4702 W GLENHAVEN DR 2020-06-16 - Laserfiche WebLink

Oskar Property Deck Limited CAO,Everett,WA Materials Testing&Consulting,Inc. July 17,2019 19B182 Site Investigation Methodology: On June 7, 2019, an MTC Staff Geologist visited the site to perform visual reconnaissance of surface and topographic features of the site upland and adjacent slope, and to conduct targeted subsurface exploration at the proposed foundation area for geologic hazard assessment and site characterization. Salient slope features and existing vegetation were documented to assess general site stability and observe signs of local upland instability in the vicinity of the proposed improvements, including those of an erosional or subsurface nature currently or in the past. MTC advanced three (3) Wildcat Dynamic Cone Penetrometer (DCP) tests at representative locations among the proposed deck foundation area. DCP-1 was advanced near the proposed northern footing of the deck, approximately 20 feet south of the slope crest. DCP-2 was advanced at the proposed western footing, approximately 40 feet from the slope crest. DCP-3 was advanced near the slope crest immediately north of DCP-1 for comparison. All DCP tests were terminated due to practical refusal on dense or hard conditions. Refusal depths ranged from about 4.7 to 10.3 feet below present grade (BPG), generally increasing toward the slope crest. During penetrometer advancement, blow counts were recorded in 10-centimeter increments as a thirty-five-pound weight was dropped a distance of 15 inches. Blow counts were then converted to resistance (kg/cm2), standard penetration blow counts (N-values), and corresponding soil consistency,with complete results shown on the attached logs. MTC also conducted subsurface exploration via one (1) hand auger boring for correlation of blow count data with soil type and to observe groundwater conditions. Hand auger HA-1 was advance between DCP-1 and DCP-2 along the northwest edge of the proposed deck area. Practical refusal was found on obstructions at relatively shallow levels, at about 3.5 feet BPG, due to hand-equipment capabilities. During advancement, we examined and classified materials encountered in accordance with the Unified Soil Classification System (USCS) and recorded pertinent information as possible including soil depths, stratigraphy, soil engineering characteristics, and groundwater occurrence. Upon completion, boring holes were backfilled with existing soil tailings. We reviewed the findings of our prior site explorations (letter dated July 31, 2017) which focused on previous deck improvements at the northeast end of the site (area on Figure 2). Relevant results utilized for assessment of the current project area in the northwest part of the site are appended to this report. A project location and vicinity map is shown in Figure 1, Appendix A. An aerial photo of site and bordering slope conditions with exploration locations is shown in Figure 2. In Figure 3 is a site plan of the proposed deck addition area overlain with test locations. Photos showing representative site and slope features are provided in Appendix B. Complete results of DCP tests and hand auger borings are presented as logs in Appendix C,with a USCS soil classification chart provided for reference in Figure 4. 2 .,9(4