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'. '" - -. '' Brighton Water Storage Project Slope Stability Calcalations Adams Couoty, Colorado Prior to filling, the top 12 inches of in-place materials on which fill soils will be placed should be scarified, moisture conditioned and properly compacted to provide a uniform base for. fill placement. Soils that classify as A-1 through A-5 (granulaz materials) should be compacted to 95 or more percent of the maximum modified Proctor dry density at moisture contents within 2 percent of optimum moisture content as determined by ASTM D-1557. Soils that classify as A-6 and A-7 (cohesive soils) should,be compacted to 95 percent of the maximum standard Proctor density at moisture contents from 1 percent below to 3 percent above the optimum as determined by ASTM D-698. If surfaces to receive fill expose loose, wet, soft or otherwise deleterious material, additional material should be excavated, or other measures taken, to establish a firm platform for filling. , Fill materials should be thoroughly mixed to achieve a uniform moisture content, placed ins uniform lifts not exceeding 8 inches in loose thickness, and properly compacted. Soils that classify as A=1 through A-5 should then be-compacted to 95 or more percent of the maximum modified Proctor dry density at moisture contents within 2 percent of optimum moisture content as determined by ASTM D-1557. Soils that classify as A-6 and A-7 should be compacted to at ,least 95 percent of the maximum standard Proctor density at moisture contents from 1 percent below to 3 percent above the optimum as determined by ASTM D-698. - The Gebtechnical Erigineer should observe the exposed excavation surface prionto placement of fill, and observe earthwork operations and test the soils. Excavation Considerations Test holes for subsurface exploration were advanced to the depths indicated on the test hole logs by means ofbuck-mounted, flight auger equipment. We anticipate no unusual .excavation difficulties-for the proposed embankment in these materials with conventional, heavy,-duty excavating equipment in good working condition. , Groundwater was encountered during subsurface exploration at depths of about 18 to 27 feet below existing grades at top-of-slope. The -shallow groundwater conditions are interpreted to indicate that the water was perched in the sands and gravels; on the relatively low permeability bedrock. The sands and gravels are relatively permeable and should drain comparatively rapidly. Likewise, local groundwater will tend to flow toward the site relatively rapidly aftar-site water levels are lowered. The Contractor should take care to ensure a drained condition during project excavations and pond wall construction. Active dewatering systems may be prudent. Seepage will significantly reduce factors of safety below those values discussed above for the temporary slope geometries. Job No. 02-0065 Ground Engineering Consul[an[s, Inc. Page 4