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2009-09-21_PERMIT FILE - C1981010 (13)
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2009-09-21_PERMIT FILE - C1981010 (13)
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Last modified
8/24/2016 3:55:39 PM
Creation date
12/1/2009 10:16:02 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981010
IBM Index Class Name
Permit File
Doc Date
9/21/2009
Doc Name
Trapper G-Pit Landslide Mining Assesment, January 2008
Section_Exhibit Name
Appendix T
Media Type
D
Archive
No
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January 15, 2008 <br />Page 33 <br />• Alternative 1-Remove the low strength Q-Floor material so that up to only 55 ft of spoil <br />rests on bedding with strength of at least 25° of friction. This can be accomplished by <br />using a dozer ripper to loosen the floor material down to more competent material. The <br />spoil material along the first 50 ft of the slope should also be compacted according to: <br />o Spoil lifts less than 1 ft thick compacted to about 6 inches <br />o Spoil water content increased for optimum compaction <br />• Alternative 2-Decrease the slope angle of the spoil pile to at least 1.7H:1 V and place up <br />to only 55 ft height of spoil as normal with the truck and shovel fleet. This alternative <br />reduces the volume of spoils that can be placed in such steep areas. <br />Both of these methods result in a reduction of the spoil pile height to 55 ft in steeper <br />bedding areas. It should be noted that no compaction tests have been performed to arrive at these <br />recommendations. Rather, general practice used at the mine has been applied. <br />The extent of the reduced-height spoil pile can be estimated from elevation contours of <br />the Q Floor mudstone (Figure 20). Using the Surfer program to compute the dip of the bedding, <br />contours of dip were developed as shown in Figure 21. The large red contour in this figure has a <br />dip between 14° and 16° covering 8.1 acres. This is the anticipated area were the lower 55 ft <br />height spoil pile is recommended. In other areas, the spoil pile height can be as high as 68 ft <br />without inducing potential stability problems. <br />The other significant parameter assumed in this analysis is the presence of groundwater. <br />These analyses have assumed that the majority of the spoil pile is drained and only 1 ft of head <br />exists on the weak Q-Floor mudstone. If the spoils are continuously drained, the foundation of <br />the spoil pile will be more stable. However, if the porosity of the spoils is less than expected, <br />then the phreatic surface in the spoils may be higher, in which case the foundation of the spoil <br />pile will be less stable. Groundwater in the spoils can be managed on the dipping beds by <br />engineering the base layer of the spoils to serve as a drain. That can be accomplished by using <br />only coarse spoils (i.e., <10% #100 fines) in the first 3 ft of the spoil pile. <br />Agapito Associates, Inc.
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