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AN EXPERIMENTAL STUDY OF THE BASE AND SHAFT RESISTANCE OF PIPE PILES INSTALLED IN SAND
The base and shaft resistance of steel pipe piles installed in silica sand is affected by several factors; these include but are not limited to: shaft resistance degradation, shaft surface roughness, installation method, pile geometry, soil density and particle size, and setup. This thesis focuses on the first four factors, while also considering the effect of soil density within each factor. Several of the pile design formulas available do not consider the effects of shaft resistance degradation due to load cycles during installation of jacked and driven closed-ended pipe piles, plug formation and evolution during driving of open-ended pipe piles, the degree of corrosion or pitting corrosion on the shaft surface of a pile and its potential impact on setup, and the geometry of the tip of the pile. To assess the impact on pile capacity of some of these factors, a series of static compression load tests were performed in a controlled environment in a calibration chamber with a scaled down instrumented model pile. The air-pluviation technique with different combination of sieves assembled in a large-scale pluviator was used to prepare F-55 sand samples of different density in the calibration chamber. Slight changes were made to the experimental setup to study each factor: sand sample density, driving energy, mode of installation, and geometry and shaft roughness of the model pile.
The results from the experiments confirmed that each of these factors affects the pile resistance. Some of the important conclusions were:
i. The shaft resistance of the model pile is about 2.4 times greater for jacked piles than for driven piles in dense sand, due to the greater shaft resistance degradation in driven piles.
ii. Despite the effect of degradation, the shaft resistance of the non-displacement model pile which had no loading cycles was a ratio of 0.37 to that of the driven model pile in medium dense sand and 0.60 in dense sand, due to the absence of displacement.
iii. An increase in the surface roughness of the jacked model piles from smooth to medium-rough resulted in an increase of the shaft resistance, which had a ratio of 7.75 to the smooth pile in dense sand and 3.05 in medium dense sand. An increase from smooth to rough resulted in an increase of the shaft resistance, which had a ratio of 8.00 to the smooth pile in dense sand and 4.26 in medium dense sand.
iv. Although rougher interfaces produce greater interface friction angles than smooth interfaces with sand, once a limiting value of surface roughness is reached, shearing occurs in a narrow band in the sand in the immediate vicinity of the model pile, with the shaft resistance depending on the critical-state friction angle of the sand. This means the shaft resistance will not increase further with changes in pile surface roughness, due to the fact that the internal critical-state friction angle of the sand has been reached in the shear band during loading.
v. During installation, the conical-based pile had a higher penetration per blow compared to the flat based pile from 0 to 25.6B in medium dense sand and 0 to 20B in dense sand (B = base diameter). After the pile was installed beyond 25.6B in medium dense and 20B in dense sand, the penetration per blow was identical.
vi. The base resistance of a conical-based model pile was about 0.76 times that of a flat-based model pile in dense sand and 0.56 in medium dense sand.
vii. Jacked piles had similar base resistance ratio of about 0.93 to 0.95 of driven piles in dense sand and 0.98 to 1.05 in medium dense sand. However, they had a much higher shaft resistance ratio of about 1.67 to 2.07 in dense sand and 1.44 to 1.50 in medium dense sand.
- Doctor of Philosophy
- Civil Engineering
- West Lafayette