1617 EDGEMOOR LN 2016-11-10 - Laserfiche WebLink

McKinnon Residence Retaining Wall NGA File No 910614 1617 Edgemoor Lane December 2, 2014 Everett, Washington Page 8 location. 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. In addition to the minimum recommended embedment into the native material, the piles should be driven to a refusal criterion of less than one inch of movement during 60 seconds of continuous driving. The wall lagging should be embedded a minimum of 12 inches into the finished slope face. Metal plates should be welded to the back of the pin piles to allow a connection for the timber lagging. We recommend that the voids behind the wall be backfilled with 2-inch crushed rock up to the top of the retaining wall. For the 2-inch crushed rock, the shoring wall should be designed to resist a lateral load resulting from a fluid with a unit weight of 45 pounds per cubic foot (pcf). These loads should be applied across the pile spacing above the excavation line. The active pressure could be partially resisted by passive resistance acting on the below -grade portion of the piles. The passive resistance could be calculated based on a 120 pcf equivalent fluid density acting on two effective pile diameters below the base of the exposed portion of the wall. This value incorporates a factor of safety of 2.0. The upper five feet of pile embedment should be neglected when calculating the passive resistance due to the presence of loose material on the slope. If tiebacks are utilized in the wall design, we recommend that all later pressures be transferred to the tiebacks. A uniform surcharge of 8H should be applied to the wall design to account for seismic loading, where H is the exposed height of the wall. For portions of the retaining wall directly supporting the proposed garden shed, we recommend that an additional 50 pounds per square foot (psf) uniform surcharge be included in the design. 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. The portions of the wall in the approximate location of the proposed garden shed may need to be supported laterally due to the increased wall heights and the surcharge loads from the proposed shed. We recommend that if needed, these lateral pressures be resisted by tieback anchors. We also recommend that an alternative to the tieback anchors within this portion of the wall may consist of concrete ecology block deadman anchors connected to the wall and buried in the wall backfill. If this alternative is deemed desirable during the retaining wall design, we can provide further details regarding this option at that time. NELSON GEOTECHN/CAL ASSOCIATES, INC.