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

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45

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Roof/Rib

Other

0

5

10

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25

30

35

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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

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30

1 2 3 4 5 6 7 8 9 10 15 20 25 30

Years

0

5

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25

30

1 2 3 4 5 6 7 8 9 10 15 20 25 30

Years

Fre

qu

ency

Fre

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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)