Roof and Ground Control Regs ©2004 Dr. B. C. Paul

Regulations are by Sector Hardrock and Coal are Separate Underground and Surface are Separate Underground 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 principle Provide 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 (b)) Exception – Equipment with integral roof bolters don’t have to bolt right over machine Can 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 ) 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 (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 (a)) District Manager can also require tighter controls (30 CFR (a) and 30 CFR ) 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 (b)) If you open a cross cut have to bolt it on 5 foot centers before can use the intersection (30 CFR (e))

More Control of Roof Falls Rock Mechanics Class taught you math of two simple models Bolt 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 (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 (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 (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 (f) vs 30 CFR (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 (f)(3)) Tension must be checked on first roof bolt when installed every 4 there-after (30 CFR (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 (f)(5)) Grouted Bolts have to take 150 ft-lbs without turning in hole (30 CFR (g))

Secure Anchoring Holes for roof bolts must be within 0.03 inches of size specified by manufacture (30 CFR (e)) Requires keeping bits fresh or even using special marked finishing bits Size of Plates on End of Roof Bolts is specified as 5 inches – 4 inches if with wood between plate and roof (30 CFR (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 )

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 )

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 )

What has to be in a Roof Control Plan? Basic Company information Name and address of company Name address and MSHA # for the mine Name 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 supported When ATRS will be used and how far they may advance ahead of permanent support When tunnel supports arches and trusses will be used Openings 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 )

Why are Roof Control Plans and Procedures a Big Deal Study Period Underground Coal Mine Fatalities through September 6, We are Killing 70% of our people with Roof and Rib Falls

Fatalities by Type of Mining Loosing most people in room and pillar operations in the face areas

Who are we killing off? Mostly Miner Operators, Bolters, and Foreman

Victim 50% of Roof Fall Fatalities

Intersections 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 OccurrencesOccurrences Note: These factors are not mutually exclusive.

Roof/Rib Fatalities (‘94-’99) Experience at Mine Frequency Median = 1 yr.

New 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 assumed Need be added only where conditions and experience shows it is warranted Program 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 )

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 and 30 CFR )

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 MSHA Director does not have to approve the plan Plan 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 ) 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 )