3410 TERMINAL AVE 2018-03-09 - Laserfiche WebLink

M&N 8415-02 February 18,2015 As-Built Pile Axial Capacity and Soil Stiffness Memorandum As-Driven Pile Tip Elevations The Shannon & Wilson pile driving records show that all of the piles were driven at least to the recommended tip elevation shown in the contract documents. Piles in gridlines D, E, F, and G were typically driven to the design tip elevation, while piles on gridlines B and C were typically driven 5 feet deeper than the design tip elevation. Pile Axial Geotechnical Capacities A review of the PDA and CAPWAP analysis results indicate that all of the piles tested reached or exceeded the minimum axial capacity indicated in the contract documents.Note that all of the test piles were tested before the piles had been driven fully to the design tip elevation. Most of the as-tested piles were 1 to 2 feet above the tip elevation. Despite this,the piles were shown to have adequate axial capacity.The piles were driven down to their design tip elevation after the PDA testing had been conducted. Soil-Pile Axial Stiffness A review of the PDA and CAPWAP analysis results indicate that the axial response of the soil-pile system was softer than expected.In design and analysis of the upgrades it was assumed that the axial soil stiffness was taken to equal 2,000 kips/in for both the existing and new piles. This was slightly softer than the stiffness recommended by Shannon & Wilson based on their experience with similar soils in the Puget Sound Region. The CAPWAP analyses indicated that the soil axial stiffness was between 500 kips/in and 2,000 kips/in depending on the axial load in the pile. This variation is due to the nonlinear softening behavior of the soil under load.For loads under approximately 390 kips,the soil responded elastically with a stiffness of approximately 1,800 to 2,000 kips/in. However,for pile loads over 390 kips,the soil begins to soften down to approximately 500 kips/in in the worst case.This behavior can be seen in the pile axial load v.secant stiffness plot provided by Shannon&Wilson in Appendix B. Soil flexibility was modeled during design using axial springs at the pile tip. During analysis it was found that the flexural demands in the existing pile cap were moderately sensitive to the soil spring values.As the spring stiffnesses were decreased the positive flexural moment in the existing pile cap increased for all loading cases considered(1000psf uniform live load,Terex HMK 7608 mobile harbor crane operational and travelling loading, and Gottwald HMK 280E mobile harbor crane operational and travelling loading). Because the existing pile caps were at almost 100 percent utilization for positive moment during design, a reduction in soil spring stiffness would cause the pile cap demands to exceed the member capacity. All other components were found to be either insensitive to the spoil spring stiffness, or had adequate capacity to resist any increased demands. In order to determine the impacts of the softer soil springs,the pile factored axial demands for each load combination were compared to the Shannon & Wilson axial load v. secant stiffness plots. For all four mobile harbor crane load combinations(HMK 7608 operating, HMK 7608 travelling,HMK 280E operating, and HMK 280E travelling), the maximum factored axial load was 360 kips. As mentioned previously for axial loads less than 390 kips, the as-built pile stiffness was approximately 2000 kips/in.This is the same ,ir,iti r,i,: 2 (/ / y.