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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
rigid raft) and the results are presented in Figure 6. As expected,
Figure 6 shows that the load transmitted by the piles was
reduced as the raft width increased. It is noted that the piles load
decreased sharply until it reached a constant value at about 18%
of the total displacement. As the raft width increased from 4 m
to 7 m, the load transferred through the piles decreased by about
22%. As the load carried by the raft increases, however, it is
important to carefully examine the total and differential
settlements, which may rise due to the high level of stress
beneath the raft.
The spacing between piles can be used to evaluate the raft
flexibility instead of its width using Eq. 2.
The percentage of load transmitted by the piles decreases by
about 22% as the raft width doubled within the range
considered.
The percentage of load carried by piles increases as the pile
diameter increases. However, the rate of increase is higher for
small size piles and diminishes as the pile diameter increases.
3.3
Effect of pile diameter.
The pile diameter has a significant effect on its load carrying
capacity and stiffness, which can affect the performance of the
piled raft. To examine the effect of pile diameter on its load
share in piled raft design, a raft with width, B = 7.2 m and piles
spaced at S/D =4 is considered with pile diameter varying from
0.3 m to 0.9 m. Figure 7 demonstrates the percentage of load
carried by the piles as the pile diameter changes. The load
transferred by the piles increased from 18% to 33% of the total
load as the pile diameter increased from 0.3 m to 0.9 m. The
increase occurred because the piles started to interact with the
soil across a larger surface area and thus more load carried by
the piles. However, the effect of the pile diameter on the piles
load share diminishes as the diameter reaches the higher end of
the range considered. For example, the percentage of load taken
by the piles increased by about 2% as the diameter increased
from 0.7 to 0.9 m, while the difference for a smaller diameter
was about 9% as the diameter increased from 0.3 to 0.5 m.
Additional studies are required to evaluate the performance of a
flexible piled raft considering the number of piles, pile length
and loading scheme.
5 REFERENCES
Brown, P. T. 1969. Numerical Analyses of Uniformly Loaded Circular
Rafts on Deep Elastic Foundations.
Géotechnique
19 (3), 399-404.
Burland, J. B., Broms, B. B., and De Mello, V. B. 1978. Behaviour of
foundations and structures.
Proc. 9th ICSMFE.
Tokyo: V. 2, 496-546.
Clancy, P., and Randolph, M. F. 1993. An Approximate Analysis
Procedure for Piled Raft foundations.
International Journal for
Numerical and Analytical Methods in Geomechanics
17(12),849-869.
Horikoshi, K., and Randolph, M. F. 1996. Centrifuge modelling of piled
raft foundations on clay.
Géotechnique
, 46 (4), 741-752.
Horikoshi, K., Matsumoto, T., Hashizume, Y., and Watanabe, T. 2003b.
Performance of Piled Raft Foundations Subjected to Dynamic
Loading.
International Journal of Physical Modelling in Geotechnics
,
3 (2), 51-62.
Horikoshi, K., Matsumoto, T., Hashizume, Y., Watanabe, T., and
Fukuyama, H. 2003a. Performance of Piled Raft Foundations
Subjected to Static Horizontal Loads.
International Journal of
Physical Modelling in Geotechnics
3 (2), 37-50.
Horikoshi, K., Watanabe, T., Fukuyama, H., and Matsumoto, T. 2002.
Behaviour of Piled Raft Foundations Subjected to Horizontal Loads.
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Newfoundland, Canada: Taylor & Francis.
Katzenbach, R., Arslan, U., Moorman, C., and Reul, O. 1998. Piled Raft
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Matsumoto, T., Fukumura, K., Horikoshi, K., and Oki, A. 2004b.
Shaking Table Tests on Model Piled Rafts in Sand Considering
Influnce of Superstructures.
International Journal of Physical
Modelling in Geotechnics
4 (3), 21-38.
Figure 6. Load carried by the piles with different raft width.
Matsumoto, T., Fukumura, K., Pastsakorn, K., Horikoshi, K., and Oki,
A. 2004a. Experimental and Analytical Study on Behaviour of Model
Piled Raft in Sand Subjected to Horizontal and Moment Loading.
International Journal of Physical Modelling in Geotechnics
4(3),1-19.
Mayne, P. W., & Poulos, H. G. (1999). Approximate Displacement
Influence Factors for Elastic Shallow Foundations.
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Poulos, H. G. 2000. Practical Design Procedures for Piled Raft
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Poulos, H. G. 2001. Piled Raft Foundations: Design and Applications.
Geotechnique
51 (2), 95-113.
Poulos, H. G., and Davis, E. H. 1980.
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for Tall Buildings.
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42 (2), 78-84.
Figure 7. Load carried by the piles with different pile diameters.
4 CONCLUSIONS
Some of factors that affect the load sharing between the piles
and raft in a piled raft foundation were examined using a 3D
finite element model that has been calibrated/ verified by
comparing its predictions with measurements made in a
geotechnical centrifuge study. Based on the results of the 3D-
FEA, a number of conclusions can be drawn as follows:
Randolph, M. F. 1994. Design Methods for Piled Groups and Piled
Rafts.
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, 61-82. New Delhi, India.
Ta, L. D., and Small, J. C. 1996. Analysis of Piled Raft System in
Layered Soils.
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20 (1), 57-72.
Tomlinson, M. J. 1996.
Foundation Design and Construction.
London:
Longman Publishing Group.
The load share carried by piles is higher for a rigid raft (K
f
>
10) due to the minimal interaction between the raft and
subsoil compared to the perfectly flexible raft (K
f
< 0.01).
