Tuesday, November 14, 2006

Effect of a Subsurface Hydrophobic Layer on the Upward Movement of Water in Response to Surface Freezing Conditions.

Heath Gieselman, Robert Horton, and Joshua Heitman. 2543 Agronomy Hall, Iowa State University, Ames, IA 50011

Frost heave is the process in which wet soil with an available water source undergoes deformation and upward movement of the soil surface.  As temperature decreases at the soil surface, heat exits, and the soil is cooled.  At temperatures below freezing, the water in the soil undergoes a phase change from the liquid to the solid state.  Continued cooling of the soil surface continues removal of sensible heat stored in the material as well as latent heat produced by the phase change of water.  Freezing of that water and cooling at the surface has the similar effect as drying at the soil surface, and water moves upward toward the freezing front.  The continued upward movement of water and subsequent freezing causes mass accumulation in the formation of ice lenses.  It is this accumulation of ice that causes the upward heaving of the soil surface.  Thickening of the frozen layer causes a decrease in the temperature gradient between the soil surface and the freezing front and slows the penetration rate of the freezing front, resulting in a quasi-steady state condition. In this study the upward water movement from a fixed water supply in freezing soil columns with and without a subsurface hydrophobic treated soil layer is measured.  The vertical soil column set-up enables one-dimensional vertical heat flow by including a column-within-a-column design that minimizes radial heat transfer.  The purpose of the hydrophobic layer is to reduce the upward water flow rate.  This study examines the effects of a hydrophobic treated soil layer on water flow and ice lens formation under ideal frost heave conditions.