4920 EVERGREEN WAY STAPLES Geotech Report 2022-10-25

Geotechnical Engineering Report lierracon Staples Rockery Failure■ Everett,Washington March 8, 2019■ Terracon Project No. 81175122 Field Exploration Description A geotechnical exploration program has been performed atop the existing rockery to investigate the recent rockery failure that occurred between Glacier Lane and the west side of the building at 4920 Evergreen Way(i.e. the Staples building), atop the existing rockery. The boring was drilled to 56 1/2 feet below ground surface (bgs). The exploration location was laid out by Terracon personnel. Distances from these locations to the reference features indicated on the attached diagram are approximate. The ground surface elevations at the exploration locations were approximated using Google Earth Imagery, 2017. The GPS coordinates were estimated using field measurements from landmarks identifiable from Google Earth Imagery. The location and elevation reported should be considered accurate only to the degree implied by the means and methods used to define them. A field log of the exploration was prepared by the field engineer on site. The log includes visual classifications of the materials encountered during drilling as well as the engineer's interpretation of the subsurface conditions between samples. The final boring log included with this report represents an interpretation of the field log and includes modifications based on laboratory observation and tests of the samples obtained in the field. The enclosed boring log indicates the vertical sequence of soil and materials encountered during the exploration. Where a soil contact was observed to be gradational, our logs indicate the average contact depth. The samples were classified in the laboratory based on visual observation, texture and plasticity. The descriptions of the soil indicated on the exploration logs are in general accordance with the enclosed General Notes and the Unified Soil Classification System. Estimated group symbols according to the Unified Soil Classification System are given on the exploration logs. A brief description of this classification system is attached to this report. The boring was drilled with a track-mounted rotary drill rig using hollow-stem augers to advance the boreholes. Representative soil samples were obtained by the split-barrel sampling procedure. In the split-barrel sampling procedure, the number of blows required to advance a standard 2- inch O.D. split-barrel sampler the last 12 inches of the typical total 18-inch penetration by means of a 140-pound hammer with a free fall of 30 inches, is the standard penetration resistance value (N). This value is used to estimate the in-situ relative density. The sampling depths, penetration distance, and standard penetration resistance values are shown on the boring logs. The samples were sealed and taken to the laboratory for testing. An automatic SPT hammer was used to advance the split-barrel sampler in the borings performed.An energy transfer ratio(ETR)of 87 percent was reported by the drilling subcontractor for the rig's autohammer. Published correlations between the SPT values and soil properties are based on the lower efficiency cathead and rope method which generates an ETR of about 60 percent efficiency, the consensus ETR value amongst the geotechnical industry. The effect of the automatic hammer's efficiency has been considered in the interpretation and analysis of the subsurface information for this report. Responsive■ Resourceful • Reliable Exhibit A-3