11229 19TH AVE SE SILVER LAKE TOWNHOMES WHOLE SITE Geotech Report 2022-10-25

Geotechnical Report Proposed Development: 11229 - 19th Avenue SE, Everett, WA September 16, 2016 Footing Subgrade Preparation:Footing subgrades should be in a dense and stable condition prior to setting forms and placing reinforcing steel. Any loose or softened soil should be removed from the footing excavations. The adequacy of the footing subgrade soils should be verified by a representative of PanGEO, prior to placing forms or rebar. 5.2.2 Pipe Pile Foundations As previously indicated, in-lieu of over-excavation and backfill, alternatively,pin pile foundations may be used to support Building E. The following sections present our design recommendations for pin pile foundations. Pin Pile Sizes - In our opinion, 3- or 4-inch diameter, Schedule 40, galvanized, steel pipes (pin piles) may be used to support Building E as an alternative to foundation soil over-excavation. Three and four-inch diameter pin piles are typically installed using small hammers mounted on a small excavator. Pin Pile Capacity - The number of piles required depends on the magnitude of the design load, and should be determined by the project structural engineer. Allowable axial compression capacities of 6 and 10 tons may be used for the 3- and 4-inch diameter pin piles,respectively, with an approximate factor of safety of 2. Penetration resistance required to achieve the capacities will be determined based on the hammer used to install the pile. Tensile capacity of pin piles should be ignored in design calculations. It is our experience that the driven pipe pile foundations should provide adequate support with total settlements on the order of 1/2-inch or less. Pile splices may be made with compression fitted sleeve pipe couplers(see Typical Splicing Detail on page 9). Splicing using welding of pipe joints should not be used, as welds will typically be broken during driving. Three-and four-inch diameter piles are typically installed using small(approximately 850 to 2,000 pound) hammers mounted to a small excavator. The criterion for driving refusal is defined as the minimum amount of time (in seconds) required to achieve one inch of penetration, and it varies with the size of hammer used for pile driving. For 3- and 4-inch pin piles, the Table 2 on page 8 is a summary of driving refusal criteria for different hammer sizes that are commonly used: 16-210 11229 19th Ave SE Rpt Page 7 PanGEO, Inc.