1130 RAINIER AVE Geotech Report 2025-07-28

Everett Housing Authority JN 12080 May16, 2012 Page 3 just above the existing grade. Where overexcavations for the building foundations are expected to be approximately 6 feet or less, using conventional footings for the buildings that that are placed on the competent native soil or on structural fill placed over the competent native soil would be a standard foundation option. However, where deeper overexcavations would be needed to reach competent soil, avoiding the overexcavation and using a deep foundation system is likely a more economical system. Because the buildings are not tall and there is little slope at the site, we believe that using driven pipe piles is a very feasible and economical foundation system for this project; additional information regarding the piles is given in a subsequent section of this report. Peat soil was revealed in the test borings in approximately the area of the proposed eastern building and the eastern end of the southwestern building. This soil is highly organic and thus is very compressible. Based on the condition of the lower parking lot, it appears that settlement of the peat soil has been occurring since fill soil was placed over it to construct the parking lot. Settlement of the peat will likely continue in the future; this would thus negatively affect any floor slabs constructed for these buildings. For this reason, unless the peat is removed, the pipe piles should also be used to support slabs of these buildings. If a crawl space system is used, then the piles would just be needed for foundations. Projects involving small-diameter pipe piles often include the need for lateral resistance from fill placed against the foundations. If this is the case for this project, it is important that the structural engineer indicate this requirement on the plans for the general and earthwork contractor's information. Because of the existence of the peat soil on this site, it is likely that some settlement of the ground surrounding pile-supported buildings will occur over time. In order to reduce the potential problems associated with this, we recommend the following: • Fill to the desired site grades several months prior to constructing on-grade slabs, walkways, and pavements around the buildings. This allows the underlying soils to undergo some consolidation under the new soil loads before final grading is accomplished. • Connect all in-ground utilities beneath the floor slabs to the pile-supported floors or grade beams. This is intended to prevent utilities, such as sewers, from being pulled out of the floor as the underlying soils settle away from the slab. Hangers or straps can be poured into the floors and grade beams to carry the piping. The spacing of these supporting elements will depend on the distance that the pipe material can span unsupported. • Construct all entrance walkways as reinforced slabs that are doweled into the grade beam at the door thresholds. This will allow the walkways to ramp down and away from the building as they settle, without causing a downset at the threshold. • Isolate on-grade elements, such as walkways or pavements, from pile-supported foundations and columns to allow differential movement. The drainage and/or waterproofing recommendations presented in this report are intended only to prevent active seepage from flowing through concrete walls or slabs. Even in the absence of active seepage into and beneath structures, water vapor can migrate through walls, slabs, and floors from the surrounding soil, and can even be transmitted from slabs and foundation walls due to the concrete curing process. Water vapor also results from occupant uses, such as cooking and GEOTECH CONSULTANTS,INC.