Capacity of vertically loaded piles in low density sands.
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Date
2011-05-26
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Abstract
The reduction of pile capacity associated with volume contraction of the soil close to the pile
surface has been reported in carbonate deposits offshore North West Australia and in residual
deposits of Southern Africa.
Knowledge of the load carried by the shaft and the pile tip is critical for the determination of the
load settlement behavior of piles in structurally unstable and highly variable sand deposits. While
the Static and Dynamic formulas and Pile load tests are used for the determination of pile
carrying capacity, they are limited in terms of site coverage, cost and adequacy of load settlement
data. Since the mode of shearing around a pile shaft is very similar to that observed in
the direct shear tests, it is thus cost effective to develop analytical methods based on controlled
laboratory model tests in order to predict load settlement behavior and bearing capacity of piles.
A simple shear apparatus was developed to investigate whether or not significant contractile
strains are induced in low density residual sands subject to simple shear strain and to study the
effect of such contractile strain of a soil close to the pile shaft on pile load settlement behavior.
The design and development of the simple shear apparatus was based on a new simple shear
stress equation. Series of constant normal stresses, constant normal stiffness and constant volume
tests were conducted on samples of Berea Sands compacted to low density in the new apparatus,
supported by moisture induced collapse settlement and matric suction tests. The tests revealed
significant volume contraction of Berea Sands due to imposed simple shear strain.
The tests data were fed into a new Winkler - type load transfer model and were used to determine
the load - transfer curves of vertically loaded piles. The curves revealed that both the loadsettlement
behavior and pile capacity in low density sands are dependent on the volume
contraction of the soil in the plastic zone close to the pile surface, horizontal stress normal to the
pile shaft and stiffness of the soil outside the plastic zone.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, 2005.
Keywords
Theses--Civil engineering., Piling (Civil engineering)