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JICOSH Home > Case Studies > Case No.84
Case No.84

Wheel crane toppled when outriggers sank into soft ground during lifting operations

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[Description of the Accident]

During formwork lifting work, a wheel crane suddenly toppled over when the extended outriggers sank into the soft ground.

On the day of the accident, work to install concrete formwork by a wheel crane was scheduled to be carried out at the construction site for a school. The operator installed the crane at the working site, expanded the outriggers to the maximum, and laid wooden blocks in a double cross under the outriggers.

After finishing these preparations, he expanded the auxiliary jib to the maximum, slung the framework with the weight of about 600 kg some 32 meters from the crane, and started his lift. When the lift was about 50 cm off the ground, the crane suddenly started leaning.

While the operator quickly tried to rearrange his load, he was too late and the wheel crane toppled over before anything could be done.

[Causes supposed]

1. While the operator expanded the outriggers to the maximum prior to the actual lifting work and laid wooden blocks under them in a double cross to prevent any sinking, the blocks were too small and did not provide enough support for the soft ground.

2. The operator failed to make detailed arrangements with the general contractor of the construction, etc., about the work scheduled for that day. Accordingly, the work plan was not sufficient.

[Type of business] Overland goods handling
[Caused by] Wheel crane
[Type of accident] Fall
[Number of victims] None