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HomeMy WebLinkAboutRS_21_GE Cedar River Levee Settlement Boeing Lines Report_210224_v1 1101 Fawcett Avenue, Suite 200 Tacoma, Washington 98402 253.383.4940 February 24, 2021 Tetra Tech, Inc. 1420 5th Avenue, Suite 650 Seattle, Washington 98101 Attention: Chuck Purnell Subject: Letter Report Levee Embankment Settlement Analysis Cedar River 205 Levee Renton, Washington File No. 0693-078-01 INTRODUCTION This report provides a summary of our settlement analysis for the expanded levee embankment located on the left bank, downstream (northwest) of the Logan Avenue bridge in Renton, Washington. Our services are being provided in accordance with our agreement dated February 2016 and latest amendment dated July 30, 2019. More information on the overall project and is included in our Levee Stability and Certification report issued as a draft dated November 17, 2017. The settlement analysis provided in the November 2017 report was intended to provide a rough estimate of long-term settlement that could occur over the life of the project. We also provided a letter dated September 17, 2018 that clarified the amount of settlement that was predicted as a direct result of fill placed as part of the proposed levee improvements. Both analyses were simple and conservative. They included combining the highest compressibility soil profiles identified on the project with the largest embankment loads. The settlement analyses presented in this report are intended to help quantify the risk of differential and total settlement that could affect a waterline owned and operated by Boeing, that passes through the project area and under the proposed levee fill prism. This analysis is bases on a specific loading case at a specific location. Accordingly, results of this more complex and focused analysis might not match our previous analyses. PROPOSED LEVEE CONSTRUCTION AND SITE CONSTRAINTS The proposed levee modifications are intended to resolve a deficiency identified in the levee system from previous analyses. An approximate 120-foot length of levee located on the right bank of the river downstream (northwest) of the Logan Avenue bridge does not meet levee standards for height (freeboard) or minimum standard widths. Cedar River 205 Levee | February 24, 2021 Page 2 File No. 0693-078-01 Levee modifications in this area will include adding fill to the existing levee to raise the crest and widen it. The area is constrained by a roadway, E Perimeter Road, located directly on the landside toe of the levee. Construction of a levee section, as proposed on the original construction of the Cedar River Levee, is not practical without encroaching on the roadway. A mechanically stabilized earth (MSE) wall, also known as, a structural earth wall (SEW) will be used to support the embankment fill and will form a portion of the levee embankment. The construction will include raising grade by placement of up to about 5 feet of fill. A significant portion of this fill will be placed directly over the top of two 12-inch waterlines that are located about 3 to 5 feet below current grade. Preliminary plans, including approximate location of the existing waterlines, is shown in Figure 1. DESIGN SUBSURFACE CONDITIONS AND SETTLEMENT ANALYSIS We evaluated settlement in this location using two design soil profiles. The first design soil profile was based on the one subsurface exploration within this specific location. This exploration, PA-100, was advanced by USACE as part of the original levee design study in 1999. The approximate location of this exploration is shown in Figure 1, Vicinity Map. This exploration indicates a typical alluvial profile of sands and silts. No indications of organics were noted except for a note in one sample that indicated minor wood debris. Laboratory analysis from this boring was not provided. We assumed compression indices (Cce) based on laboratory work from explorations elsewhere on the project with similar soil types. This profile was developed to provide our best estimate of the settlement. The second design profile is based on an extreme case assuming there could be a significant amount of highly compressible soils including highly organic soils. These types of soils are known to be present in Renton south of Lake Washington. However, there is not any indication that this degree of compressible organic material is present in this location. This profile was developed to provide an upper estimate of settlement that is very unlikely to be exceeded. We evaluated the predicted settlement of the proposed embankment using Settle3 (Rocscience Inc. 2020). Settle3 evaluates the settlement using a computer model of different soil layers with compression properties. The model uses a Boussinesq soil stress distribution to calculate variable surface loads and the resulting initial elastic settlement and primary consolidation settlement. Secondary compression (or creep) was not included in this settlement analysis and is not expected to be a significant contribution to the total settlement. For each design profile we calculated the initial soil stresses due to the existing embankment and soil overburden. We then calculated the increase in soil stress due to the construction of the proposed levee improvements. Our analysis is based only on the settlement