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Rock Mechanics.pdf - Mining and Blasting

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Figure 3.22 The great circle <strong>and</strong> its<br />

poles which define the orientation of<br />

a plane.<br />

THE HEMISPHERICAL PROJECTION<br />

of observations made for each orientation interval are plotted as radii. Dips <strong>and</strong> dip<br />

directions may be added at the periphery of the circular diagram. This method of<br />

presenting discontinuity orientation data is much less useful <strong>and</strong> versatile than the<br />

hemispherical or stereographic projection which will be discussed in the following<br />

section.<br />

3.6 The hemispherical projection<br />

3.6.1 Hemispherical projection of a plane<br />

The hemispherical projection is a method of representing <strong>and</strong> analysing the threedimensional<br />

relations between planes <strong>and</strong> lines on a two-dimensional diagram. The<br />

method was first developed as a tool for use in structural geology but has been extended<br />

<strong>and</strong> used to solve engineering problems. The basis of the method <strong>and</strong> its classic<br />

geological applications are described by Phillips (1971). <strong>Rock</strong> engineering applications<br />

are described in detail by Goodman (1976, 1989), Hoek <strong>and</strong> Brown (1980),<br />

Hoek <strong>and</strong> Bray (1981) <strong>and</strong> Priest (1985, 1993). Application of the technique to the<br />

problem of structurally controlled failures around underground mining excavations<br />

will be discussed in Chapter 9.<br />

Imagine a sphere which is free to move in space so that it can be centred on an<br />

inclined plane as illustrated in Figure 3.22. The intersection of the plane <strong>and</strong> the<br />

surface of the sphere is a great circle, shown at the perimeter of the shaded area in<br />

71

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