Geomechanics and Ground Control · Geomechanics · 2 marks · Multiple choice
The failure criterion is σ₁=4σ₃+28 MPa. At A, (σ₃, σ₁)=(10, 90) MPa; at B, (40, 160) MPa. Find safety factors A and B using available major-principal-stress strength divided by applied major stress.
At A, failure strength is 4×10+28=68 MPa, so factor 68/90≈0.7556. At B, it is 4×40+28=188 MPa, giving 188/160=1.175. Thus D. A lies above the strength line and has factor below 1; B is below it and has factor above 1.
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