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Homework Help: Rock Mechanics: Mohrs Stress Circle - Principal Stresses

  1. Oct 10, 2015 #1
    1. The problem statement, all variables and given/known data
    A series of shear tests were performed on a weak rock. Each test was carried out until the sample sheared, and the principal stresses for each test were:

    S. No.--- σ3 (KN/m2) --- σ1 (KN/m2)
    1 --- 200 --- 570
    2 --- 300 --- 875
    3 --- 400 --- 1162

    Plot the Mohr’s stress circle and hence determine the angle of internal friction and
    cohesion of the rock from Mohr’s envelope. If the confining pressure was 600KN/m2 extrapolate the failure stresses of the rock sample.

    // I've done solid mechanics and have a good idea of Mohrs circle, but im just confused on how its written and dont know how to start and have a few questions:
    - Is the element in plane strees? and is the 2nd principal stress 0?
    - Do i evaluate each sample seperetly?

  2. jcsd
  3. Oct 10, 2015 #2

    Yes. Assume it is.
    No. You evaluate them all together on the same graph.
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