Week 9

©2012 Dr B C Paul

Coal

• Trouble in the Board Room– Plans to ignore large amounts of met coal and

drop mining your low sulfur coal and cut down on mine size and profits were not well received.

• To convince the Board that dropping the 5 seam is justified– Create contour maps of the thickness of the 6

and 5 seam innerburden

Contour Maps

• The Board agrees that you cannot mine within 30 feet of inner-burden– (you could cave between seams)

• The Board wants you know what percentage of your #5 coal is has less than 90 ft of inner-burden and where that coal is.– One of the reasons you can’t stack pillars is that soft clay floors

produce larger pillars than the Holland formula• But some parts of the #6 coal also have thick enough clay to take

control of pillar size

– Show what parts of the #6 coal have clay floor dominating their pillar sizes (produce an isopac map of the thickness of clay floor on the #6 seam.

The Board and Rock Mechanics Constraints

• 90 feet is the distance at which seam interaction begins to become apparent– Pillar stacking copes with seam interaction but it may not be the

inevitable choice.– For distances between between 70 and 90 feet assume that if

you synchronize the time of mining that most interaction will be negligible

• If you mine #6 first then for 80 to 90 feet your ground control costs on #5 will increase 5%

• For 70 to 80 feet the increase in ground control costs will be 10%

– For 60 to 70 ft assume that if you synchronize mining your ground control costs in #5 will go up 5% and will be up 20% if you do not synchronize.

– For closer than 60 feet assume you do have to line up pillars

Convince the Board

• If you want to convince the board to go for dropping the #5 seam– Show that a large enough part of the #5 coal is within 60 feet

and in an area where the #6 coal is pillar strength controlled rather than floor controlled

• Also show that there is no way to line pillars up by making long pillars in the #5 seam or make #5 pillars large enough to cover 2 #6 pillars (ie – no chance for creative geometries that don’t kill your recovery)

– You can also throw out the 60 to 90 foot distance coal if you can show that the increase ground control costs are economically prohibitive to mining and that there is no way for you to synchronize the time to mine the two seams at the same time

• If you can’t do it – the Board says you need to work a plan to mine #5

Your #2 and #5 Coal

• The board wants to know the cost per foot if you punch through a stream channel– If you have to use a grout curtain– If you don’t have to use a grout curtain

• The board wants you to use your geologic judgement and knowledge of mine timing to pick two places for each seam where you might be able to punch through the channel– The board will fund you 7 holes across each corridor to verify the

width of the channel to be cut through– The board will also fund pump tests on those holes to get an

estimate of just how much water you could face in going through• The board also wants to know the cost of ramping down

from the #6 coal into #5 and #2 on the other side of a sandstone channel

Your Testy Board

• You proposed not mining a portion of the #6 coal that had thin unstable shale roof– Your #6 timing assumed your pillar size was universally

governed by Holland and pillar strength– The Board believes you may have some clay floor areas that will

cut your recovery in #6. You may need some of that shale roof coal to make up the difference

• The Board wants to know why you chose not to cut-down the thin shale roof and then remove it from the coal in the preparation plant– Arguments that make money sense always please the board– They will also listen to safety and technical arguments if you can

make them persuasively.

What to Do This Week

• Provide the isopac maps required by the board

• Provide a map showing where you believe the stream channel is in the #2 and #5 coal– By Monday show where you want to drill the

holes to check your crossing corridors.

• Put together the timing maps for all coal seams that you will mine.

More Work

• Put together an outline of how you think your final report can be organized.