4110 CLIFF DR 2022-01-26 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No. 1021318 Cliff Drive Short Plat Residence Development February 2, 2018 Everett, Washington Page 5 CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned residence development within the site is feasible from a geotechnical standpoint. It is also our opinion that the soils that underlie the site and form the core of the site slopes should be stable with respect to deep-seated earth movements, due to their inherent strength and slope geometry. Proper erosion and drainage control measures as recommended in this report should reduce this potential. Our explorations indicated that the site is underlain by surficial undocumented fill soils with medium dense or better native glacial soils at depth. These glacial soils should provide adequate support for foundation, slab, and pavement loads. We recommend that the structures be designed utilizing shallow foundations. Footings should extend through any loose surficial soil and be keyed into the underlying competent native soils. These soils should be encountered roughly one to three feet below the existing ground surface. We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require additional excavations in foundation, slab, and pavement areas to remove the unsuitable soils. We also recommend that the downhill western foundation lines be additionally embedded a minimum of two feet into the competent native glacial soils. All other structure foundations can utilize standard foundation embedment depths. All grading operations and drainage improvements planned as part of this development should be planned and completed in a matter that enhances the stability of the site slopes, not reduces it. Excavation spoils associated with the residence excavations should not be stockpiled near the site slopes or be allowed to encroach on the slopes. Also, all runoff generated within the site should be collected and routed into a permanent discharge system and not be allowed to flow over the slopes. Future vegetation management on the slopes should be the subject of a specific evaluation and a plan approved by the City of Everett. The site slopes should be monitored on an ongoing basis, especially during the wet season, for any signs of instability, and corrective actions promptly taken should any signs of instability be observed. Lawn clipping and any other household trash or debris should never be allowed to reach the slopes. The soils encountered on this site are considered moisture -sensitive and will disturb easily when wet. To lessen the potential impacts of construction on the slopes and to reduce cost overruns and delays, we recommend that construction take place during the drier summer months. If construction takes place during the rainy months, additional expenses and delays should be expected. Additional expenses could include the need for placing erosion control and temporary drainage measures to protect the slopes, the need for placing a blanket of rock spalls on exposed subgrades, and construction traffic areas prior to placing structural fill, and the need for importing all-weather material for structural fill. NELSON GEOTECHN/CAL ASSOCIATES, INC.