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Rock Mechanics.pdf - Mining and Blasting

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Figure A.7 Shotcrete or concrete<br />

lining.<br />

Figure A.8 Blocked steel set.<br />

AVAILABLE SUPPORT LINE CALCULATIONS<br />

C.3 Available support line calculations<br />

C.3.1 Support stiffness <strong>and</strong> maximum support pressure for a concrete or<br />

shotcrete lining<br />

Input data<br />

Ec = Young’s modulus of concrete or shotcrete;<br />

c = Poisson’s ratio of concrete or shotcrete;<br />

tc = lining thickness (Figure A.7);<br />

ri = internal tunnel radius;<br />

cc = uniaxial compressive strength of concrete or shotcrete.<br />

Support stiffness<br />

kc =<br />

Maximum support pressure<br />

<br />

2<br />

Ec ri − (ri − tc) 2<br />

(1 + c)[(1 − 2c) r 2 i + (ri − tc) 2 ]<br />

psc max = cc<br />

2<br />

<br />

1 − (ri − tc) 2<br />

r 2 <br />

i<br />

C.3.2 Support stiffness <strong>and</strong> maximum support pressure for blocked steel sets<br />

Input data (Figure A.8)<br />

W = flange width of steel set <strong>and</strong> side length of square block;<br />

X = depth of section of steel set;<br />

As = cross-sectional area of steel set;<br />

Is = second moment of area of steel set;<br />

Es = Young’s modulus of steel;<br />

ys = yield strength of steel;<br />

ri = internal tunnel radius;<br />

S = steel set spacing along tunnel axis;<br />

= half angle between blocking points (radians);<br />

tB = thickness of block;<br />

EB = Young’s modulus of block material.<br />

Support stiffness<br />

1<br />

ks<br />

= Sri<br />

+<br />

Es As<br />

Sr3 i<br />

EsIs<br />

Maximum support pressure<br />

577<br />

pss max =<br />

( + sin cos )<br />

2 sin 2 <br />

<br />

− 1 + 2S tB<br />

EBW 2<br />

3AsIsys<br />

2Sri {3Is + XAs[ri − (tB + 0.5X)] (1 − cos )}

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