This document discusses roof support in underground coal mines. There are two main types of roof support: intrinsic supports like roof bolts that are installed within the roof, and standing supports like timber props that are installed between the roof and floor. Timber supports are commonly used in Indian coal mines due to low cost and availability, though metal supports offer higher load capacity. A case study examines how roof bolts were used with a specific layout and spacing in the Tandshi coal mine in India. Proper roof support is necessary to prevent roof collapse and protect miners from rock falls.

1. ROOF SUPPORT
IN
UNDERGROUND COAL MINES

2. CONTENTS
▪ INTRODUCTION
▪ NEED FOR SUPPORT
▪ TYPES OF SUPPORT
▪ STANDING SUPPORT
▪ INTRINSIC SUPPORT
▪ CASE STUDY
▪ REFERENCES

3. INTRODUCTION
▪ Every underground mine can be subjected to roof failure.
▪ It has been the major cause for fatalities to mine workers across
the world.
▪ Therefore, roof supports are used to stabilize the roof.
▪ Roof supports include both intrinsic supports, such as roof bolts,
and standing supports, such as timber.
▪ They interact with the ground to create a stable rock structure.

4. WHY ARE SUPPORTS NEEDED?
▪ To prevent major collapses of mine roof.
▪ To protect miners from small rock falls that can occur from the
immediate roof skin.
▪ To prevent deformation of mine openings for access, escape
and ventilation of mine workings.
▪ To safeguard expensive machines used in mines.

5. TYPES OF SUPPORT
▪ Intrinsic support –The supporting system in which the
elements are installed within the roof.
e.g. – roof bolt, cable bolts, metal pins etc.
▪ Standing support –The supporting system in which the
elements are installed between the roof and floor.
e.g. – wooden logs, metal rods, steel arches etc.

6. STANDING SUPPORT
▪ TIMBER SUPPORTS
▪ METAL SUPPORTS
▪ POWERED SUPPORTS
▪ STEEL ARCHES

7. TIMBER SUPPORTS
▪ Timber supports are very common in Indian coal mines as it is
cheap and easily available.
▪ Over 90% of underground coal output comes from timber
supported workings.
▪ The kind of wood used as support in Indian coal mines are sal
wood, teak wood, sankhon wood etc.
▪ Timber supports can be:Timber Props,Timber Bars and
Wooden chocks

8. TIMBER PROPS
▪ The timber prop is strongest when the load acts parallel to its
length.
▪ In flat seams the prop is erected vertical, and in vertical seams,
the axis of the prop should be normal to the dip of the seam.

9. (image reference: https://www.undergroundminers.com/timbermethods.html/

10. TIMBER BARS
▪ Bars act as beams.
▪ If the sides are weak, the bar is placed on vertical props.
▪ The bar should always be tight against the roof and should offer
maximum area of contact against it.
▪ The side of the bar towards the roof is chopped flat for this
purpose.

11. (image reference: https://www.undergroundminers.com/timbermethods.html/

12. WOODEN CHOCKS
▪ A chock, cog or chockmate is a combination of sleepers above one
another in a criss-cross manner.
▪ It supports a much larger stretch than a prop and is used in places
where the roof is bad over a wide area and needs a substantial
support.
▪ They are also erected where main roadways have to pass through
area having coal pillars of inadequate size.

13. (image reference: https://www.olivesawmills.au/-mining.html/

14. PROS AND CONS OF TIMBER SUPPORTS
▪ Advantages:
 They are relatively cheaper.
 They are easily available.
 They can be cut easily into desired length.
 They give early warnings when they swallow.
▪ Disadvantages:
 The resistance offered by timber is not uniform. Hence, it is difficult to standardise the
design of support system.
 They may have inherent defects which will reduce the load bearing capacity considerably.
 The yield of timber is relatively low.

15. METAL SUPPORTS
▪ Iron and steel have been used in mines in the form of rigid and
yielding props, beams and girders, reinforcement in concrete
and corrugated sheets.
▪ FRICTION PROPS
▪ HYDRAULIC PROPS
▪ POWERED SUPPORTS
▪ STEEL BARS

16. FRICTION PROPS
▪ They are early bearing props and accept the roof and load very
quickly.
▪ They have constant load yield characteristics.
▪ Friction props were adopted on longwall face with sand stowing
first time in Chinakuri colliery.

18. HYDRAULIC PROPS
▪ A hydraulic prop is simply a hydraulic jack.
▪ They have been used at longwall mechanised faces in our
country.
▪ A hydraulic prop can be set to take immediately 3/4th of the
maximum load but when overloaded it will yield at the designed
load after which the resistance is uniform.

