1020 NORTH PARK DR 2022-02-23 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No. 961916 Mason Residence Addition and Deck August 24,2016 Everett,Washington Page 12 'Ls For 2-inch diameter pipe piles driven to refusal using a hand-held, 140-pound jackhammer, we recommend a design axial compression capacity of two tons for each pile. The refusal criterion for this pile and hammer size is defined as less than one inch of movement during 60 seconds of continuous driving. We recommend using galvanized extra strong(Schedule 80)steel pipe. Final pile depths should be expected to vary somewhat and will depend on the depth of the loose material, the nature of the underlying competent soils, and groundwater conditions. The pin piles should penetrate a minimum of five feet into the competent native glacial soils below the fill material in order to develop the design capacity. Based on our explorations, we would recommend that the piles be driven to a minimum depth of 20 feet below the ground surface nearest to the steep slope area and 15 feet within the upper southern portion of the deck to achieve the minimum embedment depth into the competent glacial soils. Piles that do not meet this minimum embedment criterion should be rejected, and replacement piles should be driven after consulting with the structural engineer regarding the new pile locations. The piles should be spaced a minimum of three feet apart to avoid a grouping effect on the piles. Due to the relatively small slenderness ratio of pin piles, maintaining pin pile confinement and lateral support is essential in preventing pile buckling. Pin piles should be suitably embedded into the reinforced concrete. The structural engineer should design the connections of the piles to the foundations. Vertically driven pin piles do not provide meaningful lateral capacity. All lateral loads should be transferred back to the existing residence via grade beams. We also recommend that the deck posts be supported on a series of grade beams that is also tied back into the existing residence. Due to the rigid pile support, friction between the foundation and subgrade soil should not be considered as resisting lateral pressures on this structure. Slab-on-Grade If a slab-on-grade is planned for this site and some slab settlement and future maintenance can be tolerated,we recommend that the slab area be over-excavated by a minimum of two feet and the slab-on- grade supported on a minimum of two feet of granular material (2-inch crushed rock) compacted to structural fill specifications. The slab should be additionally reinforced and doweled cold joints incorporated in the slab design, to further reduce the effects of differential settlement. Some slab settlement, differential settlement, and cracking should be expected, due to the existence of the loose undocumented fill soils. If no settlement of the slab can be tolerated, the slab should be designed as a structural slab and supported on pin piles. NELSON GEOTECHNICAL ASSOCIATES, INC.