3322 KROMER AVE 2023-05-26 - Laserfiche WebLink

GeoTest Services, Inc. — Revision 1 April 10, 2020 Kikuchi Retaining Wall, Everett, Washington Project No. 20-0344 .. aKY:: Subsurface Soil Conditions Subsurface conditions were explored by advancing three exploratory test pits (TP-1 through TP- 3) on March 17, 2020. The explorations were advanced to an approximate depth of 6.5 to 7.5 feet below ground surface (BGS) using a tracked excavator. The approximate locations of these explorations have been plotted on the Site and Exploration Plan (Figure 2). Subsurface conditions were similar in all three test pit locations and produced comparable results. The subsurface,profile generally consisted of a 0.75-foot layer of dark brown; silty, very gravelly sand with organic matter (topsoil) at the surface. Underlying the topsoil was a light brown, very sandy silt/clay interpreted to be. deposits of the native transitional beds. The upper 0.5 feet of the native soils displayed a weathered texture containing higher percentages of sand common with orange mottles. At approximately 3.5 to 4.5 BGS, soil color appeared to darken with an increase of moisture and the soils exhibited a blocky structure. In TP-3, the deposits of the transitional beds transitioned from the lighter light brown colored silt/clay to a denser greyish -blue clay. Subsurface conditions were also explored using a Dynamic Cone Penetrometer (DCP). DCP analysis consists of driving an approximately 1-inch diameter steel rod into the ground utilizing a 35=pound drop hammer. By measuring the number of blows it takes to drive the rod every four inches (10 cm), the general density of granular soils and the stiffness of cohesive soils can be determined. The number of blows for each. -increment -can be correlated .to..standard N values typically obtained from Standard Penetration Testing (SPT) performed using a mechanized soil drill rig. DCP-1 and DCP-2 were advanced in the area near the existing east -west trending timber bulkhead. DCP-3 and DCP-4 were advanced into the slope above the existing timber bulkhead. Results from the DCP tests show the .consistency of the subsurface soils is highly variable with depth. Within the upper 10 feet of.the subsurface, the consistency of the soils ranged from soft to very stiff. Subsurface soils near the existing retaining wall (results from DCP-1 and DCP-2) show the upper 2 feet of soil have the least amount of resistance and softest consistency. Soils below 2 feet generally exhibited higher resistance with consistencies ranging from medium stiff to very stiff. In the slopes above the existing retaining wall (results from DCP-3 and DCP-4) the subsurface displayed consistencies ranging from medium stiff to stiff. Refusal conditions were encountered at around 11 ft in DCP-1, DCP-2, and DCP-4. More detailed logs of the subsurface conditions encountered within in our explorations are presented in the Test Pit logs attached at the end of this report. General Geologic Conditions Geologic information for the project site was obtained from the Geologic Map of the Everett 7.5- Minute Quadrangle, Snohomish County, Washington (Minard, 1985) published by the U.S. Geological Survey. This map indicates that the project site is underlain by advance outwash (map 4