9.1. SR 01-07-2013 - Laserfiche WebLink

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AMERICAN ENGINEERING TESTING, INC. AET Project No. 26-00538 For more information about subgrade preparation and design, please read the standard sheet entitled"Bituminous Roadway Subgrade Preparation and Design" at the end of this report. 6. 2.2 Fill Placement and Compaction All fill should be placed and compacted per the requirements of M-n/DOT Specification 21053F I (Specified Density Method). This specification requires soils placed within the critical subgrade zone be compacted to a minimum of 100% of the standard maximum dry unit weight defined in ASTM: D698 (Standard Proctor test), at a water content 65% to 102% of the standard optimum water content A reduced minimum compaction level of 9510 of the standard maximum dry unite weight can be used below the critical subgrade zone. The sand subbase layer can be considered part of a composite subgrade; and the top of the subbase can be figured as the top of the 3 foot subgrade zone needing the 100% compaction level. Compaction of the fill should be performed with equipment that will provide the recommended compaction levels through the entire lift. 6.2.3 Subgrade Stability and Test Roll Subgrade stability within the critical subgrade zone is important for pavement support, construction and performance. With the 12-inch sand subbase layer comprising the upper foot of the critical subgrade zone, the existing soil portion (or new fill, if needed) will then comprise the lower 2-feet of the critical subgrade zone for the existing embankments. Stability of these existing subgrade soils should be evaluated, preferably using the test roll procedure, before placement of the sand subbase layer. 6.3 Estimated R-Value The limiting soils within the critical subgrade zone are the silty sands. These soils have an estimated R-value 'of 20. This estimate'is based on Table 5-13(a) within the 200 Mn/DOT Pavement Manual and our experience. Page 6 of 9