Department of Mining and Mineral Processing EngineeringMidlands State University

College Of Applied Sciences, Manicaland

Rock Mechanics (HMIE311)

Assignment 1

Issued: 14 October 2015 Due: 22 October 2015 @9am

1. Give a general description, essential features and general principles of/in Uniaxial Compression (UCS) Test and Tri-axial Compression Test (20)

2.

3. A delta rosette (strain measuring instrument) gives the following strain readings.

ε0 = 11 * 10-4

ε60o = 14 * 10-4

ε120o = -20 * 10-4

Find the magnitude of ε1 and ε2 (principal) strains and the direction (10)

4. Given σx = -15 Mpa, σy = 6 Mpa, τxy = -20Mpa

Calculate σ1 and σ2 and directions

Draw Mohr’s Circle of stresses. (10)

5. Discuss in detail the following engineering properties of rock materialsa. Point Load Strength Indexb. Fracture Toughnessc. Brittlenessd. Swelling (14)

6. Calculate the shear strength of a joint surface where normal stress is 4 Mpa using the Barton Equation if JWS is 50Mpa, JRC is 12, and the roughness angle is at 25 degrees. And if we assume the two surfaces of a joint are not welded together how it is possible for the joint to have cohesion? (6)

7. i) Define: Bulk Modulus, Elastic Modulus and Shear Modulus (modulus of rigidity). (9)ii) Determine the principal strain components and the modulus of rigidity given the

following;

σ1 = 300 Kpa σ2 = 200 Kpa

E = 50 Gpa ν = 0.25 m (6)

8. A haulage-way is to be driven through a limestone zone which has uni-axial compressive strength of 180Mpa and a R.Q.D of 80%. Joint spacing is 0.5m apart; however, the joints are fairly rough and with a separation of millimetres giving a rating of 20. The area is completely dry and the haulage-way is driven across strike of the joints dipping at 15o.a. Calculate the CSIR rating score (5)b. Ascertain the class for this rock mass and describe it. (2) c. What would you recommend as the average stand up time? (2)

9. Write short notes on dry mix and wet mix in relation to shotcrete and state advantages of each system (12)

10. With the aid of sketches describe the briefly each of the following;d. Swellex bolts e. Mat Packs (6)

11. Discuss the following on shear strengtha. Hydraulic pore water pressureb. Graphite as in-fill materialc. Quartzite shear zones as in-fill materiald. Montmorilonite clay as infill wet material ( 8)

Total Marks: 110