COMPLIANCE INFO_FINAL WMU FU-23 DESIGN RPT & CONCURRENCE LTRS

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2. STABILITY ANALYSIS WMU FU-23. FORWARD LANDFILL PROBLEM: Assess the static stability of the refuse over the lining system for WMU FIJ-23 atthe Forward Landfill. Because WMU FU-23 is primarily an interior module with limited dimensions, the only slopes on this module that will coincide with the final landfill grades is the southern slope. However, final grades cannot be achieved without the construction of adjacent modules. Seismic analyses are, therefore, not required. GIVEN: These calculations have been previously performed lbr the prior WMUs at the site and they have been found to have a satisfactory factor of safety and seisrnic deformation. The analysis for WMU FU-23 is similarto WMUs FU-03, ART-03, FU-04, FU-05, FU-06, FU-08, FU-10, FU-13, FU-14, FU-17, FU-19 and various other WMUs at the site. SUMMARY: l,The planned maximum elevation of refuse in WMU FU-23, prior to the developrnent of adjacent waste management units, is I 10 ft MSL. This elevation is based on 3:1 slopes on the south, north, and east. The west slope will be filled against the existing WMU FU-17 and 19 refuse slopes. Development is planned to the east and nofth of WMU FU-23. The eastern and northern slopes are, therefore, temporary and will eventually be buttressed by adjacent slopes. STABILITY ANALYSIS SECTIONS AND CRITERIA: 1, The critical cross section for the stability analysis under the maximum interim filling configuration (refuse fill elevation 1 10 f0 is in the E-W direction along the base liner. 2. For interim slopes, a static factor ofsafety of 1.3 is typically considered acceptable. SUMMARY OF STABILITY ANALYSIS RESUI,TS 1. The minimum factor of safety for WMU FU-23 under the planned interim fill configuration (refuse elev. I l0 ft) is 1,78. The critical failure surface extends from approximately the crest of refuse, through the refuse mass, and then along a portion of the base liner, daylighting at the toe of slope. Both the base liner interfaces (claylHDPE and cushion geotextile/HDPE) were analyzed but the cushion geotextile/HDPE condition was found to be more critical. 2. The stability analysis assumes the base liner interface shear strengths between the clay and textured HDPE are a friction angle of I 8 degrees and an apparent cohesion of 0 psf and a fiiction angle of I 0 degrees and an apparent cohesion of 1,000 psffor normal load ranges from 0 to 6,500 psfand from 6,500 to 17,000 psf, respectively. The base liner interface strength between the cushion geotextile and the textured HDPE seomembrane is as follows: Normal Stress (psfl Minimum Shear Stress (nsf) 2.000 700 4,000 l.l l0 8,000 1.950 12,000 2.780 16,000 3,550 The interface shear strength envelopes for the critical surfaces are included with the calculations.