1209 MADRONA AVE 2016-10-05 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No. 870113 Packer Property March 11,2013 Retaining Walls and Steep Slope Evaluation Page 11 Everett,Washington Retaining Wall Design and Construction The proposed new retaining wall should consist of 3-inch square driven steel tubing bridged using pressure-treated timber lagging and anchored back into the slope using grouted or mechanical anchors. The new retaining wall should be located within the ravine immediately below the existing lower western block wall. The final extent and heights of the wall should be determined in the field based on site conditions. However,we recommend that the exposed portion of the wall not exceed eight feet in height. The approximate location of the proposed retaining wall is shown on the Schematic Slope Stabilization Site Plan in Figure 6. The retaining wall should be designed by an experienced structural engineer licensed in the State of Washington. We recommend that the square tubing piles be galvanized extra strong (Schedule 80) steel pipe sections driven into place using a hand-held, 140-pound jackhammer or larger. The piles should be spaced at a maximum distance of four feet, and should be embedded a minimum of 15 feet into the competent slope material. The maximum spacing and minimum embedment values are to provide additional reinforcement to the slope and lessen the potential for sliding. Piles that do not meet this minimum embedment criterion should be rejected, and replacement piles should be driven after consulting with the structural engineer on the new pile locations. Our explorations encountered loose undocumented fills within the planned areas to be repaired. 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. We recommend that the wall be backfilled 2-to 4-inch rock spalls with a maximum final slope inclination of 1.5H;1 V. The spalls should be extended up to the bottom of the existing block wall. For the 2-to fl- inch rock spalls, 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. These loads should mostly be resisted by the tiebacks as recommended in the Tiebacks subsection of this letter, but can be additionally resisted by a passive pressure of 120 pef applied on two-pile diameter under the excavation line. This value of the passive pressure incorporates a NELSON GEOTECHNICAL ASSOCIATES, INC.