8925 AIRPORT RD MUKILTEO SCHOOL DISTRICT 2022-01-19

GeoTest Services, Inc. February 26, 2018 Mukilteo SD —Wall Design, Everett, Washington Job No. 18-0068 The groundwater conditions reported during field explorations are for the specific locations and dates indicated, and therefore may not necessarily be indicative of other locations and/or times. Groundwater levels and / or seepage rates are not static and it is anticipated that groundwater conditions will vary depending on local subsurface conditions, season, precipitation, changes in land use both on and off site, and other factors. We recommend that GeoTest personnel monitor construction of the retaining wall and that contingencies for differing site conditions be incorporated into the project contract documents to allow for necessary changes in design and construction methods. It should be anticipated that temporary dewatering may be required during the construction phase for this project. Modular Block Gravity Wall Design A gravity retaining wall has been designed for construction primarily using modular wall blocks, typically 2.5' x 2.5' x 5', with suitable native Glacial Till and/or imported structural fill being used to backfill behind the wall. If import backfill is to be used, we recommend a WSDOT 9-03.14(1) Gravel Borrow. Other block sizes and shapes are available as needed through the manufacturer. The wall is planned to be constructed vertical (no batter). For typical manufacture change of direction corner details, please see the attached Figures 5 and 6. A scaled model of block configuration may be found in Figure 7. The wall should be founded on a minimum 6 inch thick compacted crushed stone base pad and the bottom of the base block should be buried as indicated in the table below to provide kick -out resistance at the toe of the wall. GTS recommends a 3 foot minimum horizontal bench in front of the wall. The wall was designed with sufficient block mass to resist forces and moments acting to slide and overturn the wall. Proper wall drainage is necessary in maintaining a stable wall. The clear crushed rock (no fines) drainage layer located behind the wall, as shown in Figures 3 and 4, should consist of a triangle with a 1 H:1V slope up from the base of the wall to within approximately 1 foot of the top of the wall and wrapped with a non -woven geotextile fabric such as Mirafi 140N or performance equivalent. Design Assumptions: Traffic surcharge: Type D school bus: 30 kip gross vehicle weight with a 30 foot front to back wheel base and 8.5 feet wide. In areas with sufficient Right -of -Way to grade slopes at a maximum of 2 horizontal to 1 vertical 2HAV to "catch" existing ground, GTS recommends this option in lieu of retaining wall construction. The table below presents wall configurations with associated minimum embedment depths: Page 3 of 8