株式会社葵組

1. Contract Situation: The construction contractor was subcontracted by Hirose Corporation as a primary subcontractor for office building earthwork, shoring, formwork, and support work in Osaka City. The contractor then undertook SMW method work and support pile installation. 2. Site Conditions: The site was on a slope with approximately two inclines, covered with steel plates. A large pile driver (No. 6, weight 28 tons per square meter) was positioned on these plates. The contractor requested Hirose Corporation to level the slope, but it was not leveled. On November 1, 2024, the contractor performed ground improvement using a pile driver. On November 2, 2024, around 2:00 PM, approximately 40 mm of rain fell within one hour. Ground improvement involved mixing cement, clay minerals, and water into backfill soil as instructed by Hirose Corporation; no replacement with high-quality soil was performed. 3. Incident Details: On November 5, 2024, at around 9:35 AM, the contractor, believing the ground had hardened after more than a day since the rain, proceeded to move the pile driver without checking ground strength. Immediately after moving the equipment over the ground improved on November 1, residual soil (a mixture of cement, clay minerals, and water) used for backfill, which had absorbed moisture, caused the ground to collapse due to insufficient bearing capacity (~8 t/㎡). The collapse caused the pile driver to overturn forward, blocking a city road, damaging a museum roof across the street, entangling power lines, knocking over a utility pole, and causing a power outage affecting approximately 20 households for three hours. Pedestrians were also injured. 4. As a result, the contractor failed to properly assess and confirm ground conditions before relocating heavy machinery after weather events or construction activities, neglecting necessary safety precautions. This negligence led to the overturning of the pile driver and subsequent public hazards on November 5, 2024.