Wind tunnel measurements of adobe abrasion by blown sand: profile characteristics in relation to wind velocity and sand flux

Abstract

Blown sand causes various damages, such as extensive abrasion to crops, structural wear of facilities and buildings, and abrasion of soil clods and clayey materials generating fine particulate matter. In this study, experiments conducted in a straight-line blowing wind tunnel confirmed field observations and provided useful information for understanding abrasion profiles created by sand drift. Abrasion rates of 20 adobe blocks in a pile 50 cm high were determined at wind velocities of 10, 12, 14, 16, 18, 20 and 22 m s −1. Wind velocities at eight different heights were measured with a wind profiler, and the transport rate of sand flux was determined by a step-like sand trap. The rate of abrasion and sand transport increased exponentially with increasing wind velocities. Abrasion profiles obtained in the wind tunnel showed good consistency with previous observations in the field. The height of maximum abrasion shifted upward from 5 to 12·5 cm as wind velocity increased. Also, as wind velocity increased, the relative amount of saltating sand decreased under the height of 5·0 cm, but increased above 7·5 cm. Comparison of the rate of abrasion with the mass transport rate yielded a strong linear relationship ( r 2=0·99). The abrasion capacity of the saltating sand (defined as the ratio of abrasion rate to aeolian sand transport rate) increased logarithmically with wind velocity, and its peak value occurred at a height of 20–22·5 cm. The experiment demonstrated that adobe abrasion by aeolian sand was affected by both abrasion capacity and the sand transport rate. Shifting of height of maximum abrasion with wind velocity was mainly due to a corresponding mass change in the structure of the aeolian sand flow.