Entry Into An Abandoned Underground Mine

George H. Davis, R.G., C.P.G.Adjunct Faculty, Missouri State

UniversityAnd Senior Geotechnical Specialist,

Missouri Department of Transportation

Prepared for the Interstate Technical Group on Abandoned Underground Mines (ITGAUM) Biennial Meeting 2006 – Rochester, N.Y.

Why would you EVER want to enter an abandoned mine?

• The mine is designed safely for underground storage, business, or other commercial purposes.

• To aid someone trapped inside the mine, and hopefully save them from injury or death.

• To protect the public IF and ONLY IF the risk presented is minimal to YOU, when there is NO OTHER WAY TO DETERMINE THE INFORMATION NEEDED TO PROTECT THE PUBLIC!

Missouri’s Underground Mines• Lead/Zinc mining

– Tri-State District– Viburnum Trend– Bonneterre District

• *Limestone mining *• Coal mining – now all

abandoned• Iron ore +REE deposits• Silica mining –

– US Silica near Pacific– Crystal City (abandoned)

Missouri has more underground space resources than any other state in the US

• Branson• Columbia• KANSAS CITY• Springfield

ALL ARE DESIGNED FOR FUTURE USE!

But, what about other mines that are abandoned?

Are any of them suitable for underground storage space, or do they

represent public hazards?

Fred Weber, Inc.O’ Fallon Quarry

• Near O’ Fallon, Missouri, St. Charles County

• An allegation by a private citizen pointed to the possibility of the horizontal adits near the top of the quarry wall going under I-70.

These shafts have been abandoned for more than 25

years!• No mine maps or records

to indicate where and in what direction the aditsgo.

• No reliable anecdotal evidence from Fred Weber, Inc., as the quarry ownership changed after mining ceased.

At risk – Interstate 70

• Does the mine go underneath I-70?

• If so, how far?• If not, how close does it

come to the edge of the right-of-way?

DOES THE ROAD NEED IMMEDIATE CLOSURE?

Safety Preparations for Entry

• What will we encounter?– Hazardous wastes?– “Critters”?– Gases?– Will any of these behazardous to the team?

• What physical mine conditions of danger are there?– Roof collapse and

potential for more– Rib (wall) instability– Pillar instability

Gas Hazards – Potential

• Toxic Gases – SO2 and SO3, being heavier than air, may concentrate in low areas –These gases are DEADLY!

• Asphyxiants – CO – Buildup of carbon monoxide in closed spaces is also deadly.

• Explosive gases – methane, fuel vapors These all need to be monitored continuously

with low threshhold detection limits.

“Critters”

• By this, we mean animals that can either be a simple nuisance (like a skunk), or harmful to you (rabid bats, rodents)

This item is best handled by a simple policy of AVOIDANCE – leave ‘em alone and they shouldn’t bother you.

Hazardous Waste?

• A wide variety of unreported hazardous waste may be inside a mine that could be more than a team can handle.

• One rule only in this case: EXIT!

Interior Mine Physical Conditions

• Roof Collapse and Potential for Future Collapse

• Rib (wall) instability

• Pillar instability

Equipment needs

• Gas detection– 3-phase gas detector,

detected LEL (lower explosive limit) of flammable gases but set at TLV (threshold limit value) of detection

– Also TLVs of SO2, SO3, CO

• Light – 3 sources per team member –– 2 electrical with extra

batteries – flashlight, headlamp

– Cyalume sticks

• Standard PPE (Personal Protective Equipment)

Entry into the mine

• Entry was made into the cavity on this hillside, immedatelyabove a 100’ vertical drop into the old Weber O’Fallon pit.

Each individual cavity was photographed, videotaped and

measured.• Abundant roof spall

made footing treacherous.

• Sides of pillars also spalling – will eventually lead to general cavity collapse

What did we find?

• Measurement of the mine cavity from front to back was approximately 225’

• The total mine length was about 2000’ long, and paralleled I-70.

• Three sets of pillars were spaced approximately 35-40 feet apart in irregular staggered rows, which made it impossible to see the corners of the cavity from any one point.

Condition of the mine

• The interior of the mine was climbing upwards, similar to the interior of a cave that was “doming out” to a sinkhole.

• Roof instability –many hanging slabs, which we avoided.

• Pillar and rib instability – the rule we followed said NO ONE was to touch anything but the floor.

• Rubble piles only 100 to 150 feet inside the mine, then the original floor.

Our “Hazards” Checklist

• “Critters” – the only animals found inside the mine cavities turned out to be pigeons, though bat guano was found.

• Gases – both the HNU unit and multigasdetectors carried detected no harmful gases.

• No hazardous waste or other harmful items (including explosives) stored inside.

What did we learn?

• Most importantly, the mine cavity stopped 75 feet short of Interstate 70 right-of-way, at an estimated elevation of 40 feet above the top of the cavity.

• The entry offered a unique opportunity to view a karst-like “climbing cavity”

• Two different mechanisms probably responsible for roof collapse – frost and blast vibrations from the nearby Weber-O’Fallon open pit operation.

Team Members – Composition

• One geologist, two assistant fire chiefs from the City of Wentzville and the City of O’Fallon, two fire captains…….

Would we do it again?

YES, if the public were at risk!