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>, <br />Retaining Wall Design <br />RPEE Haul Road Switchback, Gunnison County <br />An additional slope stability analysis was performed for the backslope material above the <br />wall. Although the results of the analysis indicate an acceptable backslope factor of <br />safety, we recommend the Owner consider the placement of geogrid reinforcement to <br />minimize potential sloughing (see Figure 4), and improve slope face performance, of the <br />on -site backfill. <br />Additional Retaininq Wall Recommendations <br />We highly recommend a representative of GROUND observe the retaining wall <br />excavation prior to the placement of reinforced and retained import backfill. <br />Imported wall backfill should be compacted to at least 95 percent of the modified Proctor <br />maximum dry density (ASTM D1557) at moisture contents within 2 percent of the <br />optimum. The wall subgrade at least 12 inches below the wall base and backfill placed <br />within 3 feet below the wall should be compacted to at least 98 percent of the standard <br />Proctor maximum dry density (ASTM D698) at moisture contents from 2 percent below <br />to 1 percent over the optimum moisture content. <br />A properly constructed wall drain system should be included in the retaining wall. <br />Drainage systems in retaining walls are intended to collect and divert water infiltration or <br />natural seepage. The wall drain system is not intended to handle surface runoff or <br />concentrated water, which should be collected and diverted by properly designed and <br />constructed storm drainage features. The areas surrounding the retaining wall should <br />be carefully graded to provide positive surface drainage away from the walls. The wall <br />system and the surrounding areas must be kept dry at all times during and after the <br />construction to prevent water from infiltrating into the wall systems. In no case shall <br />surface runoff be allowed to enter the wall construction areas or water be allowed to <br />pond around the walls. Temporary and permanent slopes and other stripped areas shall <br />be adequately protected against erosion. Erosion along the wall and slopes will result in <br />sloughing and could lead to a wall failure. <br />Closure <br />The proposed retaining wall must be constructed in accordance with the guidelines <br />presented in the drawings as well as material manufacturers' guidelines, unless <br />otherwise noted on the design drawings. <br />Based on the provided information, necessary assumptions, results of the retaining wall <br />design calculations, and the nature of the proposed construction, the design drawings <br />including Wall General Notes (Figure 1), Wall Site Plan (Figure 2), Wall Elevation (Figure <br />3), Typical Wall Section (Figure 4), and Typical Wall Details (Figure 5) are included in <br />this submittal. The proposed retaining wall must be constructed in accordance with the <br />guidelines presented in Appendix C, as well as the manufacturer's guidelines, unless <br />otherwise directed by the Design Engineer or otherwise noted on the design drawings. <br />Job No. 13 -3605 GROUND Engineering Consultants, Inc. Page 3 of 4 <br />