Influence of axially loaded shaped pile on geotechnical capacity
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Date
2016
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Publisher
Universiti Teknologi Malaysia
Abstract
The current methods for pile design were developed based on experimental and theoretical studies derived using circular piles. In practice, pile designers convert the cross sectional (base) area of circular piles to the equivalent area of the new cross section, without recourse to any other effect of the new geometry. This research examines the influence of cross sectional geometry on the axial capacity of piles. Model piles of four different cross sections: circular, hexagonal, octagonal, and square of two lengths, each depicting long and short piles were employed. Five unique inverted-vee-shaped dents were used to form ribs on another two circular piles to model ribbed piles. The piles were installed in Kaolin S300 soil model and model pile load tests depicting Constant Rate of Penetration (CRP) method in the field were performed. The measured capacities, Qm of the piles were obtained using six different interpretation methods. The results revealed that the capacity increase of the square, hexagonal and octagonal piles over the circular pile are 20.30%, 9.64% and 4.68% for long piles and 19.66%, 10.73% and 6.76% for short piles, respectively. Also, the capacity of ribbed piles are higher by 31.73% and 18.90% over their corresponding plain piles for short and long piles respectively. Hansen 80% and Chin methods produced the best results for the model tests relative to the predicted capacity, Qp of the model piles. The displacement of soils beneath the differently shaped piles was observed during penetration tests in transparent synthetic soil made from fumed silica aggregates and pore fluid containing Paraffin and White Oil. GeoPIV8; a MATLAB based Particle Image Velocimetry (PIV) software was employed for the analysis of the images captured during the penetration tests. The PIV results showed that the displacements of soil beneath the square pile align perfectly vertical with the vertical edge of the pile, while it inclined with the vertical for the piles of other shapes. This angle of inclination O also varies for the variously shaped piles. Finally, scale-up prototypes of the model piles were numerically analysed using Plaxis 3D Foundation. Linear elastic and Mohr-Coulomb constitutive models were employed to model the piles and soil, respectively. The results revealed that the capacities of the square, hexagonal and octagonal piles are higher by 24.32%, 16.22% and 6.08% respectively over that of circular pile for the long piles, and the capacities are higher by 22.31%, 15.70% and 6.61%, respectively for the short piles. The results harmonized with those of physical modelling. In conclusion, the need to characterise the base area of the new shape of pile with a factor of its perimeter while it is being adopted in lieu of circular pile was affirmed in this research
Description
Thesis (PhD. (Civil Engineering))
Keywords
Geotechnical engineering, Structural engineering—Research, Load factor design