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Gr@O Engineerfng Consultants Inc <br /> P 4 Box 21490Minneapolis MN 55421 <br /> Phone 763 502 9945Fax 763 502 9946 <br /> Febn�ary 19,2008 <br /> Mr.Brian Gallagher <br /> Atlas Foundation Company <br /> P.O.Box 117 <br /> Rogers,MN 55374 <br /> ; RE: Drive Head Calibrations <br /> ' Rogers, Minnesota <br /> Project Number: 007-0075-5374.1 <br /> This report contains the results of a total of 29 calibrations of several hydraulic drive heads used <br /> for installation of he(ical anchors. The heads are identified as 4000, 6000, 9000, 10,000, 12,OQ0, <br /> I 5,000 and ]8,OOQ foot-pound torque heads. T'he majority are models by Power Systems. A few <br /> are models by two-speed types by Pengo and Pro-dig,and are indicated, respective3y. The heads <br /> were attached to various machines including Bobcat models T250 and MT52; John Deere <br /> models 590D;New Holland model LS 170; and Caterpillar models 312 and 314. <br /> The calibrations were conducted at the Atias Foundation Company yard near Rogers,Minnesota <br /> on December 18,2007_ Although subsurface c�ploration data was not available at the site,the <br /> soil conditions in the area typically consist of sandy lean clay rill underiain by sand and gravel <br /> glacial outwash. <br /> The system was ca(ibrated by rotating and advancing a helical anchor into the ground at normal <br /> operating speed. The gauge pressare of the operating hydraulic system was cornpared to the <br /> torque measured on a torque indicator identified as Chance E7Z W-38537. We understand thc <br /> torque indicaxor was recently calibrated. <br /> The results for each cirive head and machine combination were plotted aad a best fit line of tLle <br /> data was computer generated using linear regression by the method of least squares. The results <br /> have been tabulated in chart foim. The charts also show the slope(m) and y-intercept(b)of the <br /> best fit line so torque at gauge pressures not shown on the chart may ba determined,by <br /> multiplying the gauge pressure tiroes the slope (m)of the line and adding/subtracting the y- <br /> intercept(b). Copies of the charts are attached. <br /> The charts also include working load and ultimate capacity for each pressure measurement. The <br /> warking load includes a safety factor of 2.0. T7ie ultimate capacity calculations are based on a <br /> ►•atio of 10 to 1 between the normaiized torque a�id the ultimate load, a value that is typically <br /> used for the soils in this area. <br />