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3753_001.pdfNELSON EOT C ICAL SSOCI ES, C. GEOTECHNICAL ENGINEERS & GEOLOGISTS Main Office 17311 — 135" Ave NE, A-500 Woodinville, WA 98072 (425) 486-1669 - FAX (425) 481-2510 August 21, 2018 Mr. Derek Abbott 221 — 185"' Place SW Bothell, Washington 98012 Construction Monitoring Summary Letter Abbott Residence 16404 — 75" Place West Edmonds, Washington NGA File No. 9175B 16 Dear Mr. Abbott: Engineering -Geology Branch 5526 Industry Lane, #2 East Wenatchee, WA 98802 (509) 665-7696 • FAX (509) 665-7692 This letter summarizes our geotechnical construction monitoring services for the Abbott Residence project located at 16404 — 75"' Place West in Edmonds, Washington. Introduction We were retained to provide part- to full-time monitoring and consultation services during the earthwork phase of construction. Our earthwork monitoring activities at the project took place on a part- to full-time basis from December 14, 2016 through July 13, 2018 and included observing soldier pile wall installation, augercast pier installation, pin pile installation, footing drain installation, and erosion control measures. Our observations and conclusions were documented in Field Reports 1 through 45, all of which have been submitted to you and the City of Edmonds. Site Observations We observed the installation of 21 soldier piles that varied in length between 20 to 40 feet long into 24- inch diameter drilled holes. Some of the holes experienced caving during drilling. When this occurred the holes were cased to facilitate the beam installation. After each hole was drilled, the contractor placed the steel beams into the holes and backfilled the holes with lean mix concrete to the bottom of the lagging elevation. After the steel beams were set, the lagging was installed, which consisted of 4-inch by 12-inch pressure treated timber spanning the spaces between the piles. Lagging was separated by '/4-inch nails throughout the extent of the wall, to facilitate drainage through the lagging elements. Construction Monitoring Summary Letter Abbott Residence Edmonds, Washington NGA File No. 9175B 16 August 21, 2018 Page 2 We then monitored the augercast pier installation activities for the structure foundations. We observed the drilling of 71, 18-inch diameter holes advanced to depths of approximately 25 feet below the residence foundation subgrade throughout the entire residence foundation area. Upon reaching this depth, the auger was withdrawn from the hole while pumping structural concrete into the holes. Rebar cages were installed into the holes after the auger was removed. Based on our observations, it is our opinion that all of the augercast piers were installed in accordance with the approved plans and our recommendations. We also observed the installation of49, 4-inch lain files for the structural slabs. The; lain piles consisted of Schedule 40 galvanized steel piles and were driven between 6.0 and 18.7 feet below the ground surface. The pin piles were driven with a 1,100 TB425BX hammer to a refusal criteria of less than one inch of movement during 15 seconds of continuous driving. Based on our observations, it is our opinion that the pin piles were installed in accordance with the approved plans and our recommendations. We also observed that footing drains were installed along the exterior portions of the residence and garage. The drains consisted of 4-inch perforated pipes. The drains were surrounded with washed rock and covered with filter fabric. We were informed by the contractor that the footing drains and the roof drains were connected to the existing stormwater system along the northern portion of the property. We observed the construction of both cut and reinforced -fill rockeries within the property. The rockery subgrades were overexcavated and replaced with rock spalls. The rockeries were supported directly on the rock spalls and were embedded a minimum of 18-inches below the ground surface. A drainage layer of crushed rock was placed behind the rockery facing. A 4-inch perforated drain was placed behind the rockeries within the upper portion of the site, while a drain pipe was excluded from the very lower rockeries due to not having enough fall to a suitable discharge point. The reinforced fill rockeries were then backfilled with granular pit -run soils. Geo-grid wraps were placed behind the rockery facing and drainage layer extending back a minimum of five feet. We evaluated the backfill with a nuclear densometer and the test results met or exceeded 95% compaction of ASTM D1557. Based on our observations, it is our opinion that the rockeries within the site were suitably constructed in accordance with the approved plans and our recommendations. During construction, we observed that temporary erosion control measures generally consisted of a silt fence and straw bales around the exterior portions of the excavation area along with a rock spall entrance. We did not observe any indications of soil track out within the streets or erosion issues during construction. We visited the site on August 17, 2018 to observe the final landscaping preparation. We observed that all of the bare ground within the site had been covered with bark, grass and plants. It is our opinion that the erosion control methods incorporated into the landscape design appear to be adequate. NELSON GEOTECHNICAL ASSOCIATES, INC. Construction Monitoring Summary Letter Abbott Residence Edmonds, Washington NGA File No. 9175B16 August 21, 2018 Page 3 Conclusion Based on our part-time observations, it is our opinion that the geotechnical earthwork activities at this site, including residential foundation subgrade, shoring wall, pier and pin pile installation, subsurface drainage, and erosion control methods were completed in general accordance with our recommendations, contract plans, and specifications. The site slopes should be closely monitored for any signs of distress. If any distress is observed, we should be contacted immediately to evaluate the conditions and provide recommendations for slope repairs. Also, long-term maintenance of the drains and landscaped areas is important to prevent water from flowing over the site slopes and creating instability concerns. All other recommendations and precautions presented in our report and memo regarding maintaining slope stability should be strictly followed. We recommend that our report and memo along with this letter be passed on to future home owners if the house is sold. NELSON GEOTECHNICAL ASSOCIATES, INC. Construction Monitoring Summary Letter Abbott Residence Edmonds, Washington NGA File No. 9175B16 August 21, 2018 Page 4 We appreciate the opportunity to be of service to you on this project. We consider our services for this project to be complete, unless you specifically contact us for additional work. If you have any questions regarding this letter or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Lee S. Bellah, LG Project Geologist Khaled M. Shawish, PE Principal LSB:KMS:dy NELSON GEOTECHNICAL ASSOCIATES, INC.