4937 SEA BREEZE WAY 2017-01-13 - Laserfiche WebLink

� Geotechnical Engineering Evaluation Pepe Rctaining Wall Everett, Washington � NGA File No. 916915 April 27, 2015 Page 6 The Transitional Bed soi] interpreted to form the core of the steep slopes are considered stable with respect to deep-seated slope failures. All steep slopes have the potential for shallow sloughing failures during seismic events. During our initial site visit, we observed evidence of slope instability to the south of the existing residence. A retaining wall may be needed on that side to prevent future sliding. Erosion Hazard The critcria used for determination of erosion hazar�d areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is relatcd to the vegetative cover and the speciiic surface soil types, which are related to the underlying geologic soil units. The Soil Sut•vev of Snohomish Countv Area, Washin�ton, by the Soi] Conservation Service (SCS) was reviewed to deter�nine the erosion hazard of the on-site soils. The site s�irface soils were classified using the SCS classitication system as Alderwood-Everett gravelly sandy loam, 25 to 70 percent slopes. "1'hese soils are listed as having a moderate to high erosion hazard. CONCLUSIONS AND RECOMMENDATIONS General 1t� is our opinion that the wall has serious issues ai�d failed due to a coinbina�tion of factors including the stress rods detaching froir� wall, picrs, and the deadman anchor; poor till material behind the wall; and poor drainage of Yhc housc and property. Also, the plastic wal] lagging has deteriorated. There is evidence of ground settlement in walkways, the garage, and a post supporting the roof due to the tailure of thc wall and thc wall backfill. A structural engineer will nced to evaluate the wall and fully understand the as-built conditions in order to decide if the wall can be saved and a repair implemented. (f the structural engineer decides th�t the wall can be fiaed, we have provided design reco�r�mendations and parameters in the Retaining Wall Repair or Replacement s�ibsection of this report. I l� it is deemed that the wall cannot be repaired, we should be contacted to discuss options for a new retaining wall. We observed a signifiicant severely leaning tree on the slope to tl�e so�itheast of the residence. This tree is severely bowed and ]eaning towards the house. We recommend that this tree be evaluated by an arborist and removed so it does not damage the house should it fail. The tree should be removed down to the stump, but the st�>>�p should not be re��oved, as removing it wo�ild cause majoe slope instability. NELSON GEOTECHN/CAL ASSOCIATES, INC.