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March 2, 2020 <br />Project 19-460 <br />Jackson Hills Residential Suite <br />Phases II- IV <br />Elk River, Minnesota <br />We assume the foundation walls will be backfilled with imported sand materials. We recommend <br />all interior wall backfill be compacted to at least 98% of standard proctor maximum density and all <br />exterior wall backfill be compacted to at least 95% of standard proctor maximum density. We <br />recommend below grade walls be designed using a coefficient of active pressure (KA) of 0.33, an <br />at -rest coefficient (Ko) of 0.50, and a passive coefficient (KP) of 3.0. We recommend below grade <br />walls be designed using the bulk unit weight of 115 pounds per cubic foot. <br />E. Pavement Recommendations <br />We assume the parking lot subgrade will consist of imported sand material used for the site soil <br />correction. The expected subgrade poorly graded sand (SP) soils are classified as A-1-b soils in <br />accordance with the American Association of State Highway Transportation Officials <br />(AASHTO) classification system. A-1-b soils are rated excellent material for use as parking lot <br />subgrade material. In no instance should organic soils be used as parking lot subgrade material. <br />Without benefit of a laboratory R-value determination and based on Mn/DOT guidelines, an R- <br />value of 70 can be assumed for these materials. <br />Based on an assumed R-value of 70, we recommend the following bituminous pavement section <br />for general car and light truck parking lots: <br />Thickness Course/Description G.E. <br />1.5" Mn/Dot 2360 SPWEB240 Bituminous 3.4" <br />2.0" Mn/Dot 2360 SPNWB230 Bituminous 4.5" <br />6.0" M/Dot 3138 Class 5 Aggregate Base 6.0" <br />9.5" TOTAL 13.9" <br />In using the assumed R-value for bituminous pavement design, it is essential that the subgrade be <br />constructed of uniform soils at a moisture content and density in accordance with Mn/Dot <br />specification 2105 and capable of passing a test roll in accordance with Mn/Dot specification <br />2111. The native, undisturbed soils may need preparation (drying and compacting) to pass a <br />proof roll. If the subgrade is not compacted, uniform and capable of passing a test roll, then we <br />recommend the subgrade be scarified and recompacted or subcut and replaced with geotextile <br />fabric and select granular material meeting Mn/Dot specification 3149. The top of the subgrade <br />Page 9 <br />