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Home My WebLink AboutEx15_Secondary_Geotechnical_Engineering_Review 1101 South Fawcett Avenue, Suite 200 Tacoma, Washington 98402 253.383.4940 October 15, 2020 City of Renton Community & Economic Development 1055 South Grady Way Renton, Washington 98057-3232 Attention: Angelea Weihs Subject: Geotechnical Engineering Review VEK on Aberdeen Renton, Washington File No. 0693-089-00 INTRODUCTION This report presents comments from our review of geotechnical engineering analyses of the proposed VEK on Aberdeen development located at 957 Aberdeen Avenue NE in Renton, Washington. Our services are being provided to the City of Renton Department of Community and Economic Development in accordance with our agreement dated September 21, 2020 and executed October 5, 2020. The proposed development will include construction near Sensitive Slopes and a Protected Slope as defined by City of Renton Municipal Code. The project also includes construction of a stormwater pipe proposed within the protected slope that would discharge into stream and wetland buffers. The City has requested a third-party review of the geotechnical report and grading plan to confirm that the analysis and conclusions provided are appropriate before approving the development. We reviewed a geotechnical report prepared for the project by The Riley Group, Inc. (RGI) dated September 2, 2020 addressing slope stability. We also reviewed the preliminary civil plans prepared by Encompass Engineering and Surveying dated May 8, 2020. GEOTECHNICAL REVIEW The following presents our review comments on the report and project preliminary civil plans. Our review only addresses geotechnical aspects of the proposed project. 1. In Section 4.6.6, RGI states, “RGI completed a stability analysis for the currently proposed conditions as shown on the plans and included the proposed drainage facilities.” and indicates modifications that were made to the reviewed plans from a previous version. We suggest that RGI reference a date or other unique indicator of which version of the plans were reviewed and used as a basis of analysis. Alternatively, RGI could provide a review letter or other appropriate confirmation indicating that they have reviewed the final plan set and that it is consistent with their assumptions and recommendations as they recommend in Section 6.0. EXHIBIT 15 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 City of Renton | October 15, 2020 Page 2 File No. 0693-089-00 2. In Appendix B, RGI states “The analyses were performed for the existing conditions under static and seismic loading condition, as well as the proposed conditions.” The existing condition analysis was not provided, and the results of the existing condition analyses were not indicated. These should be provided so the calculated stability of the existing conditions can be compared to the calculated stability of the proposed conditions. This comparison can directly demonstrate that the development meets the criteria of Renton Municipal Code Section 4-3-050F.2.a.ii.(a) “The proposal will not increase the threat of the geological hazard to adjacent or abutting properties beyond pre-development conditions”. This is specifically an issue for Section B-B’ that extends to the adjacent property to the north. 3. The analysis indicates that a horizontal seismic coefficient of 0.2g was applied. It is not clear what seismic design level (i.e., return period) this is based on or if a reduction was included. A seismic event with a 2 percent probability of exceedance in 50 years (about 2,475-year return period in accordance with the International Building Code [IBC]) is typically used to analyze slopes and potential failures that will impact inhabited structures. For a pseudo-static analysis, one-half of the Peak Ground Acceleration (PGA) is typically used based on the assumption that some permanent slope movement is acceptable and not a life safety hazard. CONCLUSIONS It is our opinion that the project can be constructed generally as envisioned without causing undue risk to the public provided that the recommendations in the project geotechnical report are incorporated into the design and followed during construction. In order to confirm that the proposed development meets specific municipal code requirements, we recommend that the City require the analyses described in Comment No. 2 be submitted for additional review and that other comments be addressed. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices for geotechnical engineering in this area at the time this report was prepared. Our services were provided to assist the City of Renton evaluate a geotechnical analysis submitted as part of a permit application. GeoEngineers cannot attest to the accuracy or completeness of the materials provided. The conclusions, recommendations and opinions presented in this report are based on our professional knowledge, judgment, and experience. No warranty, express or implied, applies to the services or this report. If there are any questions or if you wish to discuss any of our review comments, please contact us. Thank you for the opportunity to be of service to the City of Renton. Sincerely, GeoEngineers, Inc. Lyle J. Stone, PE Associate Geotechnical Engineer LJS:leh Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 1101 South Fawcett Avenue, Suite 200 Tacoma, Washington 98402 253.383.4940 October 30, 2020 City of Renton Community & Economic Development 1055 South Grady Way Renton, Washington 98057-3232 Attention: Angelea Weihs Subject: Geotechnical Engineering Review VEK on Aberdeen Renton, Washington File No. 0693-089-00 INTRODUCTION This report presents comments from our review of geotechnical engineering analyses of the proposed VEK on Aberdeen development located at 957 Aberdeen Avenue NE in Renton, Washington. Our services are being provided to the City of Renton Department of Community and Economic Development in accordance with our agreement dated September 21, 2020 and executed October 5, 2020. The proposed development will include construction near Sensitive Slopes and a Protected Slope as defined by City of Renton Municipal Code. The project also includes construction of a stormwater pipe proposed within the protected slope that would discharge into stream and wetland buffers. The City has requested a third-party review of the geotechnical report and grading plan to confirm that the analysis and conclusions provided are appropriate before approving the development. We reviewed a geotechnical report prepared for the project by The Riley Group, Inc. (RGI) dated September 2, 2020 addressing slope stability. We also reviewed the preliminary civil plans prepared by Encompass Engineering and Surveying dated May 8, 2020. We provided our comments on these documents in a letter dated October 15, 2020. GEOTECHNICAL REVIEW We reviewed the document “Response to Draft Comments” prepared by The Riley Group dated October 23, 2020. We have no further comments on this document or previously reviewed documents. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 City of Renton | October 30, 2020 Page 2 File No. 0693-089-00 CONCLUSIONS It is our opinion that the project can be constructed generally as envisioned without causing undue risk to the public provided that the recommendations in the project geotechnical report are incorporated into the design and followed during construction. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices for geotechnical engineering in this area at the time this report was prepared. Our services were provided to assist the City of Renton evaluate a geotechnical analysis submitted as part of a permit application. GeoEngineers cannot attest to the accuracy or completeness of the materials provided. The conclusions, recommendations and opinions presented in this report are based on our professional knowledge, judgment, and experience. No warranty, express or implied, applies to the services or this report. If there are any questions or if you wish to discuss any of our review comments, please contact us. Thank you for the opportunity to be of service to the City of Renton. Sincerely, GeoEngineers, Inc. Lyle J. Stone, PE Associate Geotechnical Engineer 10/30/2020 LJS:tt Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2