Roof Bolting AKM

Prof (Dr) A K Mishra

Indian School of Mines

Physical Properties

Shape & Size

The Roof bolt shall be of MS Steel or TMT Rebar having circular

cross-section with ribs on circumferential region.

The design, calculations, Yield Strength and Ultimate Tensile

Strength along with elongation at Yield and the factor of safety of

the roof bolt has to be defined clearly.

Length

Length of the Roof Bolt shall not be more the designed length + 5mm

StraightnessThe roof Bolt shall be straight without any joint, welding, deviation or

deflection.

In case of deflection and deviation cannot avoided due to practical

reasons, it shall not be more than + 0.1 % per meter length of the bolt.

RibThe Rib of the Roof Bolt shall be as per the design of the rib with an

objective to maximize the surface area without reducing the core

diameter of the roof bolt and having maximum grip with the grout.

the height of the rib shall be kept within the standard prescribed in IS

1786 – 2008 or BS 7861 (Part 1) 1996 or latest revision thereof.

Physico-mechanical Properties

Steel for the Roof Bolt

The roof bolt shall be of thermo-mechanically treated

(TMT) rebar manufactured from MS Grade Fe-500, Fe-

600 or above.

The minimum load bearing capacity (Anchorage Load) of

the roof bolt shall be 160 kN.

The Yield Stress, Tensile Strength and % elongation steel

Grade shall be maintained as per the IS 1786 and IS

13920.

Chemical Composition

Chemical composition of the steel for manufacturing of the roof bolts

varies according to the requirement of strength characteristics and

specific applications.

Certain chemical constituents of the steel which influence the required

properties of steel are

Sl. No. Constutuent Percentage by weight

1 Carbon © 0.25 (Max)

2 Sulfur (S) 0.05 (Max)

3 Phosphorous(P) 0.05 (Max)

4 Manganese 1.5 (Max)

5 Other Alloying/micro

alloying elements

0.50 (Max)

Thread on the Roof Bolt

The thread on the roof bolt shall be M20 cold rolled thread

conforming to IS 4218 (part- 2 & 3) and no cut thread shall be used.

The minimum length of the thread shall be 150 + 5mm and the

tolerance class designation of 8g.

The thread shall conform to tolerance class of 7H.

As a routine test, one thread in every 50 produced shall be checked

using a go/no-go gauge.

Non-threaded end

The non threaded end of the rock bolt shall be formed by cropping or

sawing.

It shall be free from burrs and edges which protrude beyond the

profile of the rock bolt.

Nut

The Nut shall be of hexagonal shape of thickness not less than 30mm

conforming to IS 1363 (Part-3) and the thread shall conform to

tolerance class of 7H.

Pull Test

Thread and the Nut on the roof bolt shall be subjected to pull test

which should not slip at the yield strength/load of the roof bolt.

The anchorage strength of roof bolt is determined for generally

check, that the rock bolt can sustain the specified conditions in pre-

specified load conditions of rock strata.

As per DGMS, the anchorage and setting time relation is

Sl. No. Setting Time Anchorage (Te)

1 30 min 3

2 2 hrs 5

3 24 hrs 10

4 28 days 12

Bearing Plate

The Bearing Plate of the roof bolt shall be Dome Washer Plate of

dimension 150 x 150 x 8 (minimum) mm with compatible central

hole of required size and angled side to ccommodate the conical seat

and nut.

The minimum load at which the Domed Washer Plate will become flat

should be at least 14 Tonnes.

Conical Seat

Conical Seat shall be of forged steel of required dimension.

The Conical Seat shall not deform at 1.20 times the Yield stress of the

roof bolt.

Tensile Test of the Roof Bolt Assembly

The Roof Bolt Assembly shall be subjected to Tensile Test and should

not fail up to 16 Tonnes load.

Weatherability

The Roof Bolts and its components or parts shall be subjected to

Accelerated Weathering Test in mine water condition for 20 days.

No deterioration should occur on the Assembly.

Accelerated Weathering Test shall also be conducted in acidic water

condition for 20 days during which no deterioration should occur on

the Assembly.

