Evert Hoek

Practical estimates of rock mass strength

The Hoek-Brown failure criterion was originally developed for estimating the strengths of hard rock masses. Because of the lack of suitable alternatives, the criterion has been applied to a variety of rock masses including very poor quality rocks, which could almost be classed as engineering soils. These applications have necessitated changes to the original criterion. One of the principal problems has been the determination of equivalent cohesive strengths and friction angles to meet the demands of software written in terms of the Mohr-Coulomb failure criterion. This paper summarises the interpretation of the Hoek-Brown failure criterion which has been found to work best in dealing with practical engineering problems.

Reliability of Hoek-Brown estimates of rock mass properties and their impact on design

This technical note examines the reliability of a slope stability calculation and a tunnel support design calculation.

Putting numbers to geology—an engineer's viewpoint

Abstract Assigning numbers to geology requires a delicate balance between the commonly held opinion that geology cannot be quantified and the over-optimistic view that every physical quantity can be described in precise mathematical terms. In reality, many geological characteristics cannot be quantified precisely and intelligent guesses based upon experience and logical arguments are the best that can be hoped for. This paper explores the processes used to make some of these guesses and describes how the results are then applied to engineering design. It is shown that, with care, rational engineering decisions can be made in spite of the limitations of the input data. In recent years the development of computer hardware and software has made it much easier to investigate the influence of ranges of values for each of the input parameters. However, care has to be taken that the design is driven by sound geological reasoning and rigorous engineering logic rather than by the very attractive images that appear on the computer screen.

Design of Large Powerhouse Caverns in Weak Rock

Publisher Summary This chapter presents design of large powerhouse caverns in weak rock. Weak rock is rock that fails when subjected to the stress levels induced by the excavation of large underground caverns at depths of 100–300 m below surface. Sedimentary rocks such as bedded sandstones, shales, siltstones, and mudstones are among the rocks that fall into this category. Tunnels and caverns associated with underground hydroelectric projects are sometimes excavated in rock masses of this type. Estimating the strength and deformation characteristics of weak rock masses is an uncertain process, and large variations in properties can be anticipated, particularly in bedded sedimentary rocks. Precise analysis of the stresses and deformations, induced by the excavation of the caverns, is not possible and the designer has to rely on parametric studies, in which the in situ stresses and material properties are varied over their maximum credible range to establish general behavioral trends.