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Behavior of displacement piles in an overconsolidated clay

Gerald Andrew Miller, University of Massachusetts Amherst


At the National Geotechnical Experimentation Site (NGES) on the University of Massachusetts Amherst Campus, 44 pipe piles with diameters in the range of 60 to 168 mm and lengths of 1.5 to 10.7 m, were installed and load tested. The majority of piles were installed in a moderately plastic, varved clay crust with overconsolidation ratios in the range of 4 to 9. Open-ended and closed-ended (60$\sp\circ$ apex cone) piles were installed by driving and jacking. An extensive program of laboratory and in situ soil testing was also completed. Axial compressive load tests to failure were conducted at a predetermined time after installation and some piles were subjected to repeat load tests. Additionally, load tests were conducted on pile cone tips, independent of the pile shaft. Average unit skin friction was backcalculated from the interpreted pile failure load and estimated values of end-bearing. The investigation revealed that: (1) pile driving resulted in more intrusion of soil into the pile (less plugging), as compared to pile jacking; (2) plugging was a function of pile diameter and soil characteristics; (3) jacking resulted in higher skin friction capacity than driving; (4) skin friction capacity of piles depended on the degree of plugging; (5) pile skin friction capacity appeared to be a function of the lateral reconsolidation effective stress; (6) the operative lateral effective stress acting on the piles at failure appeared to vary over wide limits between values close to the at rest earth pressure (K$\sb{\rm o}$) and the reconsolidation lateral earth pressure K$\sb{\rm o}$), estimated from in situ test results; (7) the operative coefficient of friction at the soil-pile interface at failure was best estimated from the results of interface direct shear tests using remolded soil; and (8) repeat load tests on piles resulted in successively higher failure loads until the third load test, after which the capacity dropped slightly. The mechanism responsible appeared to be an increase in end-bearing. A new effective stress analysis for pile skin friction was proposed. The analysis allows for consideration of the installation method, degree of plugging during open-ended penetration and the estimated lateral stress conditions around displacement piles installed in overconsolidated clay.

Subject Area

Civil engineering

Recommended Citation

Miller, Gerald Andrew, "Behavior of displacement piles in an overconsolidated clay" (1994). Doctoral Dissertations Available from Proquest. AAI9434511.