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

Oskar Property Deck Limited CAO,Everett,WA Materials Testing&Consulting,Inc. July 17,2019 19B182 Subsurface Soil and Groundwater Conditions: Subsurface conditions at the location of the proposed deck foundation and within the adjacent yard towards the slope crest were assessed by DCP testing, and soil and groundwater conditions were observed directly via a supplemental hand-auger boring (Appendix C). Soil conditions throughout the project site were generally consistent between the exploratory locations, representing varying depths of loose to medium dense cover soils and weathered glacial deposits overlying dense or hard glacial till. DCP-1 was advanced at the approximate location of the northern corner of the proposed deck, at or just slopeward of the northernmost footing closest to the slope. Soil conditions at DCP-1 were observed to be generally medium dense from the surface but gradually decreasing in density until loose from about 4.0 to 4.5 feet BPG. Immediately underlying the loose interval, soils became progressively dense until refusal at 7.3 feet BPG, and were generally dense or hard below about 5.7 feet BPG. DCP-2 was advanced at the approximate western corner of the proposed deck footprint near the current rhododendron bushes. Soil conditions at DCP-2 were recorded to be loose to very loose (medium stiff to very soft)to approximately 3.0 feet BPG. Underlying these loose (soft) cover soils we recorded abruptly dense deposits through approximately 4.5 feet BPG upon reaching practical refusal. DCP-3 was located near the crest of the critical slope adjacent to the chain-link fence and directly north of the proposed deck footprint. In this location, we found a notably greater thickness of variable upper deposits. Soils were recorded as medium dense to about 3 feet depth, then became loose to very loose (soft) to approximately 6.7 feet BPG. Below the loose conditions, density gradually increased from medium dense to dense by 9.0 feet BPG. Testing reached practical refusal at about 10 feet BPG. This result appears to be a local anomaly in comparison to other current and past test results, and may represent either natural variation or local grade fills placed along the crest during original site grading. DCP-3 (2016) located northwest of the deck also along the slope crest found a more typical profile of approximately 3 feet of variable cover soils over progressively dense or hard conditions below. Supplemental hand-auger soil observations at HA-1 at the outer extent of the proposed deck were broadly consistent with data and interpretations from DCP tests as well as geologic literature sources. At HA-1, we did not find obvious grade fill soils, although native-sourced sandy fill materials can often be indistinguishable from in-place native deposits. Within HA-1, underlying shallow silty topsoil was silty sand with varying amounts of gravel to 3.0 feet BPG found in a variably loose to medium dense condition. Below the sandy cover soils, we observed a generally fine-grained soil in a stiff to very stiff condition until reaching practical refusal at 3.5 feet BPG on an obstruction. The end depth was above the depth of dense soils at DCP-1, but similar to the profile of DCP-2. We interpret the soils at end depth within HA-1 to be the upper weathered extent of glacial till deposits anticipated to harden with depth. 4J�(./