(EE) was scaling a rock brow with the scoop bucket outby the #2 working section on the 2A belt between Breaks #12 and #13. While scaling the rib, the EE inadvertently dislodged three timbers. While installing the timbers the rib rolled out, measuring approximately 17 feet by 24 inches by 12 inches, and struck the EE in the lower thigh, causing a laceration resulting in six sutures