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Geocentrix Repute - Onshore pile design and analysis

Bridge abutment on two rows of piles, one raked

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.

The loads applied to the pile cap are V = 8MN, H = 1.2MN, and M = 2.4MNm.


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
  Answers within 10% of benchmark
  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

 

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:

Pile rake Row spacing (Sx)
2m 3m
None Download Download
1:8 Download Download
1:6 Download Download
1:4 Download Download
 

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