PERMFILE46577

• Permit No: C1981022
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: PREDICTED D-SEAM LONGWALL IMPACT ON BEAR CREEK ‎(ABEL 1998)‎
• From: Old Exhibit 2.05-E2 Part 7
• Section_Exhibit Name: Exhibit 2.05-E8 Part 5
• Media Type: D
• Archive: No

~cr-c r eb tin ly~J4 ,ohn h flbel Jr FAX N0. 3032788163 p,py
"~" Cpam/near Groak Impact Pago Z September 21, 1998
• of =ock above the excavated seam were highly fraet•ared, broken-up
fissured, rotated and only incompletely zecompacted. In the teen
of "D" Seam longwalls, that would be approximately 36 feet above
the pre-mining "D~ Seam roof. Tho lisauriLation decreased, or died
out rapidly, until at about tour seam thieknesaea above the seam
root, in this case approximately 48 feet, only line-f:ssuri2ation
was evident. ~t about nine seam thicknesses above the seam roof,
in this case approximately 109 leer, the strata appeared and
behaved as though it had never been disturbed. In other words,
Beyond nine seam thicknesses above the extracted seam root the coal
measure strata behaved elastically during their deileatinn into the
space opened up during the complete extraction o! the seam. =his
practical field lnlormation ie of trwmwndaue Importance to anyone
contemplating a longwall caving operation under a gas bearing rider
~PRm, R StreRm enure ~, a wator bearing aquifer or a aurtaca body of
water.
Gray, et al 11977). collected data lrom 350 sinkholes that
breached the Around aartace above room and pillar mine workings in
.he Pittsburgh Seam in Pennaylvanla. Only one of theca recorded
ehimneyo penctratcd through 200 teat o! overburden. Tiqurs 1
presents the cumulative percent probability that a collapse chimney
will tench, the ground surface through a given overburden thickness.
Piqutt' and Byc~on (1977) yreaanted a geometric method Of
predicting the height o! roof collapse above coal mine workings.
The method is shown on Flqure 2. Their rectangular collapse height
refers to caving of root abcve longwall panels, i.e, mine openings
w1Lr~ Large plan dimenaiona in all directions. Their wedge collapse
refers to caving of the root above long and narrow mine openings,
i,e. entries and rooms. Their conical collapse refers to Caving of
the roof above mina roadway iriteresctions, S.e. rooms and
crosscuts. Gray, et al's chimney collapse heights over room and
pillar workinga would have been for wedge and conical collapse and
not for rectangular collapse.
The height of root Collapse le direct Lunction of the mining
height and an inverse function o! the percwnt lree swell of the
immediate roof rocks. The percent free swell !or various rocks is
~roeentvd in Table 1. Proo avail ie critical because there can bo
no consolidation pressure on the caved root rock until the expnn-
slon of the eollapaod root rock !ills the mining void. Piggott and
eyncn's method predicts the maximum rectangular root eollapea above
s longwall panel to prooeed no morn than throe times the mining
height for a stale too! (339 free swell), 36 leer in the case of
the maximum p;annod 12-foot mining height for the ~D° Seem panels.
The minimum predicted root collapse height would be 1-1/2 times the
mining height for a aandotona root (67• tree swell), 19 lest it the
entire immediate root were sandstone.
•