confining pressures (Table 2). In each case, the rock sample failed when the differential
pressure reached a value > 420 MPa. Examination of the core samples showed that failure
occurred by ductile shear along a small shear zone oriented at a consistent angle to 0₁. Using
the data in Table 2, draw a second set of Mohr circles for these experimental runs. Next, draw
a failure envelope tangent to the four Mohr circles and draw a Mohr radius for each circle
using the point of tangency. Estimate the angle a of the shear zones relative to 0₁. What is the
significance of the intersection between the Coulomb and ductile failure envelopes?
Fig: 1
Fig: 2