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Report of Geotechnical Exploration and Review Fox Street Improvements, Orono, Minnesota AMERICAN July 29, 2016 ENGINEERING Report No. 20-14448 TESTING, INC. Page 8 of 12 Stability of the soils which remain within the critical subgrade zone should then be evaluated using the test roll procedure. It is expected that many of the in-place soils will be stable soils, such that significant stability improvement should not be anticipated. Any soft or yielding areas should be subcut and replaced with drier soils which are similar in type (for frost considerations). Where unstable soils are found under the test roll process, the soils should be improved by means of scarification, drying, and re-compaction; or by subcutting and replacement. We recommend the final soils remaining in place be capable of passing a test roll prior to placing the sand subbase or aggregate base. With this, it is our judgment that a test roll should not be necessary on the sand subbase layer, if incorporated into the design. A method of providing more uniform pavement support would be to subcut 1 foot, compact the bottom of the subcut with three passes of a vibratory roller, and then blend the excavated materials and replace and compact in 6 inch lifts. This process, commonly referred to as a compaction subcut, will provide a more uniform material for support and frost heave characteristics. 6.3.3 Geosynthetic Use A geogrid can be used as reinforcement to aid in off-setting subgrade instability. For stability improvement, the geogrid is ideally placed within an aggregate base layer, which better uses the tensile properties of the grid. However, you should recognize that the use of a geogrid over unstable soils may not necessarily provide an equivalent off-set (compared to proper soil stabilization). The geogrid manufacturer’s design engineers should be consulted to determine the proper product, aggregate base thickness, and product placement for use. A Type V geotextile fabric can be used for separation purposes, although the need for separation is not judged necessary when the existing subgrade is stable beneath the sand subbase (if incorporated). The placement of a Type V geotextile fabric would be beneficial if a sand subbase is not used and is placed below the aggregate base. 6.3.4 Fill Placement/Compaction Following the subcut excavation and stabilization of existing soils as needed, fill can be placed as needed to re-attain subgrade elevation. Fill should be placed per the requirements of MnDOT Specification 2105.3F1 (Specified Density Method). In ASTM terms, this specification requires