1901 W MUKILTEO BLVD Geotech Report 2022-10-25

Scriven Residence Improvements-REVISED NGA File No 974316 1901 West Mukilteo Boulevard November 29,2016 Everett,Washington Page 12 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 anchors such as,helical anchors. We recommend that five percent of the anchors, but no less than two anchors, be treated as performance anchors and be tested to a minimum of 200 percent of the design loads. The soil creep characteristics would be evaluated during these tests. We recommend that the foundation embedment of the residence and utilities within the yard area be verified by the contractor and measurements made in the field at the time of tieback installation to ensure tiebacks do not encounter the existing residence, or underground utilities. No-Load Zone: The anchor portion of all tiebacks must be located a sufficient distance behind the wall face to develop resistance within a stable soil mass. We recommend the anchorage be obtained behind an - assumed no-load zone. The no-load zone is defined by a line extending horizontally from the base of the wall back towards the residence a distance of four feet. The line should then extend up from the base elevation at an angle from the horizontal of 60 degrees. We expect that some undocumented fill may exist beyond the no-load zone. We therefore recommend that the bonded portion of the tiebacks, or the helical anchor helicies,be placed a minimum of 15 feet beyond the face of the wall. We recommend that we monitor soil conditions during anchor installation in order to evaluate adequate penetration into competent soils. NELSON GEOTECHNICAL ASSOCIATES, INC.