Supports

1. Statement 1 Higher pack resistance is required under a sandstone roof than under a shale roof for equal risk to bending.

Statement 2 Beds of shale have lower bending capacity than sandstone.

a) Both statements 1 and 2 are correct and Statement 2 is the correct explanation of statement 1.

b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1.

c) Statement 1 is correct and statement 2 is incorrect.

d) Statement 1 is incorrect and statement 2 is correct.

c. Beds of shale have higher bending capacity than sst.

2. Statement 1 Goaf control is easier for shale than sandstone. Statement 2 Shale roof frequently occurs in thick beds.

a) Both statements 1 and 2 are correct and Statement 2 is the correct explanation of statement 1.

b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1.

c) Statement 1 is correct and statement 2 is incorrect.

d) Statement 1 is incorrect and statement 2 is correct.

b correct explanation shale roof is easily cavable as compared to a sst roof.

3. State “ True” or “ False”.

Disintegration of shale roof may be due to the softening and

dispersion of the colloidal particles which bind the constituent

particles of shale together.

true

4. The compressive strength of Indian coals varies from

a. 56 to 394Kg/cm2

b. 28 to 56 Kg/cm2

c. 14 to 28 kg/cm2

d. 5.6 to 14 Kg/cm2

a

5. CMRI has classified roof rocks into 5 categories based on RMR

values.

A very good roof (RMR 80 – 100)

a. Needs yielding steel arches as support

b. Needs rock bolting for support

c. Needs only props for support

d. Does not need any support.

d

6. Fill in the blanks

In case of thick strong roofs, thickness of roof is more than

____________ metre(s).

a. 2

b. 1

c. 0.5

d. 0.25 b

7. The following type of roof presents difficulty in caving

a. Thick strong roof

b. Stratified strong roof

c. Fragile roof

d. All of the above a

8. Which of the following roofs is considered treacherous?

a. Sandstone

b. Shale

c. Coal

d. Granite b

9. Which of the following is not considered as a factor to estimate RMR for roof

support by CMRI

a. Layer thickness

b. Strength of rocks

c. Ground water flow

d. Width of excavation

d

10. Which of the following is not an advantage of concrete as a supporting

material over timber and steel?

a) It is not affected by atmospheric conditions and has a long life.

b) It has a very high tensile strength.

c) It gives smooth surfaces and hence resistance to air current is minimum.

d) It has a long life.

b

11. Fly ash obtained from power plants is an important addition to concrete. It serves the

function of

a. Decreasing the curing time of concrete.

b. Increasing the setting time of concrete.

c. Increasing the fluidity of concrete in pipeline transportation.

d. Increasing the quantity of the mixture.

c

12. In the wet – mix process of shotcreting –

a. The major constituent of shotcrete is water.

b. Water is sprayed over the wall after a dry mixture of sand and cement

has been projected over it.

c. All the ingredients are mixed before they enter the delivery hose.

d. A mixture of cement and damp sand is conveyed to the nozzle where

water is added.

c

13. Calculate the thickness of shotcrete required to support a gallery of radius 3m according to Rabcewicz formula which is given by –

Where, t = thickness of concrete in meters r = radius of the gallery in meters = allowable shear strength of the shotcrete material (t/m2) P = stress on the shotcrete(t/m2)

Given that P = 15 t/m2 and Assume an FOS of 3.

Ans 0.13m

14. Which of the following statements is not correct?a. Compressive strength of concrete decreases with the porosity.b. The strength of concrete first increases to a maximum and then starts to

decrease with an increase in the water – cement ratio.c. Higher temperature increases the setting time while lower temperature

fastens the process of curing.d. The amount of water needed depends on he granulometry of the aggregates

and the compressive strength desired.

c

15. The dry mix system tends to be more widely used in mining than wet mixed shotcrete because –

a. Wet mixed shotcrete will increase the humidity of the underground environment.b. Wet mixed shotcrete takes less time in preparation and application.c. Dry mixed shotcrete lacks strength to withstand high stress concentrations at great

depths.d. The dry mix system uses a smaller and a more compact equipment which can

move around easily an underground mine environment.

d

16. Silica fume is widely used in the shotcrete mixture. The reasons being-I. It increases the strength of shotcrete by 2 – 3 times.II. It increases flexural strength and improved bond with the rock mass.III. Layers upto 200mm thick can be placed in one pass because of shotcrete’s

stickiness.

