2102 ROSS AVE 2018-02-23 - Laserfiche WebLink

McClean Iron Works Pier Project NGA File No. 7903B16 2102 Ross Avenue October 28, 2016. Everett,Washington Page 3 (52 kips) at a deflection of less than 0.2 inch and based on those results, NGA recommended a design capacity of 22 tons(44 kips)at a refusal criterion of less than 2 inches of penetration per minute of driving. PRELIMINARY OPINIONS AND RECOMMENDATIONS It is our understanding that the plan is to drive 18-inch diameter pipe piles with a vibratory hammer, allow the excess pore water pressures to dissipate and the soils to gain strength and then to proof-test the piles by striking them with an impact hammer(air, steam, or Diesel). Culbertson Marine will install the piles. Piles will derive their support from both skin friction and end bearing. For design purposes,we assumed that fill below the water table and some of the looser alluvial silty sands will liquefy during a seismic event. Skin friction within the liquefied zones was neglected in the determination of the axial capacity of each pile. The axial capacities of the piles have also been reduced to account for the effects of down drag forces that might occur due to the dynamic settlement of the soils within and above the liquefiable zone. Based on our analyses,the recommended allowable axial capacity per pile is 50 tons,provided the piles are driven a minimum of 15 feet into medium dense sands found at depth, and meet a refusal criterion of less than 2 inches of penetration per minute of continuous driving with a vibratory hammer with an energy rating of 4,000 foot-pounds. Of the two vibratory hammers owned by Culbertson Marine,we recommend installing the pipe piles with the Foster 4000 vibratory hammer. The J & M 416L hammer appears to be slightly undersized for the pile size and is not recommended. The allowable pile capacity can be increased by 33 percent for dynamic loading conditions. To keep capacity reductions from group effects to a negligible amount, all piles should have a minimum center-to-center spacing of at least 3 pile diameters. Assuming that the subsurface soil and groundwater conditions at the pier location are similar to those encountered in the explorations by others, pile lengths of approximately 60 feet should be assumed. However, the composition of alluvial deposits commonly varies with location and depth and therefore subsurface conditions at the pier location could differ significantly. We note that the pin piles installed in 2008 and 2009 varied from approximately 34 feet to 107 feet in length and approximately 12 percent of the piles were longer than 60 feet. Accordingly,NGA recommends that a test pile be installed to evaluate pile capacity with depth of penetration and to confirm or revise the estimated pile length. The test pile should be installed within the pier footprint and located at a point that is the farthest away from any of the previously installed piles. NELSON GEOTECHNICAL ASSOCIATES, INC.