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Report of Geotechnical Exploration and Review <br />Fox Street Improvements, Orono, Minnesota AMERICAN <br />July 29, 2016 ENGINEERING <br />Report No. 20-14448 TESTING, INC. <br /> <br /> <br /> <br />Page 6 of 12 <br />We recommend performing additional borings at a closer spacing (100 feet between borings or <br />closer) to better define the areas of organic soils below the roadway embankment. The borings <br />should be extended completely through the organic soils to the underlying mineral soils to <br />provide information for estimating future settlement in these areas based on the thickness of <br />organic soils and the embankment loading. <br /> <br />Lightweight fill is often used to reduce embankment loading. The unit weight of lightweight <br />materials is much less than soil, and substituting these materials for soil results in a lower unit <br />embankment load can result in less long term consolidation settlement of organic soils. <br />Common lightweight fill materials include shredded tires, Geofoam, and lightweight <br />manufactured aggregate. Geofoam is a manufactured expanded polystyrene that is strong, but <br />has a density of only about 1-3% that of natural soil. The additional geotechnical exploration <br />recommended above would allow a geotechnical engineer to evaluate the effects of replacing a <br />portion of the fill embankment with lightweight fill would have on long-term embankment <br />settlement. <br /> <br />Details of our recommendations for roadway reconstruction are found below. <br /> <br />6.2 Definitions <br />Italicized words used in this report have a specific definition or are a MnDOT 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 MnDOT specification. <br /> <br />6.3 Subgrade Preparation <br />6.3.1 Frost/Drainage Improvement <br />Current practice is to incorporate a sand subbase layer of Modified Select Granular Borrow <br />beneath the aggregate base layer for bituminous pavement systems. The purpose is to provide <br />improved drainage for the aggregate base and upper zone of the subgrade which better controls <br />frost heaving and thaw weakening effects. The appropriate sand subbase thickness is usually a <br />function of the underlying soil’s frost and strength properties, and the traffic loadings. <br /> <br />The upper subgrade soils in the critical subgrade zone consist primarily of lean clay, sandy lean <br />clay, and clayey sand, which would not meet a Modified Select Granular Borrow or Select