2012-08-03_PERMIT FILE - C1981012 ‎(4)‎

• Permit No: C1981012
• IBM Index Class Name: Permit File
• Doc Date: 8/3/2012
• Doc Name: Design Recommendations for the Proposed West Portal Development Waste Rock Disposal Area ‎(DWDA)‎
• Section_Exhibit Name: Exhibit 43
• Media Type: D
• Archive: No

April 16, 2012
Table 6. Stability Factors for Various Slope Conditions
Page 10
Case
Side Slope Configuration
Depth to Groundwater
Stability Factor
Maximum permanent slope (H:V)
(H:V)
(ft)
2.0(H):1.0(V)
1
2:1
Not present
1.2
2
2.5:1
Not present
1.5
3
3:1
Not present
1.7
4
2:1
3 ft above bedrock at embankment toe (elev. 7,613 ft)
1.2
5
2.5:1
3 ft above bedrock at embankment toe (elev. 7,613 ft)
1.4
6
3:1
3 ft above bedrock at embankment toe (elev. 7,613 ft)
1.7
Although groundwater was not encountered during the site investigation, elevated
groundwater conditions were evaluated to account for seasonal fluctuations. Each slope
configuration case was evaluated with a groundwater surface to be 3 ft above bedrock at the
embankment toe (elev. 7,613 ft). The presence of groundwater, as modeled to elevation 7,613 ft
has nominal impact on the overall stability of the three slope configurations considered.
6.0 RECOMMENDATIONS
Based on the material properties obtained from the geotechnical drilling and sampling
program of March 2012 and the subsequent computer -aided modeling and analysis, AAI
recommends that the proposed West Portal DWDA be constructed to the criteria in Table 7.
Table 7. DWDA Recommended Construction Criteria
Configuration
Maximum height
90 ft
Maximum permanent slope (H:V)
3.0(H):1.0(V)
Maximum temporary slope (H:V)
2.0(H):1.0(V)
Embankment bench
10 ft wide, mid -slope (approx. elev. 7,660 ft)
Placement
Maximum lift thickness
2.0 ft
Minimum compaction
90% standard proctor
Moisture content for compaction
+/— 2% of standard proctor optimum
Several factors including foundation preparation, surface and subsurface water drainage, and
coal waste rock placement, affect the stability and performance of the waste pile. The following
recommendations are provided to fulfill assumptions made in the stability analysis and are
necessary to ensure an adequate safety margin is maintained:
1. To provide an adequate foundation - bearing surface, the topsoil, loose fill, man -made
debris, organic material, and all other deleterious material must be removed prior to coal
mine waste placement. If soft or low strength soils are encountered, they should be
removed to a more competent and suitable depth.
Agapito Associates, Inc.