The frost heaving forces developed under a 1 ft (30.5 cm) diameter steel plate were measured in the field throughout one winter. The steel plate was fixed at the ground surface with a rock-anchored reaction frame. Heave gauges and thermocouples were installed at various depths to determine the position and temperature of the active heaving zone.The general trend was for the surface force to increase as the winter progressed. When the frostline approached maximum depth the force was in excess of 30 000 lb (13 608 kg). Estimates of the heaving pressure at the frostline ranged from 7 to 12 psi (0.49 to 0.84 kg/cm2) during this period.The variation of surface heaving force was closely associated with weather conditions. Warming trends resulting in a temperature increase of the frozen layer caused the forces to decline.