Solifluction processes on permafrost and non‐permafrost slopes: results of a large‐scale laboratory simulation

We present results of full‐scale physical modelling of solifluction in two thermally defined environments: (a) seasonal frost penetration but no permafrost, and (b) a seasonally thawed active layer above cold permafrost. Modelling was undertaken at the Laboratoire M2C, Université de Caen‐Basse Normandie, Centre National de la Recherche Scientifique, France. Two geometrically similar slope models were constructed using natural frost‐susceptible test soil. In Model 1 water was supplied via a basal sand layer during freezing. In Model 2 the basal sand layer contained refrigerated copper tubing that maintained a permafrost table. Soil freezing was from the top down in Model 1 (one‐sided freezing) but from the top down and bottom up (two‐sided freezing) in Model 2. Thawing occurred from the top down as a result of positive air temperatures. Ice segregation in Model 1 decreased with depth, but in Model 2, simulated rainfall led to summer frost heave associated with ice segregation at the permafrost table, and subsequent two‐sided freezing increased basal ice contents further. Thaw consolidation in Model 1 decreased with depth, but in Model 2 was greatest in the ice‐rich basal layer. Soil shear strain occurred during thaw consolidation and was accompanied by raised pore water pressures. Displacement profiles showed decreasing movement rates with depth in Model 1 (one‐sided freezing) but ‘plug‐like’ displacements of the active layer over a shearing basal zone in Model 2 (two‐sided active layer freezing). Volumetric transport rates were approximately 2.8 times higher for a given rate of surface movement in the permafrost model compared with the non‐permafrost model. Copyright © 2008 John Wiley & Sons, Ltd.