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This is Example 2 from the PIGLET User Manual [1]. It deals
with a 2 x 4 pile group, in which one row of piles is raked in
the direction of the horizontal load.
The concrete piles (17m long, 0.6m in diameter) are spaced at
either 2 or 3m centres in
the X-direction (Sx) and at 2m centres in the Y-direction
(Sy). Young's
modulus of the piles is assumed to be 24GPa axially
and laterally. The bottom of the pile cap is 1.5m above the ground
surface.
The ground
itself has a shear modulus G = 1z MPa
(where
z is the depth below the bottom of the pile cap) and Poisson's
ratio = 0.2.
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The loads applied to the pile cap are V = 8MN, H = 1.2MN, and M = 2.4MNm.
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Results from Repute
| Row spacing Sx (m) |
Pile rake |
Deflection (mm) |
Maximum moment (kNm) |
| Vertical |
Horizontal |
Raked row |
Vertical row |
| 2 |
None |
17.0 |
33.5 |
-389 |
-354 |
| 1:8 |
15.1 |
16.1 |
-151 |
-130 |
| 1:6 |
15.0 |
11.9 |
-81 |
-64 |
| 1:4 |
15.1 |
5.3 |
+43 |
+62 |
| 3 |
None |
16.3 |
29.4 |
-417 |
-377 |
| 1:8 |
14.7 |
14.8 |
-191 |
-164 |
| 1:6 |
14.6 |
11.0 |
-122 |
-98 |
| 1:4 |
14.9 |
4.7 |
+5 |
+30 |
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Answers within 10% of benchmark |
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Answers within 20% of benchmark |
Comparison with benchmark
PIGLET (October 1996) obtains...
| Row spacing Sx (m) |
Pile rake |
Deflection (mm) |
Maximum moment (kNm) |
| Vertical |
Horizontal |
Raked row |
Vertical row |
| 2 |
None |
17.2 |
33.8 |
-339 |
-339 |
| 1:8 |
15.4 |
15.4 |
-90 |
-158 |
| 1:6 |
15.3 |
11.1 |
+42 |
-101 |
| 1:4 |
15.4 |
4.3 |
+132 |
+44 |
| 3 |
None |
16.6 |
29.5 |
-370 |
-370 |
| 1:8 |
15.1 |
14.3 |
-133 |
-195 |
| 1:6 |
14.9 |
10.4 |
-57 |
-137 |
| 1:4 |
15.1 |
3.9 |
+90 |
+32 |
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Comments
Repute and PIGLET give very
similar deflections for this example, but Repute generally gives
higher bending moments. PIGLET does not account for load-deformation
coupling, i.e. the interaction between the axial and lateral response
of the piles. This behaviour is important
when a pile group is
subjected to a combination of vertical and horizontal loads. Proper
consideration of this interaction (as in the Repute analysis) increases
bending moments in the leading/raked piles and decreases moments
in the trailing/vertical row [2].
Reference
[1] Randolph,
M. F. (1996). PIGLET analysis and design of pile groups, University
of Western Australia.
[2] Basile, F. (2003). Analysis and design of pile groups. In
Numerical Analysis and Modelling in Geomechanics (ed. J. W. Bull),
Spon press,
London, Chapter 10, pp 278-315.
Downloads
Repute
projects for this example:
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