Heterogeneous rock mass classification by means of the geological strength index: the <Emphasis Type="Italic">San Mauro</Emphasis> formation (Cilento,Italy)

This paper describes an application of the geological strength index (GSI) method to the San Mauro formation, which is characterized by sandstones alternating with argillaceous marls. The Sandstone/Pelite (S/P) ratio and structural complexity were determined. Geo-structural and geo-mechanical surveys were undertaken in situ and rock samples were tested in the laboratory. A map of the S/P ratio was produced showing the bedrock divided in four classes. Three ranges of GSI values were identified. The values of the intact UCS and of the constant m _i were appropriately reduced to reflect the variable presence of sandstone compared with the pelitic fraction. A “weighted average” of the intact strength properties of the hard and weak layers was adopted. The values for the intact materials were reduced from 20 to 60% depending on the GSI categories of the heterogeneous rock mass. In this way, seven classes of rock masses characterized by different values of GSI, reduced UCS and m _i values were identified.