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GeoTest Services, Inc. <br />Mukilteo SD —Wall Design, Everett, Washington <br />February 26, 2018 <br />Job No. 18-0068 <br />Table 1: Ultrablock° Gravity Wall <br />For Flat Backslope and Traffic Surcharge <br />Total Wall Height <br />Location <br />Base Width <br />Orientation <br />2.5 feet <br />1st row (base) <br />2.5 feet <br />Parallel to Wall Face <br />5 feet (Figure 4) <br />1st row (base) <br />2.5 feet <br />Parallel to Wall Face <br />2rd row (top) <br />Parallel to Wall Face <br />7.5 feet (Figure 3) <br />1st row (base) <br />7.5 feet <br />Parallel (1) + Perpendicular (1) <br />to Wall Face <br />2nd row (middle) <br />Parallel to Wall Face <br />3rd row (top) <br />Parallel to Wall Face <br />* Note: For 7.5 foot high wall, the first row (base block) must be turned -in and <br />placed (perpendicular) to the wall face. <br />All walls have a cap block installed at the top. However, they are not intended to function <br />as a wheel (curb) stop. <br />Gravity Wall Construction Considerations <br />Key elements in the construction of a stable wall include the following: <br />• The wall section must be founded on suitably firm and unyielding soils. <br />Undisturbed, medium dense to dense native soil or suitable placed and <br />compacted structural fill placed over undisturbed native soil, should provide <br />adequate bearing capacity for the wall foundation. <br />• The exposed wall base subgrade surface should be observed and evaluated by <br />GeoTest personnel under the direction of the geotechnical engineer to ensure <br />that our design assumptions are met. The crushed rock base can then be placed <br />and compacted. <br />• We recommend that the wall be embedded a minimum of 12 inches below the <br />grade in front of the wall. Fill used to backfill in front of the constructed walls <br />should consist of approved native soil or import granular material that is <br />compacted in place. <br />• Drainage is essential for proper performance of retaining walls. The wall design <br />assumes drained conditions and does not allow for hydrostatic pressure buildup <br />behind the wall. GeoTest recommends 12 inch drainage layer constructed <br />immediately behind the wall consisting of WSDOT Specification 9-03.12(4) <br />Gravel Backfill for Drains or other engineered approved free draining material. <br />GeoTest recommends that this material be fully wrapped on three sides with <br />geotextile separation fabric (Mirafi 140N or performance equivalent) in order to <br />reduce siltation and clogging of the drainage layer. The geotextile fabric should <br />not extend up the back face of the wall. <br />Page 4of8 <br />