Corrosion Resistance Test

The Roof Bolt Assembly shall also be subjected to Field Exposure

and Corrosion Resistivity Test as per IS- 5555: 1970

It is to test the resistance to corrosion of the steel of the roof bolt and

its parts.

SAMPLING & TESTING

To check the composition and required parameters during

manufacture, random sampling be done @ of 2 roof bolts per 1000

pieces of roof bolts and its accessories.

Shall be signed by the persons carrying out the test and shall be

countersigned by the quality control officer posted at the

manufacturing unit(s).

• The user shall carry out Physical examination tests as far as

possible but shall conduct Tensile Test of the Assembly for every

batch of Roof Bolts & its Accessories.

• In case the Roof Bolts or any of its accessories fail to pass the

required tests at the user’s end, that batch or lot of the manufacture

shall not be used in the mine and intimation thereof shall be sent to

the manufacturer.

• The Chief Inspector of Mines or an Inspector of Mines may

Inspect and check

Examine the manufacturing facilities at any time

Get samples tested during the course of inspection

Send such samples for testing at any national test houses/laboratories at the cost

of the manufacturer

May inspect, check and examine the roof bolts and its accessories at any time in

the mine or the area of the mines and get samples tested

• All the Owner, Agent and Manager including the

manufacturers and suppliers shall be required to

comply with this standard and any deviation or defects

found in the product supplied or used in the mine, shall

be bought to the notice of this Directorate.

• Manufacturers and the Users including the Test Houses,

who are engaged for testing of such material, are

therefore requested to ensure the above mentioned

Standard and Parameters before supplying and using at

the mine.

Standards for use of Resin capsule as grouting material

Shape & Size

The measured gel time and setting time of the resin capsule shall conform to

the

Gel Type Setting Time

Fast Set 23 sec to 54 sec

Slow Set 134 sec to 202 sec

Reaction Temperature and Thermal Stability

The reaction temperature and thermal stability of resin capsule shall

conform to

Reaction Temp (oC) Not more than 80

Thermal Stability

At 5 oC for one hr

At 45 oC for one hr

The sample shall satisfy gel

time and setting time

mentioned above

Physico-Mechanical Properties

The physico-mechanical properties of the resin capsule after setting

shall conform to

Sl. No. Properties Remarks

1 Compressive strength: (for slow-set type)

30 min

24 hrs

30MPa (min)

80MPa (min)

2 Bond Strength Test:

30 min

24 hrs

10 Tonnes

15 Tonnes

3 Shear Test 19 MPa (min)

4 Shrinkage Test: (for slow-set type)

24 hrs

7 days

0.01% (max)

0.01% (max)

5 Flammability Test The product should

be of very low

flammability

Rock Bolt Installation

Limited

More versatile

Inexpensive

Costly

Roof BoltingRoof Bolting

• Support Principles

• Support Parameters

• Shotcrete

Bolting Principles

Beam building

Suspension

Keying

Surface control - natural arch

What is the Bolt System Designed to do?

Beam Building

Weak

Strata

Laminated

Strata

Individual laminations

bound together to form a

single beam

Support Principles

SuspensionCompetent

Strata

Weak

Strata

Anchorage

Zone

Support Principles

Suspended layer

Keying

Weak

Strata

Fractured

Rock

Support Principles

Surface Control

Highly jointed, altered or

weathered rock

Support Principles

Critical Parameters

• Bolt Type

• Strength

–Grade

–Diameter

• Length

• Density (spacing)

• Plate

Types of Bolts

Friction Anchored

Mechanical

Fully Grouted

Tensioned Rebar

Combination/Point Anchored

Mechanically Anchored/Resin

Assisted

Support Characteristics

Anchorage

Clamping

Vertical Stiffness

Horizontal Stiffness

Split sets provide minimal support (~1

ton per foot of anchorage) when

utilized in a suspension application.

