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Measurement of Waterdrop Impact Pressures on Soil Surfaces¹

ABSTRACT

Limited data on pressures induced by waterdrop impact on soil surfaces restricts our understanding the mechanism of soil detachment due to raindrop impact. Impact pressures on rigid surfaces are known but their application to soil surfaces is questionable. This study was undertaken to measure vertical pressures of waterdrop impact on soil surfaces. A 1-mm diam piezoelectric transducer was developed and measurements of impact pressures as a function of radial distance from drop center were made. Dickinson loam (coarse-loamy, mixed, mesic Typic Hapludoll) and Ida silt loam (fine-silty, mixed [calcareous] mesic Typic Udorthent) with bulk densities of 1.0 and 1.2 Mg/m³ and with matric potentials of –0.5 and –2.5 kPa were used. The waterdrop had a diameter of 5.6 mm and a fall height of 14 m. Average peak impact pressures were greatest at a distance of 1.8 to 2.3 mm from center of impact and of the order of 190 to 290 kPa. These stress levels are almost two orders of magnitude less than those for impact on a rigid surface. Much of the difference between soil and rigid cases was due to nonrigid, nonhomogeneous nature of the soil material. The remainder of the difference in stress levels was thought to be due to the effect of soil granularity or to the presence of surface and shear waves generated by impact.

¹ Contribution from the USDA-ARS National Soil Erosion Research Laboratory in cooperation with the Purdue Agric. Exp. Stn. Journal no. 11 035.

² Agricultural Engineer and Soil Scientist, USDA-ARS National Soil Erosion Research Laboratory; and Professor, School of Civil Engineering; Purdue Univ., West Lafayette, IN 47907.

Received for publication February 2, 1987.