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AMERICAN ENGINEERING TESTING, INC. AET Project No. 26-41538 <br /> 5.4 Review of Soil Properties <br /> Generally, the sails in the upper profile of the existing roadway are fill soils consisting of sands, <br /> sands with silt, and silty sands. These soils range from moderately fast to moderately slow <br /> draining and have a low to moderate susceptibility to frost heaving during freezing temperatures. <br /> However, the silty sand soils can hold water or impede infiltration of water, and can then trap <br /> water in the aggregate base and/or upper zone of the subgrade. When these soils are wet and <br /> subjected to vehicle traffic, subgrade instability, softening, weakening, and differential frost <br /> heaving can result. <br /> 6.0 RECOMMENDATIONS <br /> 6.1 Definitions <br /> Italicized words used in this section have a specific definition or a Mn/DOT reference. The <br /> definitions are presented on the attached standard sheet entitled "Definitions Relating to <br /> Pavement Construction"or are defined in an ASTM standard or a Mn/DOT specification. <br /> 6.2 Subgrade Preparation <br /> 6.2.1 Suhgrade Preparation <br /> As described above, all borings encountered layers of uncontrolled fill below to roadway. <br /> Ultimately, our recommendation is to remove any uncontrolled fill in an effort to reduce the <br /> likelihood of differential settlements of the pavements. However,based on the past performance <br /> of the in-place material and because complete correction of the uncontrolled fill may be deemed <br /> non-cost effective. We are presenting a more cost effective option for the City in the <br /> recommendations below, however with this option there is some risk of long term differential <br /> settlement due to the presence of uncontrolled fill below the bituminous roadways. <br /> We understand that currently there is no plant to-incorporate the use of a sand subbase. However, <br /> in order to promote material uniformity provide consistent drainage below the pavements and <br /> aggregate base layer, we recommend that a 12-inch thick sand subbase layer consisting of Select <br /> Granular Borrow be placed as the upper zone of the subgrade. <br /> Page 4 of 9 <br />