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<br />6 <br /> <br />4.3 Roadways & Utilities <br /> <br />Excavations The existing gravel surfacing (aggregate base), especially at boring SB-3, has <br />likely been compromised over time and will likely not be reusable as “new” aggregate base <br />and should not be relied upon or substituted for “new” aggregate base. We therefore <br />recommend that the existing gravel surfacing be moved to accommodate the new gravel <br />section. As noted above the aggregate base at SB-1 might be suitable for reuse but should be <br />tested to confirm that it meets MN/DOT requirements. <br /> <br />Where the roadway is widened, we recommend that all vegetation and topsoil and any other <br />soft or otherwise unsuitable materials, be removed from below the roadway and oversize <br />areas. Table 2 summarizes the anticipated excavation depths at the boring locations. Since <br />the borings were spaced fairly far apart excavation depths could vary and could be deeper. <br /> <br />Table 2. Anticipated Soil Excavation Depths <br />Boring <br />Number <br />Estimated <br />Surface <br />Elevation (feet) <br />Anticipated <br />Excavation <br />Depths (feet)* <br />Anticipated <br />Excavation <br />Elevation (feet)* <br />Anticipated <br />Groundwater <br />Elevation (feet)* <br />SB-1 985.9 ½ 985 ½ NE <br />SB-2 982.8 2 (Pond) 981 (Cut to grade) NE <br />SB-3 997.0 2 995 NE <br />* = Excavation depths and elevation were rounded to the nearest ½ foot. <br /> <br />Oversizing In areas where the excavations extend below the proposed pavement or utility <br />elevations, the excavation requires oversizing. We recommend the perimeter of the excavation <br />be extended a foot outside the proposed footprint for every foot below finish grade (1H:1V <br />oversizing). The purpose of the oversizing is to provide lateral support of the pavement or <br />utility. <br /> <br />Selecting Replacement Backfill Additional fill will likely be required for embankment <br />construction and to replace any topsoil or any soft or otherwise unsuitable materials. <br /> <br />Where the excavations bottoms are wet or submerged, if any, we recommend initially <br />backfilling to a height no less than 2 feet above the excavation bottom or water surface with <br />imported coarse sand having less than 50 percent of its particles by weight passing the #40 <br />sieve and less than 5 percent of its particles passing a #200 sieve, such as MN/DOT 3149.2B2. <br />Alternately “clear rock” (coarse filter aggregate) can be used in wet excavations. <br /> <br />Fill and backfill above the water table can consist of any debris free, non-organic mineral soil. <br /> <br />Topsoil, organic soils or soils that are black in color are not suitable for use or reuse as <br />structural fill or backfill. <br /> <br />Backfilling & Compaction We assume that new pavements will be constructed over the top <br />of the utility trench(s) and that soil excavated for pipe installation will be placed back in the <br />excavations, to the greatest extent possible. It is our opinion that the on-site soil encountered <br />in the borings is generally suitable for re-use as fill and backfill provided it is free of topsoil, <br />organic soils or other unsuitable materials. We do not recommend re-using topsoil, buried <br />212