ground control issues and roof support practices in
TRANSCRIPT
9/23/2014
Ground Control Issues and Roof Support Practices in Illinois #6 Coal Seam
by Drs. John Stankus, Hanjie Chen, Xiaoting Li
• Main causes of ground control issues in the #6 coal seam of the Illinois Basin
• Effective roof control practices
• Questions
Outline
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Main Causes of Ground Control Issues
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1. Regional horizontal stress
2. Weak immediate roof of #6 Herrin seam (Energy gray and Anna black shale)
3. Anvil rock sandstone is close to the roof line, water may occur
4. Presence of Jamestown coal rider
Typical stratigraphic column
Regional Horizontal Stress Effect
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Regional horizontal stress distribution in USA
The effect of the major horizontal stress on an entry/crosscut stability is categorized as follows when the angle () between the major horizontal stress and the entry/crosscut orientation is:
• ≤ 30, highly favorable
• 30 ≤ 60, moderately favorable
• 60 ≤ 90, unfavorable
Generally, N75E is accepted orientation of major horizontal stress in Illinois Basin
Simulation of Horizontal Stress Effect on Roof Stability of Set-Up Entries and Bleeder
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Due to the regional horizontal stress effect and longwall mining activity, stress concentrations may affect the roof stability in set-up or bleeder entries.
Mine Map
Stress Concentration Effect
Roof Support Practices - Primary Roof Support
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A tensioned bolting system works much better than a non-tensioned system in terms of the beam building effect and roof stability
Coal
Pillar Coal
Pillar
Tensioned bolt systems: InStaL, Super-Twist torque/tension
Roof Support Practices - InStaL Bolt and “TT” Anti-Frcition Washer
• “TT” anti-friction washer increases the installed load and tension/torque ratio by 20%
• Improves the beaming effect and roof stability in the highly stressed and laminated roof
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InStaL Bolt
Underground Roof Condition w/InStaL Bolts & “TT” Anti-Friction Washer
“TT” Anti-Friction Washer
Roof Support Practices - Supplemental Roof Support
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In highly-laminated weak shale roof and horizontal stress condition, a tensioned cable (either Post-Tensioned or InStaL CC cable) works more efficiently than a non-tensioned cable
Coal
Pillar T3/T5 roof channel
3045° 3045°
Coal
Pillar
Roof Support Practices - Post Tensioned and InStaL CC Cable Bolts
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Post-Tensioned (PT) Cable Bolt
InStaL CC Cable Bolt
Tensioned with Cable Tensioning Unit (CTU)
Tensioned with Expansion Shell
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Fully-Grouted Cable Bolt (FGCB) can be injected with polyurethane (PUR) to fully encapsulate the cable bolt and drill hole.
• Long term corrosion protection
• Water stoppage
• Strata stabilization
• Available as non-tensioned or tensioned InStal cable
Roof Support Practices – FGCB Injectable Cable
How does the FGCB work?
• Modified drive head to allow injection of PUR.
• Stiffener tube serves as a grout tube.
• Addition of rubber packer to pressurize drill hole.
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Installation Diagram
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1. Point anchor FGCB
into J-LOK resin 2. Inject PUR into
drive head
Point Anchored
w/ J-LOK
PUR
Water or
Fractured
Strata
Roof Support Practices - Trusses
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JMS Truss System
BYTM #8 Thread Bar Truss System
Roof Support Practices - Roof/Rib Corner Control
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PH Roof/Rib Channel prevents roof cutter induced by horizontal stress, enhancing roof and rib stability
Installed underground PH roof/rib channel installation
Roof Support Practices – Surface Control
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Surface control: roof channel, pan, mat, wire mesh are critical in preventing weathering effect and maintaining the roof stability
Steel Wire Mesh Roof/rib Pan
Roof T-channel
Roof Mat
Gateroad Pillar Design and Evaluation
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Pillars on the tailgate side of a panel are subjected to larger loading than those on the headgate side. To satisfy the ventilation requirements in longwall gates, the middle entry needs be maintained during longwall mining.
Finite Element Analysis Model
Vertical Stress Distribution
Gob
Gob
1.0 – 1.5 times overburden depth Large loading area
Advance
direction of
face
Pillar
Tailgate Chain Pillars
Roof Support Practices - Standing Support - Pumpable J-CRIB and J-PAK I & II
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Pumpable J-CRIB
J-PAK I J-PAK II
Before Test After Test Before Test After Test
Roof Support Practices - J-SANDY and RIP Steel Props
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Yieldable J-SANDY Prop
Rapid Installation Prop (RIP)
Roof Support Practices - J-SANDY NIOSH Test Curves
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Standard J-Sand Test Curve J-SandY Test Curve
Roof Support Practices - J-SandY NIOSH Test Curves
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J-SandY Test Curve with Yield Disk and Piranha Plate
Ground Support for a Slope - Geological Analysis
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Slope Orientation and Drill Holes Computer Model
Ground Support for a Slope – Geological Analysis
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0
100
200
300
400
500
600
0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800
Distance from the portal, ft
Sh
ea
r s
tre
ss
(V
on
Mis
es
) d
istr
ibu
tio
n
alo
ng
th
e c
en
ter
lin
e o
f s
lop
e r
oo
f, p
si
Shear stress before excavation
Shear stress after excavation
Unconsolidated
MaterialSS/SHA
CL/SHA
SLT SHA/LM/
SLT/CoalSS SLT
/SHA
/Coal
LM
SHA/LM
/Coal
SHA/SS/
Coal/LM
SLT
/SHA
/LM
Slope
Bottom
SS SS SLT
Shear Stress Distribution Along Roof Center
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800
Distance from the portal, ftS
tra
ta w
ea
kn
es
s i
nd
ica
tio
n f
ac
tor
alo
ng
th
e c
en
ter
lin
e o
f s
lop
e r
oo
f
Unconsolidated
MaterialSS/SHA
CL/SHA
SLT SHA/LM/
SLT/CoalSS SLT
/SHA
/Coal
LM
SHA/LM
/Coal
SHA/SS/
Coal/LMSLT
/SHA
/LM
Slope
Bottom
SS SS SLT
Strata Weakness Indication Factor (SWIF) Distribution Along Roof Center (weak strata with a SWIF 2)
Ground Support for a Slope - Square Set Design
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Installed Underground
Safety Factor (SF) Distribution (SF 1)
Square set design follows the American Institute of Steel Construction (AISC) national standard, and is based on actual geological and mining conditions
Square Set Design for a Slope Switch-Back Area
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Slope Switch-Back Area
Components and Dimensions
Installed Underground
Questions & Comments
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Contact Info:
www.keystonemining.com
www.jennmar.com/affiliates/kms
(412) 963-9071
Thank You!