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Case No.102

The sides of an excavation trench collapse during work to remove earth that had fallen into the trench at the construction site of an agricultural drainage channel

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[Description of the Accident]

This accident took place during work to remove earth that fell into an excavated trench due to a burst in a water pipe at the construction site for agricultural drainage channel. On the day of the accident, it was planned to excavate a trench for two drainage pipes (some eight meters long) along the road by using a vehicle-type excavation machine to install the drainage pipes. However, when a water pipe that was already buried in the trench at a depth of 70 centimeters below the ground level was cut by a landslide, some earth fell into the trench and it became necessary to remove it. Because of this, three workers were engaged in carrying out work to remove the earth from the excavated trench. At around five minutes after the start of the work, a worker who was working on the surface noticed a crack in the earth near the excavation and gave a warning to the three workers who were working in the trench. Although all of the three sensed danger and tried to escape, it was too late, and the slope collapsed leaving only the asphalt paving of the road. Because of this, the entire body of the victim who was carrying out work to remove the earth at the bottom of the trench was buried by the fallen earth, leaving only the top of his helmet still showing.

[Causes supposed]

1. Firm measures to protect against the collapse of the natural ground were not taken.

2. Work was being carried out without a clear determination, direct instructions, etc., of the work methods by the operations chief of excavating natural ground and timbering of the earth.

3. Appropriate operations plans were not formulated.

4. Although there were no direct instructions from the site representative, the operations chief, etc., the work was carried out at workers' own discretion.

5. The slope of the walls of the excavated trench made it easy for them to collapse.

[Type of business] Water and sewage construction
[Caused by] Natural ground
[Type of accident] Collapse
[Number of victims] One fatality