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Rock Mechanics.pdf - Mining and Blasting

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Figure A.9 Bolt load–extension<br />

curve obtained in a pull-out test<br />

on a 25 mm diameter, 1.83 m long<br />

rock-bolt anchored by a four-leaf<br />

expansion shell (after Franklin <strong>and</strong><br />

Woodfield, 1971).<br />

APPENDIX C ROCK–SUPPORT INTERACTION ANALYSIS<br />

C.3.3 Support stiffness <strong>and</strong> maximum support pressure for ungrouted<br />

mechanically or chemically anchored rockbolts or cables<br />

Input data<br />

Important items of data required in this case are obtained from the results of pull-out<br />

tests. A typical load-extension curve is shown in Figure A.9. The variables used to<br />

determine the constant, Q, are defined on this figure.<br />

l = free bolt or cable length;<br />

db = bolt diameter or equivalent cable diameter;<br />

Eb = Young’s modulus of bolt or cable;<br />

Tbf = ultimate failure load in pull-out test;<br />

ri = internal tunnel radius;<br />

sc = circumferential bolt spacing;<br />

sℓ = longitudinal bolt spacing;<br />

Q = load-deformation constant for anchor <strong>and</strong> head, given<br />

(from Figure A.9) by<br />

Q = (u2 − ueb2) − (u1 − ueb1)<br />

T2 − T1<br />

where u1, T1 <strong>and</strong> u2, T2 are two points on the linear portion of the load-extension plot.<br />

578

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