Scaled physical modelling of mass movement processes on thawing slopes

This paper presents initial results from scaled geotechnical centrifuge modelling of cryogenic slope processes. Four experiments are described in which 1/10 scale planar slope models were constructed from a silty soil at gradients of 12 degrees, 18 degrees and 24 degrees. Models were frozen on the laboratory floor, and thawed in the centrifuge at 10 gravities. Frost heave, thaw settlement, soil temperature and pore water pressures were recorded. In each experiment, ten columns of 5 mm long plastic cylinders inserted through the soil profile allowed surface soil displacements to be determined, and indicated displacement profiles with depth at the end of each experiment. The 12 degrees model was subjected to four cycles of freezing and thawing, simulating four annual active-layer freeze-thaw cycles. During each thaw phase, gelifluction occurred, and average model-scale surface displacements were 18.7 mm/cycle (equivalent to 187 mm/cycle at prototype scale). In the 18 degrees model, gelifluction rates were higher, with average surface displacements of 65.1 mm/cycle at model scale, 651 mm/cycle at prototype scale. Two replicate 24 degrees frozen slope models were tested in the centrifuge, and thawing was associated with failure by mudflow. Maximum pore water pressures during thaw were similar in all models. Slope stability analysis using an infinite planar model indicated that the factor of safety against failure remained >1 in the 12 degrees model, was close to or slightly less than 1 in the 18 degrees model, and was <1 in the 24 degrees models. Copyright (C) 2001 John Wiley & Sons, Ltd.