1215 W MUKILTEO BLVD 2017-07-28 - Laserfiche WebLink

April 29,2015 HWA Project No.2014-162-21 (horizontal : vertical) batter. The lower rockery wall measures approximately 9 feet tall at its maximum height and is constructed at a 1H : 3V batter. The lower rockery wall is founded at the top of a 4 foot tall cast in place concrete retaining wall. The rocks comprising the existing upper and lower rockeries showed evidence of significant deterioration that is most likely a result of chemical and mechanical weathering of the rocks. The cast in place concrete wall at the base of the slope appeared to be in good condition with no signs of distress or deformation. HWA Soil Explorations On October 17, 2014, HWA representatives visited the site and performed a subsurface investigation including three hand borings, designated HH-1 through HH-3. The hand borings were advanced to depths ranging from 3.6 to 5.6 feet below ground surface (bgs). Dynamic cone penetration (DCP) tests, were completed at all hand boring locations, to explore the relative density of near-surface soils. Each hand boring and associated DCP test was advanced and logged by an HWA geotechnical engineer, using hand excavation tools. DCP testing equipment consists of a steel extension shaft assembly, with a 60 degree hardened steel cone tip attached to one end, which is driven into the subsoil by means of a sliding drop hammer. The base diameter of the cone is 20 mm (0.79 inches). The diameter of the shaft is 8 mm (0.315 inches) less than the cone, to reduce rod friction at shallow penetration depths. The DCP is driven by repeatedly dropping an 8-kg (17.6-pound) sliding hammer from a fixed height of 575 mm (22.6 inches). The depth of cone penetration is measured after each hammer drop and the in-situ shear strength of the soil is reported in terms of the DCP index. The DCP index is based on the average penetration depth resulting from 1 blow of the 8-kg (17.6-pound) hammer and is reported as millimeters per blow (mm/blow). The data obtained from the DCP tests was then correlated to Standard Penetration Test (SPT) values, in order to evaluate the strength of the subgrade soils for use in evaluating the allowable bearing capacity of the site soils. The DCP data, converted to SPT, is plotted on the hand boring logs in Appendix A. The locations of the hand borings were determined in the field by taping distances from surveyed site features. The approximate locations of each hand boring and DCP test is indicated in the Site and Exploration Plan, Figure 2. Exploration logs of the hand borings and DCP tests are shown in Figures A-2 through A-4. A legend of the terms and symbols used on the exploration logs is included on Figure A-1. General Geologic Conditions Geologic information for the project area was obtained from the Preliminary Surficial Geologic Map of the Mukilteo and Everett Quadrangles, Snohomish County Washington (Smith, 1976). Based on the geologic map of the area, the site is underlain by Whidbey Formation soils 2014-162 Letter Report 2 HWA GEOSCIENCES INC.