Abstract: A contractor was installing an underground telephone cable and had dug a 1.3-meter-deep trench for the cable. The bottom of the trench descended to a depth of 4 meters at one end to connect to a manhole. The trench, which had nearly vertical walls, was about 2 meters wide at the manhole. Two sheets of 13-millimeter-thick plywood were placed at the trench walls with one screw jack between then. The employee then entered the excavation to dry concrete from around the manhole bottom. The north wall of the trench collapsed on the employee. The employee was hospitalized with a severely fractured leg for 7 days.