Friction Anchored Support

Splitsets or Swellex Bolts

Friction anchored bolts

SPLIT TUBE

EXPANDING TUBE

Mechanisms of friction anchor bolts

LOW PLATE LOADS

LOW ANCHORAGE

DEVELOPED ALONG

BOLT LENGTH

NO CLAMP

LOADS

LITTLE OR NO SHEAR

RESISTANCE ALONG

SLIPS AND JOINTS

UNLESS INTERSECTED

BY BOLT

Split Sets

Inexpensive

Easy to Install

No resin cartridges

Can be installed in soft or shifting ground

SPLITSET

RADIAL FORCE

SWELLEX

DYWIDAG BOLT

Friction Anchor Bolts

Critical Parameters

• Bolt Type

• Strength

– Grade

– Diameter

• Length

• Density (spacing)

• Plate

EXPANSION SHELL

ANCHOR BOLT

PARTS OF A BOLT

• SHELL

– STANDARD ( HARD ROOF )

– BAIL ( SOFT ROOF )

• PLUG

– SPREADS SHELL

• SUPPORT NUT (PAL NUT or JAM NUT)

– HOLDS SHELL IN PLACE - THEN BREAKS

AWAY

• WASHER

– ACTS AS LUBRICATION BETWEEN PLATE AND

BOLT HEAD

WHAT DOES GRADE OF

A BOLT MEAN ?

• GRADE 75 MEANS THE BOLT HAS

A TENSILE STRENGTH 75,000 PSI

-TENSION BOLTS

• GRADE 60 MEANS THE BOLT HAS

A TENSILE STRENGTH 60,000 PSI

-NONTENSION BOLTS

WHAT DOES THE TERM

#5 REBAR MEAN ?

• THE DIAMETER OF BOLT ARE

STAMPED IN 1/8 INCH INCREMENTS

• SO A #5 HAS A DIAMETER OF 5/8

INCH

• A CIRCLE AROUND THE NUMBER

MEANS IT IS A DEFORMED BAR

• 5/8 INCH REBAR = 5

ROOF BOLT HEAD

MARKING

5 Grade 55 5/8 INCH

DIAMETER

ROOF BOLT MARKINGS

GRADE DIAMETER DESIGNATION

40 3/4 INCH UP NONE

55 5/8 INCH UP

60 5/8 INCH UP

75 5/8 INCH UP X

100 5/8 INCH UP

Plugs

Shell Leaves

Support Nut

Bolts

Bail

BAIL STANDARD

STANDARD 4 LEAF TYPE

EXPANSION SHELL

THREE PRONG EXPANSION

SHELL

TWO LEAF BAIL TYPE

EXPANSION SHELL

JAM NUT

TO STRONG

• JAM NUT

• TOO STRONG

• ( DOES NOT

• BREAK AWAY

• AND DEFORMS

• THE SHELL )

DEFORMED SHELL

JAM

NUT

TOO

WEAK

• JAM NUT

• TOO WEAK

• ( BREAKS AWAY

TOO SOON

AND DOES NOT

EXPAND SHELL )

WHAT IS THE RELATIONSHIP

BETWEEN THE WASHER AND

THE TENSION IN THE BOLT ?

• THE “K” FACTOR IS THE RELATIONSHIP

BETWEEN THE WASHER & TENSION IN

BOLT

• NO WASHER K = 40

• HARDENED WASHER K = 50

• ANTIFRICTION WASHER K = 75 > 125» HARD PLASTIC

K FACTOR cont.

