6200 12TH DR SE 2020-10-22 - Laserfiche WebLink

G10T13C11 240110th Ave S CONSULTANT'S, INC. Soattte,Wa(425)74 98-5 02 18 • (425)747-5G1S June 25, 2019 JN 16298 Catholic Housing Services of Western Washington vie 7-0 `�JN2-- 100-23rd Avenue South Seattle, Washington 98144 Attention: Michelle Umadhay via email: MichelleU@ccsww,org Subject: Final Letter- Geotechnical Engineering Observations Everett Safe Streets Supportive Housing Project 6200— 12th Drive Southeast Everett, Washington Greetings: Our personnel were onsite numerous days between May 2018 and November 2018 to perform geotechnical engineering testing and observation services for the subject project. Our services were essentially done for the two major structures for the project: the building and detention vault. A summary of our services is discussed below. The initial work that our personnel was onsite for was the installation of 6-inch-diameter steel piles needed for the building foundation.These piles were installed in May 2018 by Pile King using a 3000- pound hydraulic jackhammer to a refusal rate of 6 seconds per inch or slower. In total, 151 piles were installed,with embedment depths ranging from approximately 26 to 40 feet; longer piles were installed on the western side of the building as anticipated. In our opinion, based on our observations and the refusal rates obtained, the 151 piles were adequately installed to the design capacity of 20 tons. We returned to the site in October 2018 when the detention vault for the project was installed on the eastern portion of the site. We initially observed the soil conditions in the base of the vault. In a large portion of the vault area, competent, dense native soils were revealed at the base of the vault. However, at the northwestern portion, the competent soil was not revealed for up to about 5 feet below the base of the vault. In this northwestern portion, following the excavation down to competent soil, imported quarry spalls were used as structural fill between the competent soil and the base of the vault. Prior to the placement of the base of the vault, we observed that the base consisted of either competent native soil or the imported quarry spalls; the base conditions were suitable for the design bearing capacity of 3,000 psf. In November 2018,following the placement of the vault, our personnel were onsite to perform density testing on backfill soils placed around the outside of the vault. The backfill soils generally consisted of onsite soil and/or imported pit-run that was compacted with vibratory equipment. Our personnel periodically observed and tested the backfill soil for this work, and the backfill soil was found to be adequately compacted;verification of 95 percent compaction with a nuclear densometer was used to confirm adequate compaction.