induced additional embankment loading that will be applied as part of this project. Figure 2 includes the results of our analysis. This figure shows the predicted settlement for both design soil profiles along a, “Settlement Analysis Centerline,” that is defined in Figure 1. The results presented in Figure 2 show variations of less than a quarter of an inch. This is only to illustrate the variation in the estimated settlement. This should not be taken as an indication of precision. Cedar River 205 Levee | February 24, 2021 Page 3 File No. 0693-078-01 DISCUSSION OF ANALYSIS RESULTS The settlement estimates provided are based on standard soil mechanics theory and established geotechnical engineering methods. Geotechnical engineering, and specifically settlement analysis, is subject to significant uncertainty. This uncertainty stems both from incomplete knowledge of subsurface conditions and the inherent variability of geologic materials. This degree of uncertainty must be understood when evaluating the risks associated with embankment construction. The settlement estimates only indicate differential settlement due to the variation in surface loading. They do not include differential settlement that could occur due to soil v ariation. In our experience differential settlement due to inherent soil variation could induce additional high and low points that could be as much as 50 percent above or 50 percent below the average settlement over a length of about 50 feet. This differential settlement due to natural soil variation within soil units cannot be practically captured in an analysis. Given the relatively small area and the relatively small total or average settlements predicted, it is our opinion that differential settlement caused by soil variation is not likely to be a significant contribution. It is also our opinion that it is highly unlikely that any natural variation in the soil would cause the settlement to exceed the, “Upper Estimate” prediction. Cedar River 205 Levee | February 24, 2021 Page 4 File No. 0693-078-01 LIMITATIONS We have prepared this report for Tetra Tech and the Cedar River 205 project. Tetra Tech may distribute copies of this report to their authorized agents and project partners as may be required for the project. The analyses presented in this report are based on an assumed subsurface profile developed through interpretation of older subsurface investigations and limited laboratory testing. Our services have been provided to assist the team understand and quantify the risks associated with the construction. Geotechnical analyses can provide insight into the expected performance of structures, but cannot guarantee favorable results. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. The conclusions, recommendations, and opinions presented in this report are based on our professional knowledge, judgment and experience. No warranty or other conditions, express or implied, should be understood. Please refer to Appendix A, Report Limitations and Guidelines for Use, for additional information pertaining to use of this report. Sincerely, GeoEngineers, Inc. February 24, 2021 Lyle J. Stone, PE Associate LJS:mls Attachments: Figure 1. Boeing Waterline Crossing Figure 2. Estimated Settlement Induced by Levee Improvements Appendix A. Report Limitations and Guidelines for Use One copy submitted electronically 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 off icial document of record. Data Source: Microsoft Excel 365 Figure 2 Estimated Settlement Induced by Levee Improvements Cedar River 205 Levee Renton, Washington 0693-078-01 Date Exported: 02/24/21 APPENDIX A Report Limitations and Guidelines for Use Cedar River 205 Levee | February 24, 2021 Page A-1 GeoEngineers, Inc. File No. 0693-078-01 APPENDIX A REPORT LIMITATIONS AND GUIDELINES FOR USE1 This appendix provides information to help you manage your risks with respect to the use of this report. Report Use and Reliance This report has been prepared for Tetra Tech and the Cedar River 205 project. GeoEngineers structures its services to meet the specific needs of its clients. No party other than Tetra Tech may rely on the product of our services unless we agree to such reliance in advance and in writing. Within the limitations of the agreed scope of services for the Project, and its schedule and budget, our services have been executed in accordance with our Agreement dated February 2016 and latest amendment dated July 30, 2019 and generally accepted geotechnical practices in this area at the time this report was prepared. We do not authorize, and will not be responsible for, the use of this report for any purposes or Projects other than those identified in this report. If changes to the Project or property occur after the date of this report, GeoEngineers cannot be responsible for any consequences of such changes in relation to this report unless we have been given the opportunity to review our interpretations and recommendations in the context of such changes. Based on that review, we can provide written modifications or confirmation, as appropriate. 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Please confer with GeoEngineers if you need to know how these “Report Limitations and Guidelines for Use” apply to your Project or site. 1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org.