APPENDIX B: OBSERVATIONS OF SNOW DEFORMATION BY A WHEEL
The purpose of this study was to examine the deformation of snow around a
rolling wheel and to identify mechanisms and parameters that could lead to an
improved motion resistance model for shallow snow.
Deformation experiments were conducted in areas of undisturbed snow that
were marked by chalk dust. Holes in the snow, which were punched both perpen-
dicular to and in the direction of vehicle travel, were coated with carpenter's chalk
dust. This was done by giving a plastic bottle of chalk dust with a tapered nozzle a
quick squeeze into the hole. A 12.5-mm (1/2-in.) diameter dowel was used to punch
the holes, which were placed 76.2 mm (3 in.) apart (Fig. B1). After emplacing the
dust, a vehicle was driven into the marked area such that the axle passed through
the row of perpendicular holes, then the vehicle was backed out. Whenever possible,
the wheel was undriven. The snow was then carefully removed to reveal a cross
section of the deformed area and the lines formed by the chalk (Fig. B2). Density
measurements were made using a 100-cm3 sampler, which had a 6- by 3-cm cross
section. Air and snow temperatures were recorded and, in some cases, so was the
Three different vehicles were used, although most of the experiments used the
CRREL instrumented vehicle. Tire data for each vehicle are in Table B1.
Results and observations
Photographs and documentary data are presented in Figures B3B5. From these
figures it can be seen that, as the wheel rolls forward in the snow pack, deformation
occurs in all three directions. In the following discussion, forward is the direction in
which the vehicle is moving, perpendicular refers to the direction perpendicular to
Figure B1. Snow marked with chalk-dust-filled holes.