Download 10 Marks

EXAMINATION PAPER
SUBJECT:
EXAMINER:
STRATA CONTROL CERTIFICATE COAL
SUBJECT CODE:
L MUNSAMY
MODERATOR:
B MADDEN
EXAMINATION DATE: OCTOBER 2008
TOTAL MARKS: [100]
TIME: 09h00 – 12h00
PASS MARK: 60%
NUMBER OF PAGES:
4
SPECIAL REQUIREMENTS:
1. Answer ALL FIVE questions
2. References other than those provided are not permitted.
3. Hand-held electronic calculators may be used.
4. Put your examination number on the outside cover of each book used and on any graph
paper or other loose sheets handed in.
NB: your name must not appear on any answer book or loose sheets.
5. Write in ink on the RIGHT HAND SIDE of the paper only (only the right hand pages
will be marked).
6. Show all calculations on which your answers are based.
7. Illustrate your answers by sketches or diagrams wherever possible.
8. In answering these questions, full advantage should be taken wherever necessary of your
practical experience as well as of the data given.
9. Answers must be given to an accuracy that is typical of practical conditions.
Question 1: (10 Marks)
Define the following Rock Engineering Concepts and give their units of
measurement
1.1 Force
1.2 Tri-axial Test
1.3 K- Ratio
1.4 Fracture Frequency
1.5 Principal Stresses
(10)
Question 2: (20 marks)
2.1 Briefly explain with the aid of sketches the following roof support principles:
a) Suspension
b) Beam Building
(4)
2.2 The following data was obtained from Short Encapsulation Pull Tests that you
conducted underground at your mine. Note that this data has been calibrated to take into
account the stretch in the steel.
Load (kN)
Deformation
(mm)
0
10
20
30
40
50
60
70
0
0.2 0.35 0.4 0.5 0.65 1.2 1.55
80
90 100 110
2.5 3.5
6
8
USE THE GRAPH PAPER IN THE MIDDLE OF THE ANSWER BOOK TO CONTRUCT
THIS GRAPH
a) Construct a load deformation graph of the data.
(5)
b) Briefly discuss the difference between soft and stiff support. Use graphs to
explain your answer.
(4)
c) Briefly discuss the pull test results above. Would these results be adequate for
the ground conditions you have at your mine.
(4)
d) Discuss the changes that you would implement to change the stiffness of the
bolting system as described by the pull test data above.
(3)
120
10
Question 3: (15 Marks)
Selebi Colliery plans to mine 2- seam in the Witbank Coalfield and has requested that
you assist them with the roof support system to be implemented.
The 2-seam to be mined is 4.2m thick and it is planned to be mined by bord and pillar.
The bords are planned at 6.5m wide. The roof above the 2-seam consists of:
-
0.15m thick fossil marker (shale), overlain by
-
1m of sandstone, overlain by
-
3m of shale/sandstone
3.1 Using 16mm diameter bolts installed in a 25mm diameter hole, with full column resin
and pre-tensioned to 50kN, determine the bolt density i.e. number of bolts in a row and
row spacing required to achieve the desired support resistance. Make assumptions
where necessary and show all calculations.
(7)
3.2. Evaluate your theoretical bolt density calculation. Is it adequate to reinforce the
roof?
(3)
3.3 If you had to make changes to the bolting system, what would they be and why?
(5)
Question 4: (10 Marks)
Manto Colliery is mining 5 seam with a 7 road mechanised bord and pillar layout. The
layout dimensions are as follows:
-
Pillar width is 6m
-
Bord width is 6.5m
-
Heading distance is 12m
-
Mining Height is 2.1m
-
Depth Below surface is 45m
-
Intake ventilation is on the right hand side.
5.1 Calculate
a) The safety factor (Salamon and Munro)
(5)
b) The CM adjustment safety factor
(5)
Question 5: (25 Marks)
As a strata control officer on an Opencast Operation you have been asked to present the
different rock mass classification systems conventionally used in open pit mining to
management who have a limited understanding of these tools.
5.1 Discuss at least three rock mass classification systems you are familiar with.
(10)
5.2 Discuss which system is most suited to your mine and why.
(2)
5.3 What are the common failings with these systems
(3)
5.4 If you were to develop your own rock mass rating system, briefly describe
the parameters that you would include and why.
(5)
5.5 Jointing in rock affects the strength of the rockmass. Briefly describe the effect of the
following on joint strength:
a) Infilling type
b) Infilling Thickness
c) Joint Roughness
d) Joint Friction Angle
e) Effect of water on joints
(5)
Question 6: (20 Marks)
Mashiyi Colliery uses 20mm diameter x 1.2m long bolts resin grouted roofbolts as
standard support. The support holes drilled are 26mm in diameter. 23mm diameter x
500mm long resin capsules are used to grout the holes.
6.1 Calculate the hole volume.
(3)
6.2 Calculate the bolt volume
(3)
6.3 Calculate the annulus volume.
(2)
6.4. Determine the number of resin capsules required to achieve full column resin
grouting.
(5)
6.5 If this was a point anchor installation with ONE (1) capsule of 23mm diameter x
500mm fast resin was used, what would be the length of the ungrouted part of the bolt?
(7)
Strata Control Formulae
S  7,2
L
w 0, 46
h 0,66
25 H C 2
w2
   o (1 
2w0 2, 46
)
w
pgt
n=SF ------Pf
Lb 



d c2 Lc
D2  d 2
Pf
 . D . Lb
 L4
23 E t 2
 L2
2t
FS  288
w 2.46
Hh 0.66 ( w  b) 2
R00.5933 0.5933 R 
 s  7.2 0.0667 {
[( )  1]  1}

Ro
V