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

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Cliffs located along the Isotake coast, Shimane, Japan, are characterized by the development of indents without rockfalls or by the occurrence of rockfalls without indents even though the geology is the same. An analytical method was developed to determine the mechanical properties of the rock surfaces on these coastal cliffs. Twenty continuous impact repetitions of the 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 as the number of repetitions increased. 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 the equation, and the approximation clearly distinguished between the two types of weathered surfaces, with higher rebound values at the surface of the indents than those at the surface of cliffs without indents. The homogeneity/heterogeneity of the surface and inner body of the cliff rock can also be modelled by coefficients appearing in the equation.