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1 <br /> August 2, 2021 lerracon <br /> I <br /> BHC Consultants <br /> 1601 5th Avenue, Suite 500 <br /> Seattle, Washington 98101-3604 111 <br /> Attn: Mr. John Gillespie— Project Engineer <br /> P: (206) 357-9914 <br /> E: john.gillespie@bhcconsultants.com <br /> Re: Geotechnical Engineering Report Addendum I <br /> Micropile Foundations— Evergreen Way Pump Station <br /> 6107 Evergreen Way <br /> Everett, Washington <br /> Terracon Project No. 81195189 <br /> Dear Mr. Gillespie: <br /> Terracon Consultants, Inc. (Terracon) has completed Geotechnical Engineering services in general I <br /> accordance with our Subconsultant Services Agreement dated June 23, 2020. We have prepared this <br /> letter to present recommendations for design and construction of micropile foundation elements as <br /> described herein. This letter is intended to be an addendum to the project geotechnical engineering report 1 <br /> titled "City of Everett- Evergreen Way Pump Station Switchgear Building" dated June 8, 2021 and should <br /> be read in conjunction with the referenced report. <br /> During discussion with the design team, Terracon recommended additional subsurface exploration to <br /> confirm subsurface conditions within the anticipated depth of the proposed micropile foundations. We I <br /> understand that BHC and the City of Everett desire to design and construct micropile foundations without <br /> additional subsurface investigation. Subsurface information collected for our June 8, 2020 report <br /> indicates advance glacial outwash soil from bottom of pile cap elevation to a depth of approximately 8% I <br /> feet below the anticipated bottom of pile cap elevation. In our opinion,the risk of encountering unexpected <br /> and adverse subsurface conditions during construction of micropile foundations is somewhat low since <br /> glacially consolidated soil extends below the depth of exploration. I <br /> MICROPILE DESIGN RECOMMENDATIONS11 <br /> Micropiles are being evaluated by the design team to provide uplift resistance to existing pump station <br /> building shallow foundations.We recommend that the micropiles be drilled into the native advance glacial <br /> outwash soil encountered at the project site. We recommend that the micropiles have a minimum length <br /> of 10 feet extending below the pile cap. Micropiles should be designed in both axial compression and i <br /> tension (uplift)using an ultimate (nominal) bond stress of 27 pounds per square inch for pressure grouted <br /> micropiles within the glacially consolidated granular soils. Soil to grout bond capacity should be neglected <br /> for the first 2 feet extending below the pile cap elevation. The ultimate bond stress should be reduced by 1 <br /> Terracon Consultants, Inc. 21905 64th Ave. W, Suite 100 Mountlake Terrace, WA 98043 <br /> P (425) 771 3304 F (425) 771 3549 terracon.com <br /> Environmental CI Facilities ri Geotechnical Ej Materials <br />