Abstract: On July 26, 2001, Employees #1 and #2 were excavating an 18-in. deep trench for a new sewer line next to the footing of a new retaining wall. A retaining wall was located between one side of a wooden shed and a hillside. The shed was demolished days earlier. The height from the shed's foundation to the top of the sloped earth level ranged from approximately 5.5 ft to the North and approximately 7 ft to the east. As one of the employees was breaking up the earth within the trench with a jackhammer, the retaining wall collapsed upon both of them. Emergency medical services were summoned and both employees were transported to the hospital. Both employees were hospitalized to receive medical treatment. Employee #2 sustained a fracture to his pelvic girdle in the accident, but was treated and released. As for Employee #1, he suffered serious injuries consisting of a fractured femur and acetabulum (a cup-shape socket in the hipbone). The employees were not licensed to perform the excavation work. The factors contributing to the accident were that the retaining wall was not shored and the employees were undermining the foundation of the retaining wall.