The author carried out full-scale field tests and measured stresses in situ generating by bulldozers. These data were analyzed experimentally as well as theoretical by making numerical models. Five bulldozers are used on different types of soil such as cohesive soil, sandy soil and rockfill materials. Most measured stresses are much larger than the stresses calculated from nominal contact pressure. The stress variation by travelling a bulldozer on the ground, that is the time-stress tau-delta relation or curve on the oscillograph shows particular shapes as if it were random vibration.