This document describes an index test for the determination of the protection efficiency of a geosynthetic on a hard surface, exposed to the impact load of a hemispherical object. The index test measures the change in thickness of a thin lead plate lying between the geosynthetic and a rigid support. It is also used as a performance test, by using the real rigid surface to protect and the real sequence of geosynthetics. The test is applicable to all geosynthetics with apertures smaller than 15 mm (maximum size).