Geology 306 - Study Guide - Exam III

1. Given that the maximum principal stress is 500 MPa and that the minimum principal stress is 100 MPa, can you determine the shear and normal stress on a plane oriented 30 degrees to the maximum principal stress?

2. Given the following equation would a maximum principal stress of 700 MPa and and a minimum principal stress of 300 MPa represent a stable condition? t = (0.3*sn) + 0.25.

3. Can you sketch a stress-strain graph that would be typical of a plastic material? Can you label the yield stress and explain its significance?

4. Can you sketch a stress-strain graph that would be typical of an elastic material?

5. Can you sketch a stress-strain graph that would be typical of rock exhibiting strain hardening? Can you label the elastic limit?

6. Can you tell me why strain hardening (also referred to as work hardening) occurs?

7.Can you tell me what strain softening refers to?

8. Can you derive the 2D equations for normal and shear stress?

9. Given a set of data derived from a triaxial stress test, could you plot the results as a series of Mohr circles? Could you sketch in and explain the Mohr failure envelope?

10. Can you tell me what a Mohr circle represents?

11. Given the equations for shear and normal stress, can you rearrange them into an equation representing a circle?

12. Can you tell me how elongation and stretch differ?

13. Can you tell me how angular shear strain (w) differs from shear strain (g)?

14. Can you derive the 2D strain transformation equation for plane strain simple shear?

15. Can you derive the 2D strain transformation equation for plane strain pure shear?

16. If you distort a circle by plane strain simple or pure shear, then what new geometric shape does the circle change into? Can you tell me the structural name of this new geometrical shape? Can you tell me the name of the long and short dimension of the new geometrical shape?

17. During progressive simple shear, what happens to the principal strain axis X and the principal strain axis Y?

18. During progressive pure shear, what happens to the principal strain axis X and the principal strain axis Y?

19. Can you tell the significance of the term no finite longitudinal strain, and how it relates to the strain ellipse?

20. Can you describe the displacement field for plane strain pure shear?

21. Can you describe the displacement field for plane strain simple shear?

22. Can you tell me the significance of chocolate-tablet boudinage?

23. Can you define "neck-line" for me?

24. Can you define boudinage for me?

25. Can you tell me what a boudin is?

26. If I gave you a geologic map with a set of observations made at different locations could you complete the map and draw a cross-section across it?

27. Given a conjugate set of strike-slip faults striking N30W and N30E can you determine the generalized stress field under which they formed?  Note that the N30W striking set displays dextral offset while the N30E set exhibits sinistral offset.

28. Could you plot the above results along the attitudes of the two fault sets in lower hemisphere equal area space?

29. What would be the general orientation of folds, reverse vaults, and normal faults under the conditions stipulated in questions 27 and 28?

30. Why do you think fault zones are commonly modeled as zones of simple shear?