32 - Empirical Design and Rock Mass Characterization

Abstract

This chapter discusses empirical design and rock mass characterization. Design is a decision-making process, and empirical design is defined as quantified judgment based on experience. Empirical design is the most prevalent form of design. Judgment and experience are major ingredients in rock engineering design and are the sole ingredients in the absence of other more formal methods. Empirical methods allow the engineer to proceed directly from a rock classification, based on index tests to the design of rock excavations and support systems. Empirical methods are common particularly in tunneling but also in the prediction of drilling and boring rates, assessment of rock aggregate and building stone quality, and evaluation of the susceptibility of rock excavations to weathering and erosion. The method is a powerful one with a broad range of applications. A strength criterion is an equation used to check whether rupture of rock can occur under the combination of the three principal stresses predicted at a particular location. Each type of rock has its own strength surface which, if a suitable form of equation is found, can be represented algebraically as a strength criterion.