Analysis of Schmidt hammer rebound test results with repetitive impacts for determining the mechanical characteristics of weathered pyroclastic rock surfaces: a case study along the Isotake coast, Japan

Cliffs located along the Isotake coast, Shimane, Japan, are characterized by the development of indents without rockfalls and by the occurrence of rockfalls without indents—even though these cliffs have the same geology. An analytical method was developed to determine the mechanical properties of the rock surfaces of a coastal cliff. Twenty continuous impact repetitions of a Schmidt hammer were applied normal to the cliff surfaces in each test. The results of the tests (26 with indents and 22 without indents) showed a gradual increase in the rebound value with increasing number of repetitions. A new exponential equation was proposed in this study to describe the features of the weathered surfaces. The changes in the results were well approximated by this equation, and the approximation clearly distinguished between the two types of weathered surfaces, with higher rebound values at the surfaces of the cliffs with indents than at the surface of cliffs without indents. The homogeneity and heterogeneity of the surface and inner body of the cliff rock can also be modelled by the coefficients in this equation.