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

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

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Exercises.<br />

16.8.5. Calc.: <strong>Cutting</strong> Forces & Mechanisms.<br />

Consider a rock with a compressive strength of 60 MPa and a tensile strength of -3 MPa. <strong>The</strong> angle of<br />

internal friction is 20 degrees, the angle of external friction is 13.33 degrees. A blade angle of 60 degrees is<br />

used and a blade height of 0.1 m and blade width w=1 m. <strong>The</strong> layer thickness is 0.1 m.<br />

<strong>The</strong> shear angle is:<br />

<br />

= 43.33 degrees<br />

2 2<br />

<strong>The</strong> cohesion or shear strength is:<br />

<br />

<br />

UCS 1<br />

sin <br />

c =21 MPa<br />

2 <br />

cos <br />

<br />

<strong>The</strong> normal stress on the shear plane is:<br />

ccos( ) N1<br />

cos( ) 12.9 M Pa<br />

sin( )<br />

<strong>The</strong> shear stress on the shear plane is:<br />

S1<br />

N1<br />

<br />

c tan =25.7 MPa<br />

<strong>The</strong> normal stress in the center of the Mohr circle is:<br />

C N1 S1<br />

<br />

tan 22.27 MPa<br />

<strong>The</strong> radius of this Mohr circle is now:<br />

S1<br />

R <br />

cos <br />

<br />

<br />

27.35 MPa<br />

<strong>The</strong> minimum principle stress of this Mohr circle is:<br />

R 5.09 MPa<br />

min C<br />

Since -5.09 MPa

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