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REFUSE PILE EXPANSION
<br />laboratory soil testing, and previous triaxial thickness of 2 feet. HDPE was assigned a cohesion
<br />shear tests taken at various sites within the (tensile strength) of 1000 psf, internal friction angle
<br />WEM (see Table 5 Summary of Strength of ] 8 degrees, and weight of 2 pcf. PVC was given
<br />Parameter Data for RPE Slope Stability a tensile strength of 1000 psf, internal friction angle
<br />Analysis). They are as follows: of 25 degrees, and weight of 2 pcf.
<br />- Alluvial Gravel: Non-cemented
<br />gravel, cohesion 250.0 psf, intemal
<br />fiction angle 29.0 degrees, moist unit
<br />weight 110.0 pcf, saturated unit
<br />weight 115.0 pcf.
<br />The input information for the analyses includes
<br />slope geometry, groundwater conditions, soil
<br />strengths, and loading conditions (See Appendix K
<br />for slope stability calculations).
<br />5.5.3 Analyses Results
<br />- Colluvial Soil: Low plastic clay,
<br />cohesion 193.00 psf, internal friction
<br />angle 21.6 degrees, moist unit weight
<br />100.0 pcf, saturated unit weight
<br />118.0 pcf.
<br />- Bedrock: Mesa Verde Sandstone
<br />group, cohesion 200,000.0 psf,
<br />intemal friction angle 40.0 degrees,
<br />moist unit weight 150.0 pcf, saturated
<br />unit weight 150.0 pcf.
<br />- Bedrock: Coal, cohesion 400.0 psf,
<br />~~ intemal friction angle 21.0 degrees,
<br />moist unit weight 90.0 pcf, saturated
<br />unit weight 80.0 pcf.
<br />- Bedrock: Shale, cohesion 600.0 psf,
<br />internal friction angle 25.0 degrees,
<br />moist unit weight 115.0 pcf, saturated
<br />unit weight 130.0 pcf.
<br />- Coal Refuse: Coal ,cohesion 800.0
<br />psf, intemal friction angle 39.0
<br />degrees, moist unit weight 58.0 pcf,
<br />saturated unit weight 68.0 pcf.
<br />- Engineering Fill: Local borrow source
<br />clays (low plastic), cohesion 2000.0
<br />psf, internal friction angle 0.0
<br />degrees, moist unit weight 100.0 pcf,
<br />saturated unit weight 1 18.0 pcf.
<br />In addition, three liner materials, compacted clay,
<br />HDPE, and PVC, were incorporated into the
<br />investigation of [he RPE. Compacted clay was
<br />assigned a cohesion of 2000 psf, internal friction
<br />angle of 0 degrees, a weight of 125 pcf, and
<br />5.5.3.1 Internal Stability of RPE
<br />The slope stability analyses involved evaluating all
<br />phases of RPE development including original terrain
<br />slope conditions prior to RPE construction. The
<br />stability of the RPE during an earthquake event was
<br />also investigated using an assumed maximum
<br />horizontal and vertical ground acceleration of 0.1 g
<br />(earthquake loading factors). Original terrain slope
<br />conditions were evaluated to understand current slope
<br />failure mechanisms, and how the advancing proposed
<br />RPE will impact the natural slope. The study
<br />indicated construction of the RPE generally improves
<br />the stability of the slope on which the repository is
<br />proposed. Critical failure circles and their associated
<br />factors of safety can be found in Appendix K. The
<br />complete results of the slope stability local analysis of
<br />the RPE can be found in Table 6.
<br />The stability analysis indicates that the native slope
<br />has a minimum factor of safety of 1.50 for static
<br />conditions and 1.19 for psuedostatic conditions along
<br />Profile 3. Construction of the RPE improves the
<br />factor of safety to 1.83 for static conditions and 1.47
<br />for psuedostatic conditions along Profile 3 at the end
<br />of the Phase 4 buildout.
<br />The critical period during construction, when factor
<br />of safety results are lowest, will be during [he Phase 1
<br />cut. To mitigate the area of cut exposure, a
<br />sequencing of construction stages for Phase 1 was
<br />developed, which results in four sub-phases- I A, I B,
<br />1C and ID. A stability analysis was performed for
<br />each sub-phase along each profile under static and
<br />psuedostatic conditions. The minimum static
<br />condition factor of safety is 1.55 during Sub-phase
<br />ID along Profile I. The minimum psuedostatic
<br />Harding Lawson Associates 10
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