  An experimental apparatus measuring free-surface deformation of a centrifuged
granular pile is developed. By horizontally rotating a quasi two-dimensional
granular pile whose apex is located at the vertical rotation axis, the
resultant force of gravity and centrifuge yields the deformation of the
granular pile. In this setup, centrifugal force depends on distance from the
rotation axis whilst gravitational force is constant everywhere. Therefore,
free-surface deformation by various centrifuge degrees can be systematically
examined using this apparatus. In the system, a small unit consisting of a
camera and computer is rotated with the granular sample to record the
rotation-induced deformation. To evaluate the validity of the system,
deformation of a rotated water surface is first measured and analyzed. The
obtained data are properly explained by the theoretical parabolas without any
fitting parameter. Next, we measure the deformation of non-cohesive and
cohesive granular piles using the developed apparatus. Both granular samples
show the significant deformation of granular pile and finally develop steep
granular slopes on the side walls. However, details of the deformation
processes depend on the cohesion strength. To quantitatively characterize the
difference, the effective strength by cohesion and granular local-slope
variations are analyzed based on the experimental results.
