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Geotechnical Engineering Report <br /> Staples Rockery Failure Everett, Washington lierracon <br /> March 8, 2019 Terracon Project No. 81175122 <br /> Fill Type WSDOT Standard <br /> Specification Acceptable Location for Placement <br /> 9-03.12(1)A Gravel Backfill for <br /> Foundations Class A <br /> Structural Fill 9-03.9(1) Ballast Beneath and adjacent to the retaining wall <br /> 9-03.9(3) Crushed Surfacing <br /> Base Course <br /> 4.2.4 Compaction Requirements <br /> Item Description <br /> 8 inches or less in loose thickness when heavy, self- <br /> Fill Lift Thickness propelled compaction equipment is used <br /> 4 inches in loose thickness when hand-guided equipment <br /> (i.e.jumping jack or plate compactor) is used <br /> Upper 2 feet of fills: Minimum 95%of the material's modified <br /> Proctor maximum dry density(ASTM D 1557) <br /> Minimum Compaction Requirements <br /> Deeper than 2 feet of fills: Minimum of 90%of the material's <br /> modified Proctor maximum dry density(ASTM D 1557) <br /> Moisture Content—Granular Material Workable moisture levels' <br /> 1. Typically within 2%of optimum <br /> 4.2.5 Grading and Drainage <br /> Surface water drainage should be controlled to prevent undermining of structures during and after <br /> construction. Gutters and downspouts should be routed into tightline pipes that discharge into a <br /> municipal storm drain or other suitable location. <br /> 4.2.6 Construction Considerations <br /> Several construction-related factors may result in further failure of the existing rockery. To reduce <br /> the risk of such failures, the contractor must exercise care during construction. At minimum, these <br /> considerations should be incorporated in the contractor's work plan and implemented during <br /> construction: <br /> Surcharging and vibrations. Equipment and stockpiling should be limited to only what <br /> is immediately necessary to construct the current lift of the retaining wall. Excessive <br /> surcharging and vibrations may destabilize the rockery. <br /> Construction sequencing. The sequence in which work will be performed is critical for <br /> deconstructing the existing rockery in a manner that will not result in further ground <br /> displacement or erosion of the right-of-way. The sequence will require removing the <br /> existing rockery in short, 2 to 3-foot lifts or the dimension of the rockery rocks, whichever <br /> is greater, and immediate placement of temporary wood lagging between soldier piles to <br /> I <br /> Responsive • Resourceful • Reliable 8 <br />