2015-04-30_REVISION - C1996083 - Laserfiche WebLink

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Jason Musick -3- April 27, 2015 that the proposed post - mining final graded slopes are approximate in general to the pre- mining topography, please provide information discussing the grading plans associated with Borrow Area 1, 2, and 3 to incorporate into the proposed text of the PAP. Please also submit a figure or an addition to a figure that identifies the post- mining topography and cross sections of the post mining topography of the borrow areas. BRL: Slopes in the vicinity of borrow areas 1 -2 vary from 1.2H:1V to 4.5H:1V. The proposed final slope angles are 2H:1V. The natural angle of repose for most native materials in the area of gob pile #2 is 1.5H:1V. Please see a discussion about the borrow areas on page 8. New Figure 5 has been created detailing the locations of borrow areas 1 -2 and showing cross sections for each borrow area. 7. DRMS: In a report dated July 29, 2013, submitted with TR -81, BRL's geotechnical consultant analyzed the stability of a proposed expansion of Gob Pile #2. Results for Sections A -A' and F -F' were presented, showing that the minimum static Factor of Safety (FoS) of 1.5 could be achieved. With TR -98, a somewhat different configuration for the pile is being proposed, and although the peak elevation will not change, the thickness of material proposed for placement along the axis of the original valley is increasing (as shown on revised Section E -E' of Volume IX Figure 1). Material parameters utilized in 2013's TR -81 analysis differ slightly from those used in later analyses (for TR -84, MR -171, and TR -94) which were conducted by a different geotechnical consultant. Please analyze the stability of the proposed configuration depicted on Section A -A' of Volume IX Figure 1, to determine whether a minimum static safety factor of 1.5 can be achieved, in accordance with 4.10.4(2). If material properties used in this new analysis differ from those assumed in the recent revisions listed above, please provide a justification for the change, such as the coal mine waste's being blended with coverfill material to reduce the moisture content. BRL: Please see attached Huddleston -Berry Stability analyses dated July 30, 2014. 8. DRMS: During the Division's 2014 review of TR -89, the question was raised whether a stability analysis for ditch side slopes / borrow areas was needed, where cut slopes of 1.5h: iv were proposed. Rules 2.05.3(4)(a) and (d); 4.05.3(3) and (5); and 4.14.2(1), (1)(b) are pertinent to this situation. While 1.5h:1v slope is roughly equivalent to 330, which is typical angle of repose for many materials, the Division believes that a minimum static safety factor of 1.3 needs to be achieved for the cut slope proposed for Borrow Area #3. Please evaluate the stability of the proposed slope to ensure that the required FoS will be achieved.