1618 HOLBROOK AVE 2018-01-02 MF Import

Retaining Wall Letter Lyashuk Residence, Everett, WA January 29, 2007 NGA File No. 755806 Page A CONCLUSIONS AND RECOMMENDATIONS It is our opinion that from a geotcchnical standpoint the planned temporary ultra block wall is feasible. An ultra block is a cement block 2.5 feet wide, 2.5 feet tall and 5 feet long with an interlocking design between the stacked blocks. The medium dense or better native soils should provide suitable foundation support for the temporary ultra block wall. We recommend that the wall subgrade excavation be advanced to expose be mcaimn dense or better native soil. A six-inch thick layer of crushed rock should be compacted over the subgrade soil. We understand that the south wall of the planned residence will be a concrete retaining wall constructed adjacent to the ultra block wall, and the space between the walls will be backfilled. We recommend that a wall drain he incorporated into the project plans behind the permanent concrete retaining wall. General recommendations for retaining wall drainage have been included in this letter. We recommend that the permanent concrete retaining wall constructed for the south wall of the residence extend at least two feet above the finished ground surface to provide a catchment area for material that may slough from the slope on the adjacent property. We have included recommendations for the concrete retaining wall design in this le6er. Ultra Block Wall Design and Construction Recommendations The maximum height of the planned ultra block wall is expected to be 12.5 feet, including a minimum recommended embedment of one -foot into native soils. We have provided a design for a 12.5-foot-high ultra block retaining wall. The wall detail and design parameters along with construction notes are shown on Figure 6. We have assumed that the area behind the wall will be filled with clean rock spalls or drain rock. Excavated soil should not be used as fili behind the wall. The backslope behind the wall should be equal to or flatter than tLL preconstruction slope angles, and a drainage system, as indicated on the detail, will be installed along the base of ultra block facing. The ultra blocks and drain materials should be available on site prior to further excavation at the toe of the slope. The cut should be sloped or benched is needed for temporary stability and wall construction should be accomplished immediately after excavation. The ultra block wall should be constructed with a batter of approximately I Horizontal to 9 Vertical NELSON GEOTECHIJICAL ASSOCIATES, INC.