330 ELM ST VIEW RIDGE ESTATES 2022-04-04

Geotechnical Engineering Evaluation NGA File No. 1085419 View Ridge Estates 330 Building Settlement March 22,2019 Everett,Washington Page 8 Pin Piles: For 2-inch diameter pipe piles driven to refusal using a hand-held, 140-pound jackhammer,we recommend a design axial compression capacity of three 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 for the 2-inch pin piles. 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. The pin piles should penetrate a minimum of ten 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 15 to 25 feet below the ground surface 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 two feet apart to avoid a grouping effect on the piles. We should also be retained to observe pin pile installation during construction. Helical Anchors: In the case of the helical anchors, the contractor should determine the torque values required to achieve the desired capacity. Load carrying capacities on the order of 15 kips or more could be achieved using 8- to 10-inch diameter helical anchors installed successfully. However, the anchors should meet refusal and be sized correctly to achieve these capacities. The overall size and type of helical anchor should be determined by the contractor and structural engineer to handle the anticipated loads. The anchors should be spaced a minimum of three times the diameter of the largest helix of the anchor on center. A minimum of two anchors should be tested to confirm design capacities. We recommend that we review anchor design and proposed installation methods. We should also observe anchor installation and testing. Two anchors should be performance tested to 200 percent of the anchor design capacity. The performance test should consist of cyclic loading in increments of 25 percent of the design load, as outlined in the Federal Highways Administration(FHA)report No. FHWA/RD-82/047. The test location should be determined in the field,based on soil conditions observed during anchor installation. Slab-on-Grade Repairs We understand the slab-on-grade area within the eastern portions of the building may need repairs in some areas. Slabs placed on fill could be at risk for cracking and settlement over time. If no settlement of the new slab can be tolerated,the new slab should be designed as a structural slab and supported on pin piles or helical anchors. If some settlement, cracking, and future maintenance of the new slab can be tolerated, the existing fill should be partially over-excavated and replaced with crushed rock. We recommend that at least 12 inches of the undocumented fill found below the slab be overexcavated and \1:\ NELSON GEOTECHNICAL ASSOCIATES, INC.