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Rock Mechanics.pdf - Mining and Blasting

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METHODS OF IN SITU STRESS DETERMINATION<br />

(a) by dip, , <strong>and</strong> dip direction, , relative to a set of global axes x, y, z. Relative<br />

to these axes, the ambient field stress components (prior to drilling the hole) are<br />

pxx, pyy, Pzz, pxy, pyz, pzx. A convenient set of local axes, l, m, n, for the borehole<br />

is also shown in Figure 5.5a, with the n axis directed parallel to the hole axis, <strong>and</strong><br />

the m axis lying in the horizontal (x, y) plane. The field stress components expressed<br />

relative to the hole local axes, i.e. pll, pln, etc., are readily related to the global<br />

components pxx, pxz, etc., through the stress transformation equation <strong>and</strong> a rotation<br />

matrix defined by<br />

⎡<br />

xl<br />

[R] = ⎣ yl<br />

xm<br />

ym<br />

⎤ ⎡<br />

xn − sin cos <br />

yn ⎦ = ⎣ − sin sin <br />

sin <br />

− cos <br />

⎤<br />

cos cos <br />

cos sin ⎦<br />

cos 0 sin <br />

zl zm zn<br />

In Figure 5.5b, the location of a point on the wall of the borehole is defined by<br />

the angle measured clockwise in the l, m plane. Boundary stresses at the point<br />

Figure 5.4 (a) A triaxial strain<br />

cell (of CSIRO design), <strong>and</strong> (b),<br />

(c), (d) its method of application.<br />

(c) (d)<br />

149<br />

(b)

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