19. (image reference: https://www.chinacoalintl.com/pd-711)

20. PROS AND CONS OF METAL SUPPORTS
▪ Advantages:
They can be easily re-used.
They have high load carrying capacity.
▪ Disadvantages:
They are relatively more expensive than timber supports.
They do not give early warning signs as timber.
They can get corroded due to moisture and mine water.

21. ▪ Powered supports enables the cutting machine to be used in full
capacity as they can be moved forward fast enough to keep
pace with any modern face cutter.
▪ Thus, they enable rapid advance of the face which in turn brings
about improvement in roof conditions at the face.
POWERED SUPPORT

22. SELF – ADVANCING OR WALKING SUPPORT
▪ These are open circuit type hydraulic chocks which, when
already erected at a place, can be retracted by hydraulic
pressure, pushed to the new site of erection by hydraulic
shifting cylinders and erected by hydraulic pressure
▪ A workman is not required to handle the supports during any of
its processes, except for guiding the roof bars supported by the
hydraulic props.
▪ The self-advancing supports are used in coal mines on prop-free
front of longwall faces and were introduced first time in India in
Moonidih colliery, BCCL.

24. SHIELD SUPPORT
▪ The shield supports provides a continuous cover all along the
face by canopies placed side by side.
▪ It is like a multi-leg hydraulic chock support except for a little
difference in construction at the rear side, i.e., goaf side.
▪ The shield supports are with four legs which react directly with
the canopy.
▪ It is suitable for sub-level caving in thick seams or for
conventional operations in longwall faces.

26. STEEL ARCHES
▪ They are used for supporting permanent and semi-permanent
roadways.
▪ Heavy section rails in two parts are suitably shaped to form an
inverted U when assembled together.
▪ They have no yielding property.
▪ To keep arches in contact with the roof and sides wooden
laggings are placed on top and sides.

28. INTRINSIC SUPPORT
▪ ROOF BOLTING
▪ ROOF STITCHING
▪ WOODEN DOWEL
▪ BAMBOO BOLTING

29. ROOF BOLTING
▪ Roof bolting is the practice of drilling vertical holes in the roof and
fixing steel bolts into the in a manner that the bolts grip the strata
and support the immediate roof.
▪ The bolted roof strata behave as one thick seam capable of
supporting not only their own weight ut the weight of the strata
above them.
▪ They are of two types:
1) Slot and wedge
2) Expansion shell

31. PROS AND CONS OF ROOF BOLTING
Advantages:
▪ It is simple to apply, easy to mechanise and moderately cheap in
cost.
▪ It gives greater headroom and clearance in the roadway.
▪ Storage space required is small.
Disadvantages:
▪ It can not be applied in all cases.
▪ It gives no warning signs of impending failure.
▪ Some types of bolts are not recoverable. e.g. slot and wedge bolt

32. ROOF STITCHING
▪ The principle of roof stitching is the same as that for roof bolting,
i.e., the immediate rocks are held together as a composite stratum of
large thickness.
▪ Roof stitching was adopted in coal mines as well as metal mines at
Balaghat and Seetharama mica mine. It cannot be used in mines
where roof condition deteriorates immediately after blasting.
▪ This method of support is both effective and cheap.

34. CASE STUDY OF TANDSI MINE, WCL
▪ Rock Mass Rating(RMR) = 44-64
▪ Roof was supported by roof bolts up to 1.5 m length
▪ Gallery width = 4.5 m
▪ The roof bolts were installed such that there were 3 bolts in each row.
▪ The bolts had a spacing of 1.5 m from each other and 0.75 m from the
pillar.
▪ One of the bolts was drilled vertically. And the other two were drilled
inclined in such a way that they went into the pillar there by
supporting the overburden pressure.

35. Design of layout for roof bolting
(image reference: Sudipta Mukhopadhya and Satish Sharma (2017), A case study illustration of
the layout and support in an Indian coal mine.)

36. REFERENCES
1. D.J. Deshmukh, Rock Mechanics and Roof Supports. Elements of
MiningTechnologyVol.1.
2. R.D. Singh, Strata Control in Coal Mines. Principles and Practices of
Modern Coal Mining.
3. Christopher Mark andThomas M. Barczak, Fundamentals ofCoal
Mine Roof Support.
4. https://www.kau.edu.sa/, Mine Support.
5. Manoj Kumar Biswal, Design of Support System for Bord and Pillar
Workings.
6. https://www.stolajohannes.cz/, Mine Supports.
7. https://www.cdc,gov/, Roof Support.