Question 1. Define rock mechanics. Discuss the main objectives of the application of rock mechanics in mining.
Question 2. Define stress. Draw a diagram and define the normal and shear stress by resolving the resultant force vector acting on any infinitesimal plane into its two Cartesian (x, y) components. The following diagram gives the state of stress at a point in two dimensions and on an oblique plane:
If σx = 12.5 kPa, σy = -13.0 kPa, τxy = 8 kPa and θ = 250. Determine the magnitudes of the normal and shear stress components on the oblique plane shown in the above figure.
Question 3. Define Principal Planes and Principal Stresses. At a point within a body σx = - 8.5 kPa, σy = 5.0 kPa, τxy = 1.5 kPa. Draw the element with the given stress components. Determine the orientations of the principal planes and the magnitudes of the principal stresses with correct senses.
Question 4. Discuss in general the geo-mechanical background to the slope instability problem.
Question 5. What are the inherent complexities of rock?
Question 6. Given are the major and minor principal stresses at any point within a rock mass
σ1 = 50 MPa and σ3 = 20 MPa
Determine graphically the magnitude of the stress components acting on a plane that is inclined at an angle of 250 to the major principal plane.
Question 7. Define the followings:
1) Rock material, rock mass and rock structure.
2) Dip, true dip, dip direction and strike
Question 8. What are the major properties of defects within a rock mass from an engineering perspective?
Question 9. Analyse the sliding of a rock block on an inclined plane from the limiting equilibrium perspective for the cases as outlined in the following figure.
a) sliding due to gravitational loading
b) the effect of water pressure in a tension crack that separates the rock block from the rock mass and also at the contact surface with the inclined plane
c) reinforcement of the rock block to prevent it sliding
Question 10. What are the different types of slope failure for rock slopes? Explain with proper diagrams.
Question 11. What do you understand by triaxial constants of rock mass? How these can be determined in the laboratory.
Question 12. Explain the Brazilian test to determine indirect tensile strength of rock mass.
Question 13. Draw a typical complete stress-strain curve for rock under uniaxial compressive loading and explain the distinct zones in the curve. What is strain softening of rock?
Question 14. For the slope shown in the diagram below the following is known:
- Average planned slope angle, i = 650
- Angle of discontinuity from the horizontal β = 410
- Angle of internal friction φ = 300
- Cohesion, c = 1.6 kN/m2,
- Unit weight (density) = 1875 kg/m3
- H = 50m and B = 35m, assume unit thickness (1m) for rock block.
Determine the factor of safety for the slope assuming drained conditions.
Question 15. A mine is planned to use a decline with a dip of 300 to access the ore-body at the depth of 500 meter. Estimate the vertical and horizontal insitu stresses at 500m depth, assuming the average unit weight of rock 27 kN/m3, horizontal Young's modulus 75 GPa and Poisson's ratio 0.3.
Question 16. Why is rock mechanics instrumentation so important at every stage of construction of a structure in rock?
Question 17. Explain the Q system and RMR system of rock classification.
Question 18. Enumerate various indirect methods to determine compressive strength of rock. Explain Point Load Index test in detail with proper diagram.
Question 19. Discuss the different types of surface subsidence that can occur and describe the important characteristics of each.
Question 20. For a longwall coal-mining situation what do subcritical width, critical width and supercritical width with regards to subsidence mean?
Question 21. Define the term's active and passive rock support. Describe examples of each type of support.
Question 22. Briefly describe the construction, installation and support methodology for the various rock bolting technologies available to the mining industry. Also define limitations of use for each system.
Question 23. A cavern 165m long, 22m wide and 15m high is to be excavated in chalk beneath the sea. The crown of the cavern will be 35 m below the seabed. What is the main geological information you would like to have before proceeding with the excavation?