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To predict the motion of free-flowing bulk materials over a rigid base (screes, avalanches), the effect of explosive shock loads on underground constructions, pipelines, and wells, and the body deceleration upon impact on ground, one needs to know the dynamic friction coefficient, which differs significantly from that found under static and quasistatic conditions. It should be noted that determining the static friction coefficient has also not received too much attention. For instance, data on the static coefficient of friction of dry sandy ground on a smooth metal wall are presented only in [1][2][3].Below we describe a method for the experimental determination of the dynamic coefficient kf of the friction of sandy ground on a rigid wall, which does not require a direct measurement of the ground pressure on the wall, and we present some measurement results: values of k/for the motion of sandy ground with an initial density of 1.66 g/cm and humidity of 4-5 % in a smooth tube of D16T alloy in the range of stresses 0.1-25 MPa and mass velocities 0.9-40 m/sec. The procedure for determining sand stresses and mass velocities behind a shock wave front in experiments of this kind was set forth in [4].The experimental setup is shown in Fig. 1. Thick-walled tube sections 3 (inside diameter 26 mm, length from 8 to 30 cm) and 5 were mounted one inside the other with a small gap on a massive steel slab 7 and filled up with sand 4. The sand loading was induced by blasting of an explosive disk (1) 5 mm thick initiated at the center. A steel disk striker (2) 5 mm thick was placed between the explosive and the sand. The normal stress in the wave crr reflected from the steel slab was measured by a piezoelectric pressure gage 6 [5] embedded in the slab flush with its surface. A relatively thin sand layer in tube 5 is used to cushion the explosive effect on the steel slab via the wall of tube 3. To decrease the friction, a polyethylene spacer 0.05 mm thick was placed between the tube wall and the sand in the second set of experiments. The measurement results are presented in Fig. 2. Points 1 are the data obtained without the polyethylene spacer; 2, with the spacer; x is the distance from the disk striker to the lower end of tube 3. The normal stress pulse in the reflected wave

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