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Geotechnical Report 2020 PMP Street Improvements Arden Hills, Minnesota WSB Project No. 014297-000 Page 6 4.5 Pavement Areas After removing the existing pavement sections and backfilling the utilities, the final subgrade should have proper stability within three vertical feet of grading grade (grade which contacts the bottom of the aggregate base). This will generally be achieved in fill areas with proper compaction of embankment materials and in cut areas through proper subgrade preparation. The stability of the pavement subgrade should be evaluated using the test roll procedure (MnDOT 2111), except a fully loaded tandem axle dump truck or a full water truck should be utilized for the proof roll. If unstable soils are found under the test roll, these soils should be improved by means of scarification, moisture conditioning, and re-compaction, or by subcutting and replacement. If the on-site soils cannot be moisture conditioned and compacted as recommended, we recommend removing these unsuitable materials and re placing them with Select Grading Material (MnDOT 2105.1.A.6). We also recommend a proof-roll be performed again on the aggregate base just prior to placement of the bituminous pavement. Table 3 below presents the approximate pavement section thickness and subgrade soils that were encountered within the borings. Table 3: Existing Roadway Soil Boring Profiles Boring No. Bituminous Thickness (inches) Aggregate Base Thickness (inches) Subgrade Soils (Upper 4 feet) PB-1 4 7 Fill: Sand with silt PB-2 3 ½ 6 Fill: Silty sand and sand with silt PB-3 4 ½ 5 Sand and Sand with silt PB-4 4 ½ 7 Fill: Silty sand and sand with silt PB-5 4 7 Fill: Silty sand PB-6 4 3 Fill: Silty sand PB-7 5 4 Fill: Sand with silt PB-8 3 ½ 4 Fill: Lean clay PB-9 4 9 Fill: Sand with silt PB-10 3 7 Fill: Lean clay PB-11 3 ½ 7 Fill: Sand with silt PB-12 3 6 Fill: Sand with Silt PB-13 3 ½ 5 Fill: Sand with silt and silty sand Once the site has been prepared as recommended, we anticipate the subgrade will consist predominately sand with silt, sand and silty sand. The MnDOT Flexible Pavement Design Guidance Memo from January 2017, indicates soils such as those anticipated have an estimated R-value ranging from 20 to 70. It has been our experience that on projects with utility construction the final subgrades are generally a mix of soils excavated from the trenches. Also, lean clay was present in the subgrade at some locations, as such, we used an R-value of 20 for our design. Being traffic counts were not provided to us, we have assumed that the volume and distribution of vehicles using these roadways will have 20-year flexible Equivalent Single Axle Loads (ESAL’s) less than 75,000.