1215 MADRONA AVE 2016-08-24 - Laserfiche WebLink

1 ' , 1 ' 1 ' ' 1 ' 1 1 1 1 ' ' 1 Gustafson Residence Retaining Wall NGA File No 9241 l 5 1215 Madrona Avenue June 12, 2015 Everett, Washington Page 3 concrete slab. The property is bordered to the north by the Burlington Narthern Santa Fe Railroad Right- of-Way, to the east and west by residential properties, and to the south by Madrona Avenue. We measured slope inclinations on the steep slopes below the rear yard area and concrete rubble walls to be approximately 31 to 43 degrees (60 to 93 percent), as shown on Cross-section A-A' in Figure 3. The concrete rubble walls are immediately above the steep slope that previously experienced the landslide and area that has recently been stabilized. We did not observe indications of additional significant sliding within the steep slopes in the vicinity of the recent landslide area and concrete rubble walls. However, some settlement was observed in the vicinity of the concrete rubble walls. We also observed groundwater emitting from tl�e face of the slope along the eastern property line below the proposed wall area. We understand that this groundwater is generally observed year round within this area. As a part of the previous drainage repairs within the site, we understand that the residence drains were tightlined into a new drain that descends down the slope within the northern portion of the property. A 4- inch corrugated pipe was observed to daylight at the top of slope and extended down the face of the slope to the north. We understand that the pipe outlets near the railroad tracks to the north of the property. Subsurface Conditions Geology: Geology: The geologic units for this area are shown on the Geolo =i�, c Map of the Everett 7.5- Minute Quadran�le, Snohomish County, Washington, by James P. Minard (U.S.G.S., 1985). The site is mapped as Qtb (Transitional Beds) with Qva (Advance Outwash) deposits mapped in the vicinity of the site. The Transitional Beds unit is described as a deposit of clay, silt, and very fine sand. The advance outwash deposits are described as clean, mostly gray sand with pebbles and cobbles. Our explorations encountered fine to medium sand witl� gravel and varying amounts of organics interpreted to be undocumented fill and native advance outwash soils underlain by brown to gray sandy silt interpreted as native transitional bed deposits. Explorations: The subsurface conditions within the site were explored on May 11, 2015 by drilling two borings to a deptl� of 21.5 feet below tl�e existing ground surface using a portable, limited-access drill rig. The approximate locations of our explorations are shown on the Schematic Site Plan in Figure 2. A geologist from Nelson Geotechnical Associates, Inc. (NGA) was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and NELSON GEOTECHNICAL ASSOCIATES, INC.