4920 EVERGREEN WAY STAPLES Geotech Report 2022-10-25

Geotechnical Engineering Report IIrracon Staples Rockery Failure Everett,Washington March 8, 2019 Terracon Project No. 81175122 Approximate Depth to Stratum Bottom of Stratum Material Description Consistency/ (feet) Density 1. Boring B-1 was terminated at its planned depth within this stratum. Split-spoon sampler refusal occurred at sampling intervals for 45 and 55 feet bgs. Subsurface conditions encountered at the boring location are assumed to be reasonably consistent in the immediate vicinity of the project location. Details of the boring can be found in Appendix A of this report. Laboratory tests consisted of index testing conducted on selected soil samples to verify the USCS visual classifications. Test results are presented in Appendix B. 3.3 Groundwater Groundwater was not observed in the soil boring at the time of the exploration. Changes in soil moisture that would indicate the presence of groundwater were not observed. Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the explorations were performed. In addition, perched water can develop over low-permeability soil. 3.4 Rockery Failure The section of failed rockery was first observed by Terracon on December 1, 2017. We understand that indications of ground subsidence and movement were first observed in the preceding one to two weeks prior to our site visit. Subsequent site visits were performed on December 6 and 21, 2017 for further study. Pictures taken at the time of the investigation of the ground surface at the collapsed section of rockery are included in Appendix A. The immediate area of the rockery failure demonstrates two surface expressions indicating wall movements: headscarp and subsidence. Headscarp: vertical displacement corresponding to a collapsed section of the rockery. Dimensions of the headscarp are approximately 20 feet long and 5 feet wide. The northernmost extent of the headscarp is about 50 feet from the north end of the building. This section of failed rockery is presenting an immediate risk to the building. Subsidence: ground settlement or slumping resulting in an area of depression indicates movement of the rockery, but it is uncertain if a collapsed condition has occurred. The area of subsidence is approximately 55 feet long and about 6 feet wide. The northernmost extent of the subsidence area is about 45 feet from the north end of the building. This section of failed rockery is unstable and may collapse at any time posing an immediate risk to the building. Responsive • Resourceful • Reliable 4