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Hennepin County ��E� AET Project No. 09-00552 July 7, 2017 Page 3 of 4 Instruction Manual, Section 7.1.3.2 UTDUK Duckbill Guy Anchor, which requires the anchor to be installed at the same angle as the guy wires (60 degrees from horizontal). Though the County is using a screw anchor rather than the duckbill anchor, the recommended installation angle is the same. Mr. Kelly Fisher of Hennepin County indicated previous weather station towers were all installed with the anchors vertical and requested we proceed with the load test on the vertical anchor. The load was applied to the screw anchor with a chain attached to a Bobcat skid-steer loader. Refer to the photograph in the appendix for test set up. The minimum test load was 1,500 pounds which is approximately 1.5 times the design guy wire load of 990 pounds. A stringline was used to measure the horizontal and vertical movement of the anchor during and after the test. The test load varied between 1,500 and 2,100 pounds during the test and was held for 10 minutes prior to releasing the load. Measurements indicate the anchor moved 2.75 inches horizontally and 1.9 inches vertically due to the applied load on the anchor. Although the loading did not cause failure of the anchor, a significant wind event will likely cause additional movement of the anchor and slackening of the guy wires. Frost Heave The soils present on the site have a high frost heave potential. If lenses of silt are present within the soil profile, about 1 to 3 inches of frost heave may occur. Frost penetration in clay soils would be approximately 4 feet during an average winter, and 5 feet during a severe winter. Comparable frost penetration for sand soils would be about 6 feet during an average winter, and 7 feet during a severe winter. These frost penetration depths assume there is no snow cover providing insulation to the underlying ground. 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 of the proposed helical anchors, about 4.5 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. Other Recommendations We recommend at least quarterly observation of the guy wires, anchoring devices and tower base in order to detect possible movement due to frost action or settlement. An observation should also be completed after a significant wind event. 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.