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HomeMy WebLinkAboutRS_Geotech_Wall_Maintenace_Letter_230922_v115365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 • (425) 449-4704 • FAX (425) 449-4711 Earth Solutions NW LLC Geotechnical Engineering, Construction Observation/Testing and Environmental Services September 22, 2023 ES-7945.04 Century Communities 20000 North Creek Parkway, Suite 201 Bothell, Washington 98011 Attention: Stacia Bloom Subject: Geotechnical Summary and Wall Maintenance Recommendations Canopy Plat Retaining Walls Renton, Washington Dear Stacia: As requested, Earth Solutions NW, LLC (ESNW) has prepared this letter and final report summarizing the recently completed retaining wall construction at the subject site. Redi-Rock retaining walls are the predominant wall type constructed as part of the residential plat development. Gravity type wall construction and mechanically stabilized earth wall structures were both utilized for the project. The photograph below depicts one of the completed Redi-Rock walls. It should be noted that the offset alignment along the top of the wall provides a series of openings that will accommodate future landscaping elements. Typical Redi-Rock Wall With Landscaping Feature Century Communities ES-7945.04 September 22, 2023 Page 2 Earth Solutions NW, LLC Wall construction for the project also incorporated the use of rockeries. Given the grading requirement at each rockery location, the rockery structures were positioned against a competent native cut face. A typical rockery structure completed for the project is depicted below. Typical Rockey Structure Geotechnical Summary During the course of the site development activities, the undersigned engineer and his field staff observed and documented the rockery and Redi-Rock wall construction. The supporting wall subgrade and related keyway excavations for each wall was observed and tested by our staff during construction. Subsequent installation of the wall drain and associated clean rock drainage layer for each wall was also observed and documented by our field representatives. During the overall wall construction activities, field staff were onsite to further document and test wall backfill and compaction efforts. On this basis, and given the observed and documented wall construction activities, it is the opinion of the undersigned geotechnical engineer that the site retaining wall construction was completed in accordance with our geotechnical recommendations and the approved plans. It should be noted that soldier pile wall construction was also completed along the margins of Lots 43 to 47. The undersigned engineer prepared the design for the soldier pile wall and engaged his field staff to observe and document the construction. Based on the documented construction, combined with observations completed by the engineer during construction, it is the professional opinion of the undersigned engineer that the soldier pile wall was constructed in accordance with the approved plans. Century Communities ES-7945.04 September 22, 2023 Page 3 Earth Solutions NW, LLC Retaining Wall Long Term Maintenance Recommendations Retaining wall construction for residential land development is used to facilitate grading and stability of the completed homesites. Specifically, retaining walls are utilized to reduce the probability of instability resulting from the required grading necessary to establish the project homesites, yard areas, streets and associated infrastructure improvements. The developer, engineer and contractor complete the design and construction of the retaining walls on the basis of the identified site geologic condition and subsequent engineering studies. Once construction is completed, ownership of the retaining walls transfers to the project HOA and individual homeowners (as applicable). Given this transfer of ownership, maintenance of the retaining wall structures also becomes the responsibility of the HOA and/or homeowner. Such maintenance is necessary to ensure good long-term performance of the wall structures. On this basis, the following is a list of recommended “DO’S” and “DON’TS” with respect to retaining wall long- term maintenance. Retaining Wall Maintenance - “DO’S” 1. Check roof drains, gutters and downspouts to be sure they are clear and functioning properly. Without properly functioning gutters and downspouts, stormwater can flow uncontrolled across the property potentially impacting the site retaining wall structures. 2. Clear drainage conveyance systems (i.e. yard drains, etc.) and check them frequently during the rainy season. Be sure the drainage and conveyance systems are functioning properly such that water is prevented from flowing over the top of the wall causing erosion or potential stability problems. 3. Be sure all wall drain outlets are open and clear of debris, vegetation and other material that could block them in a storm. If blockage is evident, have it cleared. 4. Check for noticeable signs of instability (cracks) or changes in wall alignment or movement. Contact a professional civil engineer if wall movement or instability are suspected. 5. Limit watering during the rainy season when little irrigation is required. Prolonged over- saturation of the ground above or below the wall structures may increase the potential for instability. 6. Exercise ordinary common sense with respect to retaining wall maintenance. The homesite and associated retaining wall structures were constructed to meet standards which should protect against most natural occurrences, provided maintenance measures as described above are followed. Century Communities ES-7945.04 September 22, 2023 Page 4 Earth Solutions NW, LLC Retaining Wall Maintenance - “DON’TS” 1.Don’t alter lot grading (particularly above or below wall structures) without competent advice from an engineer. The retaining wall structures have been designed to maintain support of the final grade approved at the time of wall completion. Any subsequent alteration of the grade above or below the retaining wall could compromise the performance and overall stability of the wall structure. 2. Don’t block or alter drainage and related conveyances associated with the retaining wall drainage system(s). Water backed up in surface drains could overflow and introduce unintended water and related hydrostatic pressures to the wall structure. We trust this final report and recommended measures for retaining wall maintenance meet your current needs. If you have questions, or if additional information is required, please call. Sincerely, EARTH SOLUTIONS NW, LLC Raymond A. Coglas, P.E. Senior Principal Engineer cc: Goodfellow Bros. Attention: Kyle Williams 09/22/2023