• TENSION IN BOLT = K x TORQUE

• FOR A BOLT USING A HARDEN

WASHER AND HAS A TORQUE OF

150 FT- LBS

• TENSION IN BOLT = 50 x 150

• TENSION IN BOLT = 7500 LBS

MECHANISMS OF MECHANICAL BOLTS

MODERATE

CLAMP

LOADS

MODERATE PLATE LOADS

MODERATE TO HIGH

ANCHORAGE

DEPENDING ON THE

STRATA

CLAMP LOADS DEVELOP

SOME SHEAR RESISTANCE

ALONG BEDDING PLANES,

SLIPS AND JOINTS

MECHANISMS OF FULLY GROUTED BOLTS

LOW PLATE LOADS

HIGH ANCHORAGE

DEVELOPED ALONG

BOLT LENGTH

NO CLAMP

LOADS

LITTLE OR NO SHEAR

RESISTANCE ALONG

SLIPS AND JOINTS

UNLESS INTERSECTED

BY BOLT

HIGH SHEAR RESITANCE

ALONG RESIN/ROCK

INTERFACE

RESIN ANCHOR

TORQUE TENSION BOLT

• IN THE FIRST

TYPE OF

INSTALLATION,

TWO FOOT OF

FAST SETTING

RESIN IS USED,

AND THE REST

OF THE HOLE IS

LEFT OPEN

RESIN ANCHOR

TORQUE TENSION BOLT

• SECOND TYPE, ONE

TO TWO FOOT OF

FAST SETTING

RESIN IS PUT IN

THE BACK OF THE

HOLE, WHILE SLOW

SETTING RESIN IS

PUT IN THE

BOTTOM OF THE

HOLE

Aluminum Plug

Cast Dome

Shear Pin Tension Nut

Threaded

Deformed

Bar

TENSION NUTS

MECHANISMS OF TENSIONED REBAR BOLTS

VERY HIGH PLATE LOADS

EXTREMELY HIGH

ANCHORAGE REGARD-

LESS OF STRATA

VERY HIGH

CLAMP LOADSCLAMP LOAD DEVELOPS

VERY HIGH SHEAR

RESISTANCE ALONG

SLIPS AND JOINTS

HIGH SHEAR RESISTANCE

ALONG RESIN/ROCK

INTERFACE

Compression Tube

Deformed Bar

Mechanical Bolt

RESIN POINT ANCHOR WITH REBAR SUPPLEMENT

RESIN POINT ANCHOR WITH STEEL PIPE SUPPLEMENT

RESIN POINT ANCHOR WITH

SHEAR PIN & COMPRESSION RING

HIGH

CLAMP

LOADS

MECHANISMS OF POINT RESIN ANCHORED BOLTS

HIGH PLATE LOADS

HIGH ANCHORAGE

EVEN IN SOFT ROCK

CLAMP LOADS

DEVELOP

MODERATE SHEAR

RESISTANCE ALONG

BEDDING

PLANES,SLIPS AND

JOINTS

Grout

Column

Threaded

Deformed

Bar

Tensioning

CouplerShear

Pin

Bearing Plate

WHAT IS A SHEAR PIN ?

MECHANISMS OF COMBINATION BOLTS

VERY HIGH

CLAMP LOADS

VERY HIGH PLATE LOADS

EXTREMELY HIGH

ANCHORAGE

REGARDLESS

OF STRATA

GROUTED LENGTH

REINFORCES THE STRATA

LIKE A FULLY GROUTED BOLT

CLAMP LOADS DEVELOPS

HIGH SHEAR RESISTANCE

ALONG BEDDING PLANES,

SLIPS AND JOINTS

Support Characteristics

Fully

Grouted

Mechanical

Combination

Point

Anchor

Tensioned

Rebar

Very

High

Moderate

Very

High

High

Very

High

Low

Moderate

Very

High

High

Very

High

High

Low

Medium/

High

Low/

Medium

Very

High

Medium/

High

Low

High

Medium

Very

High

Anchorage ClampingVertical

Stiffness

Horizontal

Stiffness

Frictional

AnchorsLow Low Low Low

Bolt Type

Full Contact Supports

Anchorage Length

* Resin Anchored

* Friction Anchored

(Split Sets, Swellex, Friction Loc)

Friction Anchor Resin Anchor10 Tons+ Per Foot1 Ton Per Foot

Anchorage

Constant

Along The Bolt

Length

Anchorage Variable

Along Bolt Length

FULL CONTACT

SUPPORTPOINT ANCHORED

SUPPORT

FRICTION ANCHORED

SUPPORT

(SPLIT SET)

POINT ANCHORED

SUPPORT

(MECHANICAL BOLT)

10’

Anchorage

1 Ton/Ft.

(10 Tons)

Anchorage

10 Tons

FRICTION ANCHORED

SUPPORTPOINT ANCHORED

SUPPORT

10’

Anchorage

1 Ton/Ft

(8 Tons)

Anchorage

10 Tons8’

FRICTION ANCHORED

SUPPORT

POINT ANCHORED

SUPPORT

10’

Anchorage

1 Ton/Ft

(1 Ton)

Anchorage

10 Tons

1’