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2014-02-10_REVISION - C1996083 (2)
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2014-02-10_REVISION - C1996083 (2)
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Last modified
8/24/2016 5:39:52 PM
Creation date
2/10/2014 12:30:08 PM
Metadata
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Template:
DRMS Permit Index
Permit No
C1996083
IBM Index Class Name
REVISION
Doc Date
2/10/2014
Doc Name
Adequacy Review Response
From
J.E. Stover & Associates, Inc.
To
DRMS
Type & Sequence
TR85
Email Name
SLB
SB1
Media Type
D
Archive
No
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Susan Burgmaier -2- February 3, 2014 <br />2008 study did consider a phreatic surface based on pore pressure measurements <br />and also conducted a sensitivity analysis using an increased phreatic surface. In <br />that study, block failure as well as circular failure was considered. <br />Buckhorn's Summary of Instrumentation Monitoring for the 3rd Quarter 2013 <br />includes data for a series of Vibrating Wire Piezometers (VWPs) that have been <br />installed in Gob Pile #2 and are read on a quarterly basis. VWP -06 and -08 are <br />located in the general vicinity of the proposed Drying Area, and continue to show <br />somewhat elevated pore pressures, in the range of 14 to 16 psi. These values <br />stand in sharp contrast to the 1 to 3 psi reported for VWP -05, -09 and -10 which are <br />installed near the toe of the pile. <br />a) Given the fact that pore pressures in the upper portion of Gob Pile #2 have <br />not yet diminished, please expandthe stabilityanalysis to address the <br />effects (if any) of the proposed Drying Area on the pile as a whole, <br />using the approved outs lope configuration and the current slope of <br />the compacted coal mine waste that will form the base of the <br />DryingArea. Based on previous Buckhorn studies, thismayrequire <br />consideration of phreatic surface and block -type failure surfaces <br />using total stress analyses and un- drained strength parameters <br />b) Currently, there are only two functioning VWPs in the upper levels of Gob <br />Pile #2: VWP -06 and -08. Please address any impacts to the Gob Pile <br />#2 VWPs thatmayoccurasa resultof constructing the DryiagArea, <br />e.g. will either installation be destroyed, or made inaccessible. If <br />any impacts are expected, please provide recommendations <br />regarding any proposed mitigation, such as installation of new <br />VWPs <br />B W2: Please see Buckhorn's response in attached document. <br />3. DRMS: Buckhorn's Model #11 a 15 -foot pile at 1.5h:ly, results in a Factor of Safety <br />(FoS) of essentially 1.0, which implies that slippage of material down the slope is <br />imminent at all times. While this slope configuration may be acceptable on the sides <br />of the Drying Area, the Division questions whether this is appropriate for the front <br />face of the pile, where a commitment has been made to maintain a 25 -foot buffer. <br />Continual sloughing from the face of the Drying Area pile may encroach on the <br />required 25 -foot buffer between the end dumped material and the face of the pile. <br />If BRL will be placing material at 1.5:1 slopes, the buffer zone will need to be <br />increased to ensure that a minimum of 25 feet will be maintained at all times. <br />Alternatively, the slope of the front face of the Drying Area could be flattened to <br />increase the FoS and reduce the potential for sloughing of material into the buffer <br />zone. Please revise the plan to eitherincrease the pile setback to account <br />forsloughing of material, or flatten the proposed outerface of the Drying <br />Area to achieve an improved FoS, <br />
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