4702 W GLENHAVEN DR 2020-06-16 - Laserfiche WebLink

Oskar Property Deck Limited CAO,Everett,WA Materials Testing&Consulting,Inc. July 17,2019 198182 The DNR Interactive Geologic Map displays compiled landslide information gathered by the DNR from various existing maps and internal project data. There are no mapped landslide features or mass-wasting deposits in the vicinity of the project site. The nearest landslide mapped is over 1/4-mile away to the northeast, and based on extent appears to be a localized feature. Several larger landslides deemed dormant or relict are mapped further away to the northwest. Review of Lidar imagery hosted by the DNR indicates the slope below the site to be roughly planar from top to base, ''exhibiting no obvious failure features of concern at present or from the recent past. Discussion and Recommendations: Construction Feasibility The findings of MTC's hand-operated subsurface explorations focusing on the proposed deck footprint and our site reconnaissance of the project area appear consistent with available geologic literature, and indicate the proposed deck construction at the planned location is feasible given suitable site-specific design and construction measures are applied and by following the guidelines and recommendations presented below. Dense glacial till soils are interpreted to be present at levels between about 3.5 and 5.0 feet BPG within the proposed deck building area, and locally deeper along the slope crest. The improvement area maintains a minimum 20-foot setback from the slope crest, with the closest isolated foundations planned to be a few feet additional distance away (under a cantilever scenario) as well as embedded below surrounding surface grade which will increase their effective setback from exposure to around 30 feet. This proposed horizontal setback appears to be viable from a geotechnical perspective given the underlying soil conditions available for foundation support, and is in accordance with typical International Building Code (IBC) specifications for minimum foundation distance from bordering slopes (at least H/3 distance). Given the conditions documented herein, the site appears to be in suitable condition for the proposed improvements assuming proper design and management is applied, as well as incorporation of the recommendations below including specifics for foundation placements. We presume new deck foundations will consist of isolated elements (spread footings, pier blocks, pillars, etc.) embedded for lateral support as addressed below, and that site disturbance will be limited to the area immediately around the existing deck, coming no closer than about 20 feet from the upper slope crest. MTC provides the following site- and development-specific recommendations to be followed to permit the proposed deck reconstruction and reduce the inherent risks of implementing the proposed improvements within the vicinity of a geologically sensitive critical area slope. In the event that additional information is required for design, MTC recommends we be contacted for geotechnical engineering consultation and analysis as appropriate to address the proposed design. 62(