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HazeltinelRoad Runners Rest IllBrinkmann-Woodward Gravel Pits Lining Project-Design Technical Memorandum Denver Water August 2003 • Empty reservoir: o Water level inside the pit at top ofgound surface. o Water level in the South Platte River at EI, 5013. o Water surface outside of the pit in areas not along the South Platte River at 8 feet below existing ground surface. 3.6 Analysis Methodology The methodology used to develop the horizontal alignment design for the soil-bentonite cutoff wall (wall) involved identifying the limits of the safe crest width needed to provide an adequate FOS against critical failure surfaces from intersecting the installed soil-bentonite cutoff wall. The procedure used is shown schematically on Figure 3.1. Each representative slope cross section was analyzed for a minimum FOS and the critical failure surface was obtained. This critical failure surface was used to identify the zone of the slope that would be potentially unstable. The alignment was developed by placing the soil-bentonite wall outside this zone of potential instability. Analysis of the interior slope provided the "interior offset." Similarly, analysis of the exterior slope provided the "exterior offset." The distance between the two offsets provided the "safe zone" in which the soil-bentonite cutoff wall could be installed. In some locations, such as between Stations 40+00 to 64+00, we concluded that there was not sufficient crest width to allow installation of the wall in a safe zone. In these areas, because the exterior slopes cannot be modified, stabilization fill will need to be placed along the interior side slopes. The use of stabilization fill is discussed in Section 3.7. 3.7 Results of Stability Analyses Results of the stability analyses are summarized in Table 3.3 and discussed in the following paragraphs. Summary computer output of the analyses are provided in Appendix A. GEI Consultants, Inc. 11 o~osoo?-o~.n ~~-~azr~„~r~~u~T~~