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

9/23/2014

Main Causes of Ground Control Issues

9/23/2014

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

9/23/2014

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

9/23/2014

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

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th

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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

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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

9/23/2014

Contact Info:

www.keystonemining.com

www.jennmar.com/affiliates/kms

(412) 963-9071

Thank You!