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Hennepin County AET Project No. OS-06764 May 24, 2016 Page 4 of 5 Frost heave is a cumulative process with the heaved anchor or tower base rods not returning to its pre-heaved state when thawing occurs. Consequently, the anchor or rod slowly gets jacked out of the ground each year frost heave occurs. Based on the length and embedment angle of the proposed helical anchors, about 3.9 feet of embedment is anticipated below the ground surface. Based on this, some frost heaving of the helical anchors and tower base rods may occur. If heaving does occur, it will tend to reduce the tension in the guy wires. We recommend that the tension in the guy wires be checked on a periodic basis to look for signs of frost movement. More substantial frost heave could occur with the concrete deadman anchors due to frost heaving below the base of the deadman anchor and additional heave due to frost adhesion of the buried portion of the deadman anchor. As previously indicated, up to 3 inches of heave could occur during a severe winter. We anticipate that the potential frost heave of the tower base, if it is placed on the existing soils, would be similar to the potential heave of the deadman anchors. Heaving of the tower base would increase tension in the guy wires and could potentially cause damage to the tower structure. Other Recommendations We recommend at least quarterly observation of the guy wires, anchoring devices and tower base in arder to detect possible movement due to frost action or settlement. If minor movement of the anchors or the tower base is noted, adjustments to the guy wire tension should be made. If cumulative frost heave movement is significant, the anchors should be reinstalled to their pre- heave depth. Preparation of the tower base subgrade should involve removal of any vegetation and any organic soil with over 3 percent organic content by weight from within the tower base area and a minimum 3-foot oversize area. Additional excavation should be completed as necessary to allow placement of a minimum of 6 inches of Class 2 aggregate base. Prior to placement of the aggregate base, the exposed subgrade should be surface-compacted with a minimum of four passes with a vibratory compactor having a minimum dynamic force of 15,000 pounds. The aggregate base should then be placed and compacted to a firm, non-yielding condition. Procedures A hand auger boring was drilled at each site with a 1'/2-inch-diameter hand auger. The borings were advanced in 4- to 6-inch increments to depth of 7 feet below the ground surface. The auger was withdrawn from the borehole after each advancement to obtain soil cuttings. The dynamic cone penetrometer (DCP) tests were completed in general accordance with ASTM International Standard Test Method D6951.