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The Delft Sand, Clay & Rock Cutting Model, 2019a

The Delft Sand, Clay & Rock Cutting Model, 2019a

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<strong>Rock</strong> <strong>Cutting</strong>: Atmospheric Conditions.<br />

Figure 8-36: <strong>The</strong> Mohr circle for UCS and cohesion.<br />

Now shear failure will occur if the minimum principal stress σmin is larger than the tensile strength σT, thus:<br />

(8-124)<br />

min<br />

T<br />

If equation (8-124) is true, shear failure will occur. Keep in mind however, that the tensile strength σT is a negative<br />

number. Of course if the minimum normal stress min<br />

or in the graph, Figure 8-38, T /c is positive, tensile<br />

failure can never occur. Equation (8-124) can be transformed to:<br />

cos<br />

<br />

<br />

<br />

<br />

<br />

<br />

T<br />

<br />

c<br />

sin<br />

<br />

<br />

1<br />

tan<br />

<br />

cos <br />

<br />

<br />

cos tan tan sin<br />

(8-125)<br />

Substituting equation (8-108) for the shear angle β gives:<br />

<br />

sin<br />

<br />

<br />

T 2<br />

<br />

<br />

<br />

cos tan tan sin<br />

<br />

c <br />

cos<br />

2<br />

<br />

<br />

<br />

<br />

(8-126)<br />

1<br />

tan<br />

<br />

cos <br />

This can be transformed to:<br />

<br />

<br />

<br />

sin<br />

<br />

<br />

T<br />

2<br />

1<br />

sin<br />

<br />

<br />

1<br />

c cos<br />

<br />

cos<br />

<br />

<br />

2<br />

<br />

<br />

(8-127)<br />

Copyright © Dr.ir. S.A. Miedema TOC Page 281 of 454

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