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Roof and Ground Control Regs
©2004 Dr. B. C. Paul
Regulations are by Sector
Hardrock and Coal are SeparateUnderground and Surface are SeparateUnderground Coal Regulations are far
more specific and rigid than the other standards
Basic Approach in Underground Coal
Prevent people from working under unsupported top as a basic principle
Limit opening widths as a basic principleProvide for local variations by requiring
site specific roof control plans approved by local MSHA directors in specific mining regions
Roof Bolts are the Standard Support Method
Installed on a 5 ft X 5 ft pattern (30 CFR 75.222 (b))Exception – Equipment with integral roof
bolters don’t have to bolt right over machineCan space up to 10 foot across but have to
install a 2 or 3 inch board 8 inches wide between the roof bolts (30 CFR 75.205)
Installed to within 5 ft of face or edge of opening
Exception if have two rows roof bolts across an opening have to limit to 16 feet (ie edges may be 5 ft 6 inches) (30 CFR 75.222 (c) (2))
Avoiding Blind Roof Bolting
For strong reliable roof the District Manager can approve different spacing “provided that effective control of the roof, face and ribs can be maintained”. (30 CFR 75.222 (a))
District Manager can also require tighter controls (30 CFR 75.222 (a) and 30 CFR 75.202) How might he know?
Any roof falls above the roof bolts or shutting things down for more few hours have to be reported and marked on mine maps
Of course accidents are reported
Roof Fall Mechanisms and Regulations
Rock layers of roof like to separate into thin beams that cannot be supported over the opening width
One Way is to limit opening width Regs limit width to 20 feet Have to add support posts if go wider and limit road
width to 16 feet Only up to 30 feet under any circumstance (30 CFR
75.222 (b)) If you open a cross cut have to bolt it on 5 foot
centers before can use the intersection (30 CFR 75.222 (e))
More Control of Roof Falls
Rock Mechanics Class taught you math of two simple modelsBolt strata together to so that individual
layers become one as a laminated beam that will stand over the opening
Bolts using this mechanism must be at least 30 inches long (30 CFR 75.204 (f)(1))
Would need to show that your beam will stand over the opening width given strength of strata
Bolts may simply pin the immediate roof up to stiff strong main roof strata
Need to anchor 12 inches into strata (30 CFR 75.204 (f)(1))
How Do You Know the Stuff for Bolting Design?
Regulations require test holes 12 inches beyond the length of your roof bolts (30 CFR 75.204 (f)(2)) Roof control plan says how frequently test hole is
put up but 1 every intersection is not uncommon
Interesting peculiarity is that test holes are indicated for mechanically anchored roof bolts but not mentioned for grouted bolts (30 CFR 75.204 (f) vs 30 CFR 75.204 (g))
Bolts must be securely anchored
Roof Control Plan must specify a tension that does not exceed strength of bolt or the anchor strata (30 CFR 75.204 (f)(3))
Tension must be checked on first roof bolt when installed every 4 there-after (30 CFR 75.204 (f)(4))
When ever a section is worked 1 of 10 bolts has to be rechecked from outby edge of last open cross-cut to the face If majority fail must take corrective action (30 CFR
75.204 (f)(5)) Grouted Bolts have to take 150 ft-lbs without
turning in hole (30 CFR 75.204 (g))
Secure Anchoring
Holes for roof bolts must be within 0.03 inches of size specified by manufacture (30 CFR 75.204 (e))Requires keeping bits fresh or even using
special marked finishing bitsSize of Plates on End of Roof Bolts is
specified as 5 inches – 4 inches if with wood between plate and roof (30 CFR 75.204 (c))
Conventional (Wood post and set) Support
Maintains requirement for 5 ft centers and supporting to 5ft of the face Removing supports to work requires equivalent
temporary support Roadways limited to 16 ft wide with full
overhead support and 14 ft wide where only posts are used
Regs spell out size of posts or jacks, footing contact area etc.
(30 CFR 75.206)
Required to Work Under Supported Top
Operators have to stand back of permanent support lines while running miners 40 ft extended cuts require remotes Otherwise limit to 20 ft advance
Cross Cuts must be started from supported roof area Have to support the cross cut before the
intersection can be used People installing support have to work from
back under either permanent or outby of the last line of temporary support
Have to clearly mark (usually red flags or tape) the end of the permanent support lines
Regular Inspection
Visual inspection of the roof is required prior to any work in an area
If visual passes then the roof is sounded by a worker standing under supported top Have to have bars on the equipment or within four
cross cuts
Only after inspection and sounding can crews advance to support roof
(30 CFR 75.211)
Every Mine Must Have a Roof Control Plan
Plans and revisions must be submitted to MSHA District Manager Approved or denied in writing
Representative of the Miners must see the plans
All effected people must be trained in its provisions
Plan can be used only after approval and training of individuals
(30 CFR 75.220)
What has to be in a Roof Control Plan?
