Block Size Distribution and Quality Classification in Naturally Fractured Rocks

Abstract

A refined rock mass classification is proposed which exposes percentages of different quantities as solid, massive, blocky, fractured, and crushed. It is shown that some of the classical rock quality designation indices with a single value of classification fail to provide detailed information. In fact, different rock mass compositions might lead to the same single values, but they may be entirely different in the overall rock mass behavior. The basis of the methodology presented in this paper is the cumulative frequency distribution of intact lengths which is drawn on a specially developed semi-logarithmic paper so as to identify different quality regions. Additionally, an empirical relationship is proposed which relates the classical Rock Quality Designation (RQD) value to descriptive values of these graphs. Besides the quality, percentages obtained in this manner might give some clues about the tectonic activities especially in the igneous rock environments. Application of the methodology has been presented for two regions in the Kingdom of Saudi Arabia.