Ground Control Mining Engineering

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QUESTION 1

If the horizontal stress is too high for the compressive strength of the rock, and the horizontal stress is 1.8 times higher than the vertical stress, this will probably result in

		floor heave an/or buckling of the back
		hourglassing of the pillars
		pillar failure
		sagging of the back

QUESTION 2

Assuming a rock density of 2800 kg/m3, calculate the stress at the lower corners of a square haulageway driven at the bottom of the shaft. Assume the stress field is hydrostatic.

QUESTION 3

A highly fractured section of AQ core ( diameter = 27.0 mm) was recovered. If the volume of the

core was 444.4 cm3, determine what the length of the core

would have been if it were not fractured.

QUESTION 4

Calculate the vertical stress acting at the bottom of the TauTona Mine (or Western Deep No.3 Shaft) in South Africa. The mine bottom is estimated to be at a depth of 3 .9 km

and the mass density of the rock is 2700 kg/m3..

QUESTION 5

What is the difference between a rock and a rock mass?

QUESTION 6

A rock core fails at a load of 27,500 lb. The diameter of the rock is 1.78 inches, and its length is 3.96 inches. Calculate the uniaxial compressive strength of the rock in psi. Show your calculations.

QUESTION 7

Explain the difference between Pressure and Stress.

QUESTION 8

A highly fractured section of HQ core (diameter = 63.5 mm) was recovered. If the specific gravity of the rock was 2.90, and the section of core weighed 543.5 grams, determine what the length of the core would have been if it were not fractured.

QUESTION 9

If a 12.0 cm rock core stretches by 2mm, when stressed, calculate the strain in the rock.

QUESTION 10

The presence of water in interstices or pores of the rock ________________ its strength.

QUESTION 11

A rock fails at a stress of 234 MPa. The strain at failure is 0.065 %. Calculate the modulus of deformation of the rock.

QUESTION 12

A rock has a transverse strain of 0.004 and a longitudinal strain of 0.013 Calculate Poisson’s ratio for the rock.

QUESTION 13

Given the following information, complete the follwing Table and calculate the total rating number, class of

rock, cohesion, internal angle of friction and anticipated stand-up time for this rock mass.

Rating:

_____ RQD = 87%

_____ compressive strength = 110 MPa

_____ spacing of joint sets = 1.4 m

_____ slightly rough surfaces, separation < 1 mm highly weathered

walls

_____ 0.5 l/min inflow per 10m

drive of tunnel is parallel to the strike of joint set and

_____ dip of major joint set is 15°; drive is against the dip

QUESTION 15

A cylindrical specimen of rock, 60 mm in diameter and 150 mm long is subjected to an axial compressive force of 6 kN. Find:

The normal stress σ_nθand shear stress τ_θ on a plane inclined at 40° to the radial direction.

The maximum value of shear stress.

The inclination of planes on which the shear stress τ_θ is equal to one-half τ_θ _max.

QUESTION 17

The following lengths were recovered from a 3.00 m run of core drilling:

15, 16, 15, 24, 23, 22, 23, 13, 2, 11, 5, 41, 2, 32, 27, 3 cm

a) Calculate the % recovery

b) Calculate the RQD

QUESTION 18

When stress is measured more than ____________________ radii from the centre of an underground excavation, there is no extra stress (due to the presence of the

nearby excavation) added to the normal field stress

		1
		3
		5
		10

QUESTION 19

A 7 m span underground for a haulageway in a mine is to be excavated in andesite at a depth of 1,000 m below surface. The rock mass contains two sets of joints controlling stability. The joints are smooth and planar. RQD is 72% and laboratory tests on core samples of intact rock give an average uniaxial compressive strength of 70 MPa. The principal stress directions are approximately vertical and horizontal and the magnitude of the horizontal principal stress is approximately 1.3 times that of the vertical principal stress ( vertical stress is 26.7 Mpa at this depth). The pressure of the water inflow is 4.0 (kgf/cm ²). Calculate the RQD, J_n , J_r , J_a, J_w, SRF, Q, D_e, Class of Rock and support requirements for this rock mass.

QUESTION 20

A flat piece of slate with uniform thickness 20 mm is cut into the shape of a square with 100 mm long squared edges. A test is devised which allows uniform compressive stress σ₁ to be applied along two opposite edges and uniform tensile stress σ₂ along the other two opposite edges. The stresses σ₁ and σ₂ act normally to the edges of the test specimen. The test is performed by increasing the magnitudes of σ₁ and σ₂ simultaneously, but keeping the magnitude of σ₁ always three times the magnitude of σ₂. If failure of the slate occurs when the shear stress on any plane exceeds 1.2 MPa, calculate σ₁ and σ₂ at the moment of failure.

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