1907 W MUKILTEO BLVD 2021-11-15 - Laserfiche WebLink

I • • Pearson Property Slope Stabilization NGA File No 945216 1907 West Mukilteo Boulevard February 19,2016 Everett,Washington Page 8 anchors or mechanical anchors such as helical anchors. The new retaining wall should be generally located just setback from the existing top of the steep slope along the entire width of the property. The final extent and heights of the new retaining wall should be determined based on an accurate survey of the property. However,we recommend that the exposed portion of the new wall not exceed eight feet,but be no less than six feet. The retaining wall should be designed by an experienced structural engineer licensed in the State of Washington. The wall should be designed to resist an active pressure acting on the piles and lagging for design of the piles and should be calculated based on a triangular pressure distribution equivalent to that exerted by a fluid with a density of 60 pcf. This value is based on loads from the undocumented fill and loose soils that will remain behind the wall. A uniform surcharge of 8H should be applied to the wall design to account for seismic loading, where H is the total height of the wall. The above active load should be applied on the full center-to-center pile spacing above the base of the exposed portion of the wall. A 50 percent reduction of this value can be used for the purpose of designing the wall lagging. The active pressure should be entirely resisted by the tieback anchors. Passive resistance on the below grade portion of the piles should not be included in the design. We recommend that the piles be driven into place using a hydraulic hammer, with a minimum energy rating of at least 1,500 ft-lb. The piles should be spaced at a maximum distance of 4 feet, and should be embedded a minimum of 20 feet into the competent slope material below the fill. In addition to the minimum recommended embedment into the native material, the piles should be driven to a refusal criteria of less than one inch of movement during 15 seconds of continuous driving. Our explorations encountered loose undocumented fills within the planned retaining wall area. If large particles or debris are present within the fill, there is a possibility that this material may obstruct some piles at shallow depths. There should be contingencies in the budget and design for additional/relocated piles to replace piles that may be obstructed by debris in the fill. The wall lagging should be embedded a minimum of 12 inches into the finished slope face within the competent glacial soils. Any backfill placed behind the wall should consist of clean 2-inch crushed rock. The crushed rock should be tamped in place using hand tools to ensure all gaps are entirely filled. We should be retained to review final plans, observe test pile installation prior to finalizing design, monitor installation of the piles,and evaluate pile refusal. Tie-backs General: These systems should consist of drilled, grouted tieback anchors, or mechanically installed NELSON GEOTECHNICAL ASSOCIATES, INC.