3400 RIVERFRONT BLVD Geotech Report 2022-10-25 (2)

GEoDESIGW Memorandum Page 1 To: Nick Abdelnour From: Ryan T. Lawrence, P.E. (Oregon) and Scott V. Mills, P.E. Company: Polygon Northwest Company Date: September 21, 2015 Address: 11624 SE 5th Street, Suite 100 Bellevue, WA 98005 cc: n/a GDI Project: Polygon-127-01 RE: Everett Riverfront Simpson Plat Everett, Washington Evaluation of Settlement Data GeoDesign, Inc. previously prepared a geotechnical report that presented our conclusions and recommendations for this project'. As recommended in our report, Polygon placed an approximately 10-foot-high surcharge on the northern portion of the site, which was designated as the Phase 1 area. Once the underlying soil in the Phase 1 area has adequately consolidated from the surcharge load, Polygon will move the surcharge to the Phase 2 and Phase 3 areas. The Surcharge Plan presented in Attachment A shows the Phase 1 area where the surcharge is currently located. We have been performing settlement monitoring to evaluate the rate and magnitude of settlement resulting from the placement of the surcharge in the Phase 1 area. There are currently ten settlement plates and two vibrating wire piezometers that we are collecting data from in the Phase 1 area. Plots of the data we have collected in the Phase 1 area are presented in Attachment B. As shown in the settlement plate plots in Attachment B, the rate of settlement has slowed considerably since the surcharge was initially placed. It appears that the surcharge has been left in place long enough that primary consolidation of the underlying soil has finished or is nearly finished. The magnitude of settlement from the surcharge placement generally ranges from 0.8 to 1.3 feet. The plots of the vibrating wire piezometers show that most of the excess pore water pressure that developed when the surcharge was initially placed has dissipated, which is also an indication that primary consolidation is nearly complete. We note that standing water from recent rainfall at the site has accumulated around vibrating wire piezometer 1, which is likely resulting in the data showing a slight pressure increase that is obscuring the actual magnitude of pressure dissipation. Although it is not the goal of the surcharge program to complete primary consolidation of the underlying soil, it is our opinion that if primary consolidation is achieved (or nearly achieved) under surcharge loading, it is reasonable to expect that minimal additional settlement will occur from the much smaller development loads that will occur after the surcharge has been removed. 'GeoDesign,Inc. Report of Geotechnical Engineering Services;Everett Riverfront Simpson Plat;Everett, Washington,dated August 12,2015. GeoDesign Project: Polygon-127-01 15575 SW Sequoia Pkwy-Suite 100 I Portland OR 97224 I Off 503.968.8787 I Fax 503.968.3068