Experiments were performed in a shear cell device with adjustable lower wall velocity. Glass spheres with a mean diameter of 3 mm were used as granular materials. Image processing technology and a particle tracking method were employed to measure the average and fluctuation velocities in the streamwise and the transverse directions. Because of gravitation force, the flows consist of both a solid-like region with higher and more uniform velocities in the lower test section and a fluid-like region in the upper part. The velocity fluctuations were anisotropic and were greater in the streamwise direction. By tracking the movements of particles continually, the variation in the mean-square diffusive displacements with time was plotted and the self-diffusion coefficient was determined. The self-diffusion coefficients in the streamwise direction were much higher than those in the transverse direction. The dependence of the diffusion coefficients on the velocity fluctuations and the shear rate were discussed.

We performed laboratory experiments of dry granular chute flows impinging an obstructing wall. The chute consists of a 10 cm wide rectangular channel, inclined by 50°relative to the horizontal, which, 2 m downslope abruptly changes into a horizontal channel of the same width. 15 l of quartz chips are released through a gate with the same width as the chute and a gap of 6 cm height, respectively. Experiments are conducted for two positions of the obstructing wall, ͑i͒ 2 m below the exit gate and perpendicular to the inclined chute, and ͑ii͒ 0.63 m into the horizontal runout and then vertically oriented. Granular material is continuously released by opening the shutter of the silo. The material then moves rapidly down the chute and impinges on the obstructing wall. This leads to a sudden change in the flow regime from a fast moving supercritical thin layer to a stagnant thick heap with variable thickness and a surface dictated by the angle of repose typical for the material. We conducted particle image velocimetry ͑PIV͒ experiments by recording the moving material from the side with charge coupled devices ͑CCD͒ cameras. The experiment was also video recorded. From the CCD data velocities were also deduced using the PIV technique. In order to compare the results here we describe the experiments for the same material and the same gap width of the silo gate but for the two positions of the obstructing wall. Analysis of the shock front formation and propagation upslope, evolution of the height of the supercritical flow, impact velocity and momentum are presented and discussed in detail. Computed and derived shock front heights match well.

The present study on granular material flows develops analytical relations for the flow-induced particle diffusivity and thermal conductivity based on the kinetic theory of dense gases. The kinetic theory model assumes that the particles are smooth, identical, and nearly elastic spheres, and that the binary collisions between the particles are isotropically distributed throughout the flow. The particle diffusivity and effective thermal conductivity are found to increase with the square root of the granular temperature, a term that quantifies the kinetic energy of the flow. The theoretical particle diffusivity is used to predict diffusion in a granular-flow mixing layer, and to compare qualitatively with recent experimental measurements. The analytical expression for the effective thermal conductivity is used to define an apparent Prandtl number for a simple-shear flow; this result is also qualitatively compared with experimental measurements. The differences between the predictions and the measurements suggest limitations in applying kinetic theory concepts to actual granular material flows, and the need for more detailed experimental measurements.

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Velocity and depth are crucial field variables to describe the dynamics of avalanches of sand or soil or snow and to draw conclusions about their flow behavior. In this paper we present new results about velocity measurements in granular laboratory avalanches and their comparison with theoretical predictions. Particle image velocimetry measurement technique is introduced and used to measure the dynamics of the velocity distribution of free surface and unsteady flows of avalanches of non-transparent quartz particles down a curved chute merging into a horizontal plane from initiation to the runout zone. Velocity distributions at the free surface are determined and in one case also at the bottom from below. Also measured is the settlement of the avalanche in the deposit. For the theoretical prediction we consider the model equations proposed by Pudasaini and Hutter ͓J. Fluid Mech. 495, 193 ͑2003͔͒. A nonoscillatory central differencing total variation diminishing scheme is implemented to integrate these model equations. It is demonstrated that the theory, numerics, and experimental observations are in excellent agreement. These results can be applied to estimate impact pressures exerted by avalanches on defence structures and infrastructures along the channel and in runout zones.