Flow resistivity and porosity testing of surface materials

Flow resistivity and porosity measurements have been performed on a variety of ground surface materials using a forced airflow apparatus and a microglass-bead-calibrated porosity instrument. It is found that the flow resistivity ranges from over 1 million cgs rayls/cm for concrete down to less than 100 for sand and gravel. The porosity ranges from 0.4 for dry soil to less than 0.01 for concrete. Based on these measurements, the normal absorption coefficient for a 200 Hz acoustic wave is less than 0.2 for all of the materials tested except gravel, the value of which is approximately 0.4. For standard asphalt utilized for surface pavement, for instance, the estimated normal absorption coefficient is found to be less than 0.01.