Basic Company informationName and address of companyName address and MSHA # for the mineName of company individual in charge of
the plan (ie contact)Basic Geology of the Mine
Cross section of mine strata showing seam and partings, at least 10 ft of floor and roof strata up to main roof (ie solid stuff you will anchor to)
Maximum cover in area to be mined
More Plan Contents
Mining and Support Sequences Illustrate and describe how mining
sequences will advance and be supportedWhen ATRS will be used and how far they
may advance ahead of permanent supportWhen tunnel supports arches and trusses
will be usedOpenings Dimensions and support
patterns
More on Roof Control Plans
Types of Support Must list all support materials to be used Hole sizes and bolt dimensions Can apply to conduct tests of something new with
District Manager approval but only people to conduct tests can be exposed to the support
How the Mine will protect people in vulnerable areas Drift Openings When approaching outcrop within 150 ft.
(30 CFR 75.221)
Why are Roof Control Plans and Procedures a Big DealWhy are Roof Control Plans and Procedures a Big Deal
0
5
10
15
20
25
30
35
40
45
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Roof/Rib
Other
0
5
10
15
20
25
30
35
40
45
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Roof/Rib
Other
Study PeriodStudy Period
Underground Coal Mine Fatalities through September 6, 1999.Underground Coal Mine Fatalities through September 6, 1999.
We are Killing 70% of our people with Roof and Rib Falls
Fatalities by Type of MiningFatalities by Type of Mining
DevelopmentOutby
Longwall
Retreat
Anthracite
DevelopmentOutby
Longwall
Retreat
Anthracite
2626
1515
1212
44 44
Loosing most people in room and pillar operations in the face areas
Who are we killing off?Who are we killing off?
CM
Bolter
Foreman
Haulage Maint.LW
Other
20201313
88
77 4422
77
Mostly Miner Operators, Bolters, and Foreman
VictimVictim
50% of Roof50% of RoofFall FatalitiesFall Fatalities
IntersectionsIntersections
One-half of roof fall fatalities in intersections
Intersections are typically 10-20% of developed area
80% of these fatalities in wide intersections
Intersection roofs weaker due to lack of rib support
One-half of roof fall fatalities in intersections
Intersections are typically 10-20% of developed area
80% of these fatalities in wide intersections
Intersection roofs weaker due to lack of rib support
Contributory Fatality Factors
0 10 20 30 40 50
Boom Holes
Ribs
Inby Support
Intersections
New at Mine
OccurrencesOccurrencesOccurrencesOccurrencesNote: These factors are not mutually exclusive.Note: These factors are not mutually exclusive.
Roof/Rib Fatalities (‘94-’99)Experience at MineRoof/Rib Fatalities (‘94-’99)Experience at Mine
0
5
10
15
20
25
30
1 2 3 4 5 6 7 8 9 10 15 20 25 30
Years
0
5
10
15
20
25
30
1 2 3 4 5 6 7 8 9 10 15 20 25 30
Years
Fre
qu
ency
Fre
qu
ency
Median = 1 yr.Median = 1 yr.
New at MineNew at Mine
Increased workforce relocation rate
Mature, experienced work force
Roof/rib control complex
Knowledge of roof does not transfer
Site-specific, roof/rib training deficit
Increased workforce relocation rate
Mature, experienced work force
Roof/rib control complex
Knowledge of roof does not transfer
Site-specific, roof/rib training deficit
Underground Hardrock
Universal Roof Support is not assumedNeed be added only where conditions and
experience shows it is warrantedProgram Relies on Regular Inspections
and roof and rib scaling with some local support
Work Area Inspections
Mine Operator must designate someone “experienced” to test and examine
Must examine work areas before shift, after blasting or if ground conditions change or warrant
Travel ways must be examined once a week (also applies to banks and surface highwalls)
(30 CFR 57.3401)
Regular Scaling
Before working or traveling in a problem area have to either scale down or support the rib or roof hazard
People cannot work on equipment from between the equipment and a rib or highwall
Where roof bolts are used the installation must essentially conform to the same standards as in an underground coal mine (Compare 30 CFR 57.3203 and 30 CFR 75.204)
Surface Coal Operations
Similar to Surface and Underground Hardrock with a few coal like twists
Must have a ground control plan in writing on file with the District Manager of MSHADirector does not have to approve the planPlan is to be based on sound engineering to
insure stability of highwall, banks and pits
Surface Coal Operations Cont.
Like Hardrock there must be inspections regularly and things must be fixed before working in area or marked and barriered off if not going to be fixed immediately. Inspections after every rain, freeze or thaw before
men work in the area (30 CFR 77.1004)
Need to ensure stability Have to either peel back loose overburden or put
up berms or barriers to prevent from rolling in
Working Between Equipment and a Highwall or Bank
For Hardrock the language simply says you shall not do it.Obviously would not work for narrow strip
mine with a highwall on one side and a spoil pile on the other
Says that it shall only be done for repairs and then only with precautions and plans to make sure the miner does not become pinned or trapped. (30 CFR 77.1006)