Dynamic Testing Results for Piles Driven at Nucor Yamato Steel - Blytheville Arkansas Test Site

The New Madrid Seismic Zone (NMSZ), located within the Mississippi Embayment, has produced large earthquakes with detrimental effects due to deep soil deposits and resulting high peak horizontal ground accelerations. The alluvial soil deposits within the Mississippi Embayment include loose sands that are located below the ground water table; these sands are susceptible to liquefaction. Deep foundations are commonly used to prevent direct and indirect economic losses from liquefaction. However, settlement (downdrag) within the liquefied sand can cause downward friction (dragload) to develop on the perimeter of each deep foundation, increasing the load and leading to excessive settlement. In the absence of field measurements, engineers are uncertain about the amount of downward friction that will develop and how much settlement will occur.
To remedy this lack of understanding, small explosive charges were used to produce liquefaction under full-scale conditions and downdrag and dragload measurements were obtianed. Primary support for this project was provided by the Nucor Yamato Steel; however, supplemental funding from NSF was used to expand the scope of the project. The results from these tests will allow engineers to evaluate the accuracy of existing design procedures and develop modifications to produce better agreement with measured behavior. Improved design procedures will allow engineers to design safe yet cost-effective foundation solutions that will remain stable during earthquakes. Limitations of the previous study at the Turrell Arkansas Test Site were overcome during testing at the Blytheville Arkansas Test Site by 1) testing groups of piles instead of individual piles, 2) ensuring the neutral plane develops prior to blasting, and 3) ensuring the neutral plane redevelops following blasting. Two pile groups were instrumented, installed, pre-loaded, and subjected to a liquefaction event. Seven, closed-ended, 74-feet long by 18-inch diameter pipe piles and seven 90-feet long HP14x102 H-piles were installed and tested for this project.