4920 EVERGREEN WAY STAPLES Geotech Report 2022-10-25

Geotechnical Engineering Report lierracon Staples Rockery Failure Everett,Washington March 8, 2019 Terracon Project No. 81175122 Item Description The area of interest exists between a paved residential street (Glacier Lane) Existing and the west wall of the existing building with a failing rockery located along Improvements the property line/street right-of-way and that parallels the adjacent building wall. Other existing features include overhead utilities, fencing and railing between street and rockery. Current Ground Cover The area behind the rockery(within the street right-of-way) is paved asphalt and grass Existing Topography 111 (Boundary Survey by West of the rockery, grades are relatively level at an elevation of about 328 Terramark, 2018) feet. The rockery is approximately 24 feet at the maximum height. 2.2 Project Description Item Description Architectural drawings of the Staples building, which is immediately east of the rockery, developed by Hall Associates dated May 11, 1973. Supporting Boundary survey by Terramark performed on January 12, 2018. Information Meeting with City of Everett, January 20, 2018 to discuss feasibility of retaining wall options. Approximately 180 feet of rockery parallels a building wall with the southern half of the building wall designed as a retaining structure and the northern half as a typical building wall not designed for soil loading. An approximate 20-foot section of the rockery has recently failed and contacts the portion of Project Description the building wall not designed for soil loading. This section of building wall was not designed to support the retained soil and stabilization options to replace this section of rockery are to be evaluated. Further displacement or movement of the rockery could impact the City of Everett street right-of-way or the existing building wall. A retaining wall to stabilize the northern half of the building wall (i.e. approximately 90 feet)that is at immediate risk from the failing rockery. The retaining wall will likely need to extend further to the south to protect against any future failure of the portion of the rockery adjacent to the south half of Proposed Structure the building that could impact the Glacier Lane right-of-way if the rockery were to fail. The retaining wall design is assumed to be a soldier pile and tieback system with temporary wood lagging and a permanent concrete facing. The wall would be located within the adjacent City right-of-way and permanent easements will be needed from the City of Everett for the wall and tieback anchors. Below Grade We anticipate that the soldier piles will be embedded up to 10 feet or more Structures below the base of the existing rockery wall. Pavements We assume construction of the retaining wall can be performed without the need to repair or replace the residential street adjacent to the wall. Responsive ■ Resourceful • Reliable 2