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Ice lenses in natural soil are normally formed in a thermal gradient regime, and this permits the development of an undulating frost line if a range of pore sizes exists. Evidence is presented that suggests that the undulating nature of the ice-water interface permits the ice lens to form over the smaller pores of the system. Although fractions with only a limited particle size range have been studied, the results support the use of particle size as a valid basis for assessing frost susceptibility.

Heave and moisture intake and explusion were measured in four soil samples at different overburden pressures from 0.5 to 4 kg/cm². A step change in temperature, a requirement of the procedure, was imposed at one end of the sample, which was originally at a uniform temperature, to induce unidirectional freezing in a specially-designed test cell. Soils were medium in texture and had obtained along the proposed Mackenzie HIghway, N.W.T. The response to pressure and freezing conditions imposed were similar for all soils. Of particular note was the constancy in the heave rate throughout each test. At high pressures, water was expelled from the sample initially, but in all cases this was followed by water intake after the rate of frost penetration had decreased.

One of the typical features of the frost heaving phenomenon described i the authors' paper is that the total heave rate is essentially constant for any particular overburden pressure and cold side temperature. The fact that a large change in rate of frost penetration occurs after the step change in temperature in the cold side has been imposed indicates that the rate of frost penetration does not have a significant effect on the total heave rate.

The results of a 3-year insulated road study showed that frost penetration inward from the edge of an insulated area is about the same as the downward penetration on a control section. Moisture accumulated in the frost-susceptible subgrade after the frost line penetrated the insulation. During periods of rapid cooling, the temperature of the surface above an insulated pavement may be lowered sufficiently to permit surface icing if atmospheric moisture conditions are suitable. Terminating the insulation without feathering induces abrupt changes in elevation in the roadway as a result of heaving.

Concerning the influence of overburden pressure on the relation between rate of heave and cold-side temperature, studies show that the heave rate for various overburden pressures tends to converge as the cold-side temperature is lowered, and the maximum rates of ice accumulation at low pressures occur at temperatures closer to 0°C than do those at high pressures. Evidence is also presented that a heaving zone is involved in frost action rather than a freezing plane. This zone extends over an increasingly greater temperature range and distance as the overburden pressure is increased. Using the concept of a heaving zone leads to a method for calculating the heave-decrease curve. The period of heave decrease is marked by a rapidly increasing ice segregation ratio and a reduced frostpenetration rate.

A soil frost susceptibility test is proposed. The method involves the unidirectional freezing of a saturated sample by imposing a step freezing temperature at one end of the specimen and measuring the heave rate. The two most important conditions that influence heave rate during the test are the overburden pressure and the freezing temperature. Results show that the heave rate can be expressed as an exponential function of the applied overburden/freezing temperature ratio. The desirable features of the proposed freezing technique and the method of interpreting the results are outlined., 3rd International Conference on Permafrost, July 10-13, 1978, Edmonton, Alberta, Canada

This study was concerned with determining the effect of rate of freezing on frost action under laboratory conditions. This was done for the saturated and near-saturated moisture conditions of the soil. The rate of freezing was measured both in terms of heat flow and rate of frost penetration. Three soils of widely differing properties were used to bring out major differences in behavior to freezing. The results show a positive relation between net heat flow or frost penetration rate and heaving rate. Increasing the rate of heat flow away from the freezing plane in all cases increased the rate of moisture flow to the freezing plane and consequently also the heaving rate. This was shown to be true for the three soils studied at high moisture contents. It is not correct to compare the frost susceptibility of different soils in laboratory freezing experiments on the basis of equal rates of frost penetration when, in fact, this does not occur in the field. The rate of heat extraction used in laboratory tests of frost heaving should be related to the actual heat flow in the environment of the soil. The results presented should be useful in setting up practical laboratory freezing procedures for the realistic evaluation of the frost susceptibility of soils in the field.

This Digest contains a brief description of the physical processes involved in ground freezing and frost heaving and some suggestions on ways to prevent or diminish frost damage to various structures.

The effect of frost on a prestressed tie-back system of excavation bracing is described. Measurements of the horizontal movement of the wall as well as the changes in the prestressing force in the tendons, were made during the winter of 1965-66. These indicated that although considerable frost pressures did exist, the tendon loads were lower than had been anticipated owing to plastic flow creep in the bracing system. Suggestions for future installations were made.

On trouvera dans le présent Digeste une brève description des processus physiques impliqués dans la congélation du sol et dans le soulèvement par le gel ainsi que des suggestions concernant les moyens à employer pour empêcher ou diminuer les dommages causés aux ouvrages par le gel.

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.