident. Professor Katsumasa Yano of the Kyoto University DPRI was appointed as the chairman.
This committee was unusual for a government-established committee in that the Kyoto University DPRI played a central role in the proceedings. Furthermore, the on-site investigation and accident analysis were also led by the Kyoto University DPRI.
3. Scientific analysis and investigation of the cause
Initially, the government stated to the committee that construction errors and deficiencies in the final inspection were the cause of the accident, but as the committee's on-site investigation and structural analysis of the gate progressed, it became clear that construction defects alone could not explain the gate failure. Finally, a report was compiled stating that buckling failure occurred due to insufficient strength of the gate support pillars, which led to the failure accident.
4. Administrative response to the committee's conclusions
When the committee's final report revealed that the cause of the Wachi Dam gate failure was a design error, it was decided in the Diet to conduct a nationwide simultaneous inspection of dams of the same type and to revise technical standards as a measure to prevent similar accidents. Consequently, the Ministry of Construction conducted a nationwide inspection of dams and implemented reinforcement work where necessary. Design standards were also reviewed.
5. Further research into the causes of the gate failure accident
The investigation into the cause of the Wachi Dam gate failure and the subsequent response are as described above, but it is highly noteworthy that the scientific investigation into the cause of the accident was led by a university (academic research institution) rather than the government (administrative agency). This led to the identification of the true cause of the accident.
Furthermore, universities have continued to conduct additional research on the accident since then. According to the latest research, it has become clear that dynamic loads and gate vibrations caused by water flow fluctuations during gate operation may have been significantly involved in the failure. In other words, this indicates that the official conclusion at the time of the accident did not completely clarify the cause. This suggests that even if an official conclusion is reached, it is necessary to review it as needed in accordance with the progress of academic knowledge for the sake of technological development and safety improvement.
6. Summary
The Wachi Dam gate failure accident is a valuable case study that illustrates the difficulty of ensuring safety in civil engineering facilities. As is clear from this, design standards are not absolute and must be reviewed as needed in line with scientific progress. If one neglects this and treats technical standards as absolute, there is a danger of blaming the causes of accidents on construction or inspection errors. However, science and technology can also make mistakes. The Wachi Dam gate failure accident must be deeply remembered as a valuable case study that clearly demonstrates this.
*** Author's Comments ***
The following is the content of the Asahi Shimbun report at the time (see Figure 2).
The project owner, Kansai Electric Power, the academic experts from the university, and the Ministry of Construction that conducted the inspection. They all made truly irresponsible statements. The newspaper company is equally guilty. They reported their statements at face value.
The government's final inspection was also sloppy. They simply checked documents and did not actually inspect anything. Of course, they did not inspect for things like poor welding.
The ones who are always to be pitied are the private contractors who are commissioned for construction design or execution and are falsely accused.
In the end, the cause of the Wachi Dam accident was a design error. The result was completely opposite to the initial report of "Poor welding work or unthinkable design error."
It should have been reported correctly as: "Design error or unthinkable poor welding work."
This event clearly shows how irresponsible authoritative organizations, academic experts, and news media can be.
Asahi Shimbun Morning Edition (July 3, 1967)
Poor welding work or unthinkable design error
Why did the 35-ton iron water gate blow away? Toshio Morioka, Vice President of Kansai Electric Power, stated that since there was no abnormality in the concrete supporting the water gate, he suspects "there may have been a defect in the welded parts of the water gate or in the attachment to the concrete pillars," and says they will thoroughly investigate the structure of the water gate.
Professor Ishihara, Director of the Kyoto University DPRI, shares this opinion, stating, "This type of dam is a common one that has been around for a long time. It has been thoroughly researched in terms of design, and a design error is unthinkable. It is more appropriate to consider it poor workmanship in the welding or installation of the gate."
By the way, this dam was designed with a low concrete foundation and a large water gate because the Yura River, the water source, has a narrow river width despite its large floods. In other words, the water pressure received by the water gate is extremely large. Therefore, what can be considered is that the dam was full, and more water pressure than expected was applied, causing the welded and attached parts of the gate to break. Regarding this point, the argument from the Iron Structure Design Department of Hitachi Zosen Sakurajima Works in Osaka, which built the water gate, is as follows.
We have built countless water gates of this type so far. However, we have never had an accident. As for the water gate in question, we did not subcontract it and built it responsibly at the Sakurajima Works. Even regarding the welding and attachment parts pointed out, we do not think at all that they could be the cause of the accident.
If so, what is the cause? Since there are many hydroelectric dams in our country that use rivers, this accident has raised major issues in various fields. Moreover, it is said that it passed the inspections of both the Ministry of Construction and the Ministry of International Trade and Industry. Hitachi Zosen is rushing staff to the site to investigate, and says they will prepare materials and clarify the cause within the 3rd.
There was no abnormality during the inspection
[Statement by Masamitsu Matsumura (42), Director of the Kinki Regional Construction Bureau Wakayama Construction Office, who inspected Wachi Dam]
I am surprised to hear the news. I was the director of the Fukuchiyama Construction Office until this April, and since it was a dam that started construction at that time, I went to the site on June 26 for the completion inspection. I inspected the condition of the dam, whether the gate moves, and what the backup power supply is like, but there were no abnormalities as far as that was concerned.