| Case Name |
The closing support timber which was installed in order to build the bridge pier collapsed. |
| Pictograph |
|
| Date |
September 7, 1991 |
| Place |
Soka City, Saitama Prefecture |
| Location |
The field of Saikachido Bridge reconstruction |
| Overview |
The gravel inside the space closed by the sheet pile was drilled by a clamshell. During the work, the closing support timber collapsed with the big sound, and two workers were crushed to death and other two workers got injured. |
| Incident |
The gravel inside the space which was closed by the sheet pile for building the bridge pier was drilled by a clamshell which was set on the ground. During the work, the closing support timber collapsed with the big sound. Two workers were crushed to death and other two workers got injured. Though the idea drawing showed that three steps of the support timber were to be installed in total inside the closing as the excavation made advance, the gravel was dug to the bottom without the support timber of the third step, which was the reason for the accident. |
| Sequence |
* In the field, the first excavation was carried out at first, and the support timber of the first step was installed on 29th August.
* The secondary excavation was continuously advanced, and the support timber of the second step was installed on the 3rd September.
* Then, the third excavation was started. Usually, the last excavation is started after the support timber of the third step is installed after the third excavation, however, the excavation was advanced until the two-thirds of the floor was dug without the support timber of the third step.
* At last the support timber which had kept the incomplete form began to creat on the 7th September.
* At first, 4 bolts of the angle brace, which were set at the corner division of the upper river side of the support timber of the second step, broke at around 9:00 in the morning. The angle brace at the corner connected consisted of supporting beams which were associated in the stage difference. The bolt which broke during the work in the afternoon was repaired. As the 4 bolts of the angle brace which were set at upper land side of the support timber of the first step had broken, they were repaired.
* The 4 bolts of the angle brace which were set at upper land side of the support timber of the second step broke at around 2:50 p.m.
* After five minutes, at around 2:55 p.m., the closing support timber collapsed from the land side. |
| Cause |
* The biggest problem is that the gravel was dug to the bottom without the support timber of the third step.
* For the support timber installed at the first step and the second step, the angle brace described in the plans had hardly been installed. The builder had installed the angle brace only at 4 corner divisions of 28 places of one step. There was a problem in the corner division in which the angle brace was barely installed. Though 10 bolts were necessary for bonded surface of the angle brace which connected the length edge and the narrow side of the supporting beams, but they were connected just by 4 bolts actually. The intersection point of the supporting beams should have been fixed by corner piece and bolts, but they were actually just piled up actually.
* Moreover, it turned out that there were no reinforcement metallic material of the giraffe jack. |
| Knowledge Comment |
The construction should be carried out on the basis of the scheme of execution. |
| Background |
* In the investigation of the police, it seems that the support timber of the third step, which was regarded as a main reason of this accident, was to be installed after excavation had finished because it might lie in the way. The materials was not delivered until 7th September, though they had been arranged already. And, most of the angle braces were removed for the purpose of improving the efficiency of the excavation by clamshell as much as possible. Soka Police assume that the fact that the number of the bolts which connected the angle braces was so little is the result of believing that it was enough. Though it cannot be called a direct cause of the accident, the mistake had already been made in the field before the construction. In spite of the excavation over 10m depth, the prior notification of the scheme of execution determined by the 88th section of Industrial Safety and Health Law had not been sent to the Labor Standards Inspection Office under jurisdiction.
* While the director of Urawa Construction & Engineering who had inspected the field about one month before the accident gave an indication to the field deputy because he noticed that the notification had not been issued, it was not actually sent. |
| Sequel |
Three persons of the field deputy, the qualified engineer with a license and the field deputy of the contractor were accused of the involuntary manslaughter injury in the business, and they were indicted to the District Public Prosecutor's Office in the document. After the accident, the contractor increased the number of inspection of the field by three times and the instruction to the field which had been carried out verbally was documented in order to prevent failing to report the accidents to the Labor Standards Supervision Office, and it took action to prevent a recurrence of such an incident. |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Insufficient Analysis or Research, Insufficient Prior Research, Carelessness, Insufficient Understanding, Planning and Design, Poor Planning, Malicious Act, Rule Violation, Bodily Harm, Death, Failure, Large-Scale Damage
|
|
| Sources |
Measures for preventing a recurrence learning from 70 examples of grave accidents - construction accident - , Nikkei Construction
|
| Number of Deaths |
2 |
| Number of Injuries |
2 |
| Consequences |
In response to the accident at Saikachido Bridge, the Ministry of Construction also tackled the development of the method for cofferdam with short strut which was simple and secure. The result of the development is "angle block". The tip of the short strut and the angle brace are precasted as an integrated member. The Ministry of Construction promoted this method to the construction under the direct jurisdiction of the government, which can lessen the man-made mistake in the construction of the short strut. |
| Field |
Civil Engineering
|
| Author |
TANAKA, Nobuyuki (Japan Engineering Consultants Co., Ltd.)
|
|
