Roof Bolting AKM
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Transcript of 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’