4849 SPIRE LN 2023 Geotech Report 2025-10-15

Proposed Remedial Excavation: 4849 Spire Lane, Everett, WA December 8.2022 underpinning the section of the soutli foundation wall adjacent to the proposed excavation. The underpinning should also extend past the limits of the excavation by at feast 5 feet. In our opinion, small diameter driven steel pipe piles represent a feasible foundation underpinning option in terms of cost and long -terns performance. Shall diameter driven steel pipe piles may be utilized to support the structure by transferring the foundation loads to the underlying dense to very dense soils. Pipe piles of 2 to 4 inches in diameter are typically utilized for this purpose. 2-inch pin piles are typically installed using portable, liandheld equipment and are suited for areas where limited site access exists or in low headroom areas. 3-inch and 4-inch pin piles are typically installed using small hammers mounted on a small to medium-sized excavator. Pin Pile Size — Because the piles will need to be installed directly adjacent or under the existing building footing, and because foundation loads are anticipated to be relatively low, we anticipate that 2-inch diameter pin piles would be used for this project. Pin Pile Capacity - The number- of piles required depends on the magnitude of the design load and the capacity of the existing footing to span between the piles. 2-inch diameter pin piles are typically installed with a 90-lb jackhammer with the operator leaning heavily on the hammer during driving, or a 140-lb jackhammer (often referred to as a "rhino' hammer). We recommend that an allowable axial compression capacity of 3 tons per pile be utilized for design, with an approximate factor of safety of 2.0 when piles are driven to practical refusal (less than I inch of penetration for 1 minute of continuous driving). 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/Z-inch or less. Pin Pile Specifications - We recommend that the following specifications be included on the project plans: 1. 2-inch diameter piles should consist of Schedule-80, ASTM A-53 Grade "A" pipe. 2. 2-inch piles shall be driven to refusal with a 140-lb jackhammer or a 90-lb hammer with the operator leaning heavily on the liammer during driving. Refusal is defined as no more than 1 inch of penetration for I minute of continuous driving. 22-389_4849 spire lane evereUrpt.doex Page 6 PanGEO, Inc.