A Science for Everyone, Community

Why Frost Heaves

Frost heaves – back when I was teaching engineering uses of soils 40 years ago – were explained by osmosis, compression and fine-grained soil.  So think clay, or even better, glacial silt as your fine-grained soil.  For compression, remember that just ten or fifteen thousand years back there were some thick glaciers on top of our soil.  For osmosis, think of the difference between rain water, or snow melt, and the groundwater with it’s calcium salts under my field.  And glacial silts tend to have a lot of exchangeable ions.

The textbook phrase was “If a fine-grained soil, especially a clay, has been compressed, it will normally take in water upon reduction in compressive loading.  In many cases this intake of water may be attributed to osmosis.  The pore water already in the soil is assumed to move into regions of higher concentration between the particles.  More water is drawn into the soil in this process and gradually the water content of the mass as well as the soil volume are significantly increased. . . It has been observed that under certain conditions, when the ground freezes, the surface of the ground rises.  This is termed frost heaving.  Calculations show that in many cases the amount of heave is far more than can be accounted for by the expansion of water on freezing.  It is therefore assumed that additional water must be drawn into the freezing zone.” p.84, Hough, Basic Soils Engineering 1967

In areas that lack our fine-grained soils, frost heaves aren’t so obvious.  On our roads, the places that once had extreme frost heaves – I remember a particularly bad one that was in front of the Apeland ranch on 93 – were over excavated and the fine materials replaced with sand and gravel – so that osmosis could not occur.