1209 MADRONA AVE 2016-11-17 - Laserfiche WebLink

Geote�hnical Engineering Ev�luation Packer Property Retaining ��alls and Steep Slope Evaluation Everett, Washington NGA File No. 870113 March I 1, 2013 Page 4 We measured slope inclinations below the lawer western tier of the ��alls in the recent landslide area to be approximately 20 to 60 degrees (36 to 173 percent), as sha��n an Cross-section A-A" in Fi�ure 3. I'he landslide exposed undocumented fill directly below the wall closest to the slide scarp with der�se sand and silt soils within the lower portions of the slope. Debris froin the recent landslide was deposited at the toe of the slope near the railroad tracks. The rernaining portions of tl�e steep slope are vegetated with young to mature trees and dense underbrush. We did not observe signif cant indications of recent instability within the steep slopes outside of the landslide area. However, we did observe groundwater emitting from the face of the slope near the walis alang the western property line. We were informed that tius groundwater is generally observed year round vs�ithin this area. There are five tiers of concrete block reiaining walls that were constructed alang the steep ravine slope to tiie northwest of the existing residence. Tlie blocks used for the construction consisted af Diamond �3locks. The walls range from approxima#ely 3.fl to 6.4 feet tall. Vv'e understand thai the lower twa walls wzre founded on reinfarced concrete foundations with 6-inch diameter, 4.0-foot cleep concreie piers that were placed at approximately 3.0 to 4.0 feet on-center. Robert Packer informed us that the up�er three ��ra11s were founded on the native soils. We understand that an 8- to 10-i�ich crushed rock drainage layer alang ��ith a 4-inch perforated corrugated ttrain was placed behind each of the walls. These wall d.rains along with drains associated with the residence were tightlined through a series of pipes to daylight on the steep slape below the lower walls. A gutter was also formed into the foundation of the Iower western wall with a catch basin. During our site visit, we observed groundwater emitting from the slope along the western property line that vvas captured and routed to this catch basin. These drains from the wall and catch basin then descend down the slope and outfall near the toe of the steep slope along the railroad tracks. During our site visit on February 1, 2013, we heard water flowing through these pipes a.ud observed ��rater discharging from the pipes near the toe of the slape. The reulaining portia�s of the wall were backfilled with on-site soils. SuE�st��-face Conditions Geology: The gealogic units for this area are shou��1 on the Geologic Ma�of the Everett 7.5-Minute Quadran�le, Snohomish County, VJashin on, by James P. Mznard (U.S.G.S., l 985). The site is mapped as Qtb (Transitional Beds). The Transitional Beds unit is described as a deposit of clay, silt, and very fine sand. Our explorations encountered silty sand and silt generally consistent with the description of Transitional Beds. NELSD/d GEOTECKNICAL ASSOCIATES, INC.