a) Only Ib) Both I and IIc) All of the aboved) Both II and III

c

17. In very poor rock masses with loose rocks , the most preferred support would be –a) Systematic roof bolts.b) Mesh reinforced shotcrete.c) Steel fibre reinforced shotcrete.d) Hydraulic props

b

18. Chainlink mesh ( fig.i) , though strong and flexible is not suitable for shotcrete application and welded wire mesh (fig ii) is a better option because -

a. The chainlink mesh can not have good contact with the rock surface.b. The mesh can collapse under its own weight instead of providing support because of

greater amount of steel wires used.c. Welded wire mesh uses better quality steel.d. It is difficult for the shotcrete to penetrate the chainlink mesh.

d

iii

19. Mention any one kind of wood used as a support in Indian coal mines.

Ans-Say one of the following

Sal wood, teak wood, sankhon wood

20. State “TRUE” or “FALSE”

“Load bearing capacity of prop increases with an increase in the L/D ratio.

false

21. Which of the following is not a factor affecting the load bearing capacity of the props –a. Length to diameter ratiob. Eccentricity of the propc. In situ stress conditions present in the rock stratad. Moisture content

c

22. Name a device used to withdraw props.

Say one of the followingSylvester prop withdrawer, Monkey winch, Power driven winches

23. According to CMR the lid over a prop shall have a width not ___________ (less/more) than the diameter of the prop, thickness not less than ______ cm and length not less than _____________ cm.

Ans less, 8, 75

24. According to CMR the length of the cogging members should not be less than –a. 0.8mb. 1.0mc. 1.2md. 1.4m

Ans c

25. Which of the following is not an advantage of timber supports?a. The crushing of timber becomes apparent long before it breaks,b. It is resistant to fungi, bores and insects.c. It can be easily cut, manipulated and transported.d. They are relatively cheap

Ans b

26. Artificial supports perform which of the following functions ?

a. They hold loose rocks, key blocks and other supports in place.b. Reinforce the rock mass and control bulking.c. Retain broken or unstable rock between the holding and reinforcing element to

form a stratified archd. Al of the above.

Ans d

27. Which of the following locations is most preferred to erect a square chock?a. At faceb. At junctionc. At drive head of conveyorsd. In permanent roadways

b

28. An underset prop is a – a. Tapered propb. Pit propc. Prop whose axis remains in between the vertical and the normal to the seamd. Prop whose axis is normal to the dip of the seam

c

29. Statement 1 Yielding props are now-a-days exclusively used on longwall faces and rigid props are non-existent.

Statement 2 Withdrawal of yielding props is quite easy unless these props have gone solid.

a) Both statements 1 and 2 are correct and Statement 2 is the correct explanation of statement 1.

b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1.

c) Statement 1 is correct and statement 2 is incorrect.

d) Statement 1 is incorrect and statement 2 is correct

Ans a

Q Q

P30.

The above figure shows the working principle of a friction prop. If Q is the normal force provided by the clamps and µ is the coefficient of friction between the clamp and the upper member. Calculate the bearing capacity P of the friction prop.

Ans 2Q µ

31. The first true walking support was invented by A)Winkhaus B) Allen C) Gullick Dobson D) Marrel Hydro

a

32. Chock shield supports can be applied in seam gradients up to ______ angle. A)40 B)50 C)60 D)70

d

33. ______ is used when roof is of lighter weight , support with shorter base length and lower cost is preferred ? A)Two leg shield support B)Four leg shield support C)Frame type of support D)Chock type of support

a

34. ) Frame type of powered supports can work in seams of ______m thick. A) 1m – 4m B) 0.5m - 1m C) 0.91m – 1.82m D) 1.5m – 3m

c

35. ) Chock type supports give roof loading densities of about ______ on setting and about ______ at yield. A) 18.3tonnes/m2 , 52.5tonnes/m B) 25tonnes/m2 , 65tonnes/m 2

C) 40tonnes/m2 , 60 tonnes/m2

D) 10.8tonnes/m2 , 30.5tonnes/m2

a

36. The average load bearing capacity of wooden props is given by the expression (L= load bearing capacity, h= height of prop, d= dia of prop A) L=h/d B) L=2h/d C) L=H/2d D) None of the above

a

37. Eccentricity of the prop is defined as the maximum deviation of the natural axis of the props from its longitudinal axis expressed as percentage of the length of the prop. (TRUE OR FALSE)

true

38. Higher the length to diameter ratio of the wooden prop , higher the load bearing capacity. (TRUE OR FALSE)

false

39. ) The conventional shield support differs from the chock shield is that its yield requirement is for a given roof load density. (TRUE OR FALSE)

true