As the pilot was taxiing to takeoff on runway 10, he encountered a truck parked on the taxiway. He then made a 180-degree left turn, taxied back down the taxiway, then made a second 180-degree left turn in an attempt to reverse direction to go around the truck. However, during the turn the airplane went off the right side of the taxiway and into some soft dirt, which required the pilot to increase power in order to get out of the dirt and back upon the runway. The pilot stated that he thought he had added too much power, and as a result, when the airplane regained the taxiway surface it proceeded across the taxiway and impacted the truck with its right wing, which resulted in substantial damage to the wing. The pilot reported no preaccident anomalies with the airplane or engine that would have precluded normal operation.