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• 87 percent of maximum sized boulders passing beyond the road where no <br />mitigation measures were simulated <br />• • No boulders exiting the 10-foot deep trench and 10-foot high berm. <br />• 10 percent of the boulders passing beyond the 10-foot high berm <br />• No boulders passing beyond the top of the 20-foot high berm. <br />Closer inspection of the raw simulation output, and the data contained on Figure 4-2 <br />indicates that the trench and berm combination is superior to the other options. Similar <br />conclusions can be reached from inspection of Figures A-1 through A-29 and review of <br />the CRSP output (attached as a separate binder). Additional work (see Appendix C) has <br />also shown that the 'V' bottomed trench constructed with a 1.5:1 (H:V) impact slope <br />provides slightly better performance than the flat-bottomed trench shown in Figure 4-2. <br />4.3 Design Alternatives <br />Use of a rubber tire faced, 10-foot high soil wall has been suggested as an alternative <br />to the trench-berm combination in Zone 2 by Mr John White of the Colorado Geological <br />Survey. This method has previously been evaluated for use in controlling rockfall <br />hazards on Interstate 70 and has been tested at CGS' Rifle, Colorado site. <br />The vertical barrier is appropriate for zones where there is limited area available for <br />construction and such a case exists for construction of mitigative measures above the <br />existing road in Zone 2. Vertical barrier designs were prepared for this zone but will not <br />be implemented as there is concern that rock blocks resulting from toppling failures <br />would not be contained by a typical 10-foot high barrier. <br /> <br />22 <br />