2320 RAILWAY AVE INTERWEST CONSTRUCTION INC Geotech Report 2023-02-17

Interwest Construction Co.-Railway Avenue Improvements,Everett,WA Feb. 14,2019/Revised Feb. 7,2020 Geotechnical Engineering Report P1486-T18 1 Subgrade Observation and Compaction Testing: Regardless of material or location,all structural fill should be placed over firm,unyielding subgrades prepared in accordance with the Site Preparation ' section of this report. The condition of all subgrades should be observed by geotechnical personnel before filling or construction begins. Also, fill soil compaction should be verified by means of in-place density tests performed during fill placement so that adequacy of soil compaction efforts may be evaluated as earthwork progresses. Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on their grain-size distribution and moisture content when they are placed. As the"fines"content(that soil fraction passing the U.S.No.200 Sieve)increases,soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than 2 percentage points above or below optimum. For fill placement during wet-weather site work,we recommend using"clean"fill, which refers to soils that have a fines content of 5 percent or less(by weight)based on the soil fraction passing the U.S. No. 4 Sieve. 4.5 Vibrations Planned developments along the proposed Railway Avenue extension include new subsurface utilities along the roadway and a concrete recycling facility. Vibrations transmitted through soil media are rapidly attenuated,while vibrations transmitted through the air(such as those associated with train activity in the railroad right-of-way)might be perceivable but are typically not harmful to people or property. The Bureau of Mines guidelines indicate that the lowest peak particle velocity of possible concern is 2.0 in/sec and that damage does not occur until 5.0 in/sec. We do not anticipate that vibrations from equipment or vehicles associated with the proposed development will have an adverse impact upon the residential properties located to the north,south and west of the project site. 5.0 RECOMMENDED ADDITIONAL SERVICES Because the future performance and integrity of the structural elements will depend largely on proper site preparation, drainage, fill placement, and construction procedures, monitoring and testing by experienced geotechnical personnel should be considered an integral part of the ' construction process. Subsequently,we recommend that MGI be retained to provide the following post-report services: ' • Review all construction plans and specifications to verify that our design criteria presented in this report have been properly integrated into the design; • Prepare a letter summarizing all review comments (if required); and • Prepare a post-construction letter summarizing all field observations, inspections, and test results (if required). Migizi Group, Inc. Page 12 of 13