4626 HARBOR LN 2018-01-02 MF Import

Geotechnical Engineering Evaluation NGA File No.853512 Fox Residence Underpinning and Retaining Wall Design August 3, 2012 Everett, Washington page 9 up to 8.0-foot high total retaining wall with geogrid-reinforced till and Compac Keystone blocks. A geogrid-reinforced wall detail and construction notes are shown in Figure 7. The retained fill zones should consist of granular material compacted to structural fill specifications. We understand that the fill will be placed level or slightly sloping behind the wall and extending back towards the house. The drainage system, as indicated on the detail, should be installed along the base of the blocks and behind the Keystone facing. The block facing should consist of Compac Keystone blocks. The block facing should be placed on a minimum of 4-inch thick crushed rock leveling pad placed over competent native soils. The subgrade should be benched level and compacted to a non -yielding condition before placing the blocks or backfill. If loose, undocumented fill soils are encountered at the foundation subgrade elevation of the retaining wall, we recommend that the foundation area be over -excavated down to medium dense or better native soils. A drainage blanket of 12 inches of free -draining crushed rock should be placed between the blocks and the retained fill zone. The bl. ck cavities should also be filled with the crushed rock. A rigid, perforated drainpipe embedded in a minimum of 1-foot of pea gravel and wrapped in a filter fabric should be placed at the bottom of the drainage blanket. The drain should be sloped to drain into a permanent discharge point placed at the bottom of the slope. If the drain cannot be extended to the bottom of the slope, the wall drain along with all drains within this property should be discharged into a level spreader to be located at the approximate location shown on figure 8. Stratagrid 200 geogrid (or equivalent) is recommended to be used in the geogrid-reinforced fill wall design. The geogrid should be cut to the recommended lengths, attached to the blocks as recommended by the manufacturer, and extended back into the reinforced fill zone. The grid should be pulled tight before the fill is placed over the geogrid. Care should be taken not to damage the geogrid by operating construction equipment on the exposed grid, or by allowing large rocks to be placed directly on the grid. We reconunend that the pin piles for the garage foundation support be installed before the undocuntentc fill is removed and new retaining wall constructed. Structural Fill General: Fill placed behind the planed wall, beneath foundations, slabs, pavement, or other settlement - sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a NELSON GEOTECHNICAL ASSOCIATES, INC.