The pilot stated that the purpose of the flight was to investigate the cause of an electrical power outage in the area. He had three power company patrolmen on board. After patrolling various power lines and spur connections, they came to a pole that the patrolman in the left front seat wanted to inspect more closely. After hovering near the pole for a short time, the patrolman asked if they could land. The pilot said he inspected the landing area, choosing a fairly level spot and touched down. As he lowered the collective, the skids sank into the soil. Stabilizing the helicopter with cyclic, he told two patrolmen on the left side to deplane. They disembarked, closing the doors. Suddenly the soil under the left rear skid tube gave way and the helicopter tipped left and to the rear, where the tail rotor struck the ground. The helicopter continued to roll left and the main rotor struck the ground. Post accident examination of the ground revealed that it was soft, recently plowed dirt moist from recent rain.