An employee was operating a boom in a bucket truck. One outrigger of the truck was placed on the pavement and the other outrigger of the truck was on soft ground. The outrigger that was on soft ground sunk into the ground and caused the truck to roll and the weight to shift on the truck. The employee and bucket then fell to the ground. The employee suffered L1 and L2 vertebrae fractures and a right cheek laceration. Fall protection was worn at the time of the incident.