1209 MADRONA AVE 2016-11-17 - Laserfiche WebLink

Geotechnical Engineering Evaluation Packer Property Retaining Walls and Steep Slope Ez�aluation �verett, Washington NGA File No. 870113 March l l, 2013 Page 1 l �tetair�ing V4'ati Besign and Constructian Tlie proposed new retaining ��all should consist of 3-inch square driven steel tubing bridged using pressure-treated timber Iagging and anchored back into the slope using grouted or mechanical anchors. The new retaining wall shauld be located wiihin the ravine immediatel}� bela�J the existing lower western block �-all. The finai extent and heights of the wall should be detennined in the field based on site conditions. I-Ic�wever, u�e recommend that the exposed portion of the wall not exceed ei�ht feet in height. T1�e approximate ]ocatioz� of the pr�posed retainin.g wall is shown on the Schematic Slope Stabilization Site P3an in Figure 6. The retaining wall should be designed by an experienced structural engineer licensed in the SLate of Washington. ��e recamrnend that the square iubing piles be galvanized extra strong (Schedule 80) steel pipe sections driven into place using a hand-held, 144-pound jackhammer or larger. The piles should be spaced at a naaximum distance af four feet, and should be embedded a minimum of 15 feei into the competent slope znaterial. The ma�imum spacing and minimunl en�bedrnent values are to provide add'rtional reinforceznent to the slope and Iessen the potential for sliding. Piles that do not mect t�us minimum embedment criterion should be rejected, and replacement piles should be dr�ven after consuiting with the structural engineer on the new pile locations. Our e�;plorations encountered loose tuidocumented �lis within the planned areas to be repaired. If large particles ar debris are present within the fill, there is a passibility tl�at this material may obstruct some piles at shallow depths. There should be contin�encies in the budget and desi�,m for additional/relocated piles to replace piles that may be nbstructed by debris in the fiil. In addition to the minimum recommended embedment into the nat3ve material, the piles shauld 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 inclies 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.SH:1 V. The spalls should be extended up to the bottom of the existing block wall. For the 2- to 4- inch rock spalls, the shoriag wall should be designed to resist a iateral load resultinb from a fluid with a unit weight of 45 pounds per cubic foot (pc�. These loads shouid be applied across the pile spaczn� above tl�e excavation 1ine. These loads should mostl}f be resisted by the tiebacks as recommended in the '�'iebacks subsection of this letter, but can be additionally resisted by a passive �aressure of l24 pef applied on two-pile diameter under the excavation line. This value of the passive pressure incor�orates a NELSC}� GEQTECHId1C/�L .�4SSE?Ci.r47"ES, il�C.