PARTICLE SIZE AS A BASIS FOR PREDICTING FROST ACTION IN SOILS

抄録

Maximum heaving pressures caused by ice lens growth were determined experimentally for saturated specimens consisting of fragmental particles in several size ranges. Theoretical predictions show that the pores produced by the smaller particles in the system are responsible for the maximum heaving pressures measured. The suggestion is that the ice-water interface assumes an undulating configuration over the smaller pores when ice proliferation stops, and hence heaving pressures rise to a maximum.Particle size seems to be an adequate basis for predicting frost susceptibility in practice although the exact amounts and size limits permissible have not been evaluated.The nature of the failure caused by frost action is not the same for all engineering structures. Failures by "rate of heave" and "heaving pressure" should both be considered if the possibility of frost damage exists. The results substantiate earlier conclusions that there is no sharp dividing line between frost-heaving and nonfrost-heaving soils.Recent studies by the author have shown that the theory of Everett (2) and Everett and Haynes (3) provides a realistic basis for the growth of ice lenses from pure water in porous systems of simple and uniform geometry. Difficulties arise when the theory is applied to soils which have a more complex porous structure because a grain size, and hence a pore size, distribution exists. For a porous system of this complexity, the theory as it stands is not adequate for prediction, since little is known about the size of pores, in a given pore size range, that determine the heaving pressure characteristics.The two laboratory approaches for assessing frost susceptibility ("rate of heave" and "heaving pressure") are not entirely compatible, but it is clear and consistent that soils which are not frost-susceptible should not exhibit any measurable heaving pressure or rate of heave. Soils that have a low heaving pressure may show a considerable rate of heave under little or no restraint. On the other hand, some soils that exhibit a high heaving pressure from ice lens growth, such as dense clays, may due to permeability limitations have a sufficiently low heaving rate to be acceptable for some engineering structures subject to freezing conditions, (Fig. 1).[graph]The trend in soil engineering has been to predict the frost susceptibility of a soil from its particle size characteristics through relationships determined by "rate of heaving" experiments. Many organizations have carried out such tests but there are no generally-accepted limits to particle size or percentage of fines which determine frost susceptibility.In this paper attempt is made to elucidate further the mechamism of heaving, particularly the development of "heaving pressures" by ice lens formation in relation to the particle size distribution of the sample. It will be shown that from measurements of heaving pressure it is possible to obtain an estimate of the sizesof particles which are responsible.