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Geocentrix Repute - Onshore pile design and analysis

3-pile group under general loading

The following example [1] describes a group of 3 piles under general loading conditions. Three types of analysis are described:

  • A simple statical method that ignores the presence of soil and considers the pile group as a purely structural system
  • The equivalent-bent method that reduces the pile group to a structural system but takes some account of the effect of the soil by determining equivalent free-standing lengths of the piles
  • Pile group programs that consider the presence of the soil, including the interaction effects between the piles through the soil, specifically Repute, DEFPIG, Piglet, and GEPAN [2]

The 3-pile group is subjected to a combination of axial load, lateral load and moment. Results from the above methods are compared in Table 1 in which w3, u, and θ are the vertical head displacement of Pile 3, the horizontal cap displacement and the rotation of the cap, respectively. Resulting loads and bending moments at the pile heads are also reported.


Results from Repute

The results from Repute are given in the table below.

Comparison with benchmark

Variable Equivalent Beam Statical analysis DEFPIG Piglet GEPAN Repute
V1 (kN) 67.2 75.0 55.8 55.7 54.0 49.6
V2 (kN) 200.0 200.0 155.1 155.0 156.0 153.0
V3 (kN) 332.8 325.0 389.1 389.3 390.0 397.0
H1 (kN) 66.6 66.7 72.0 80.4 73.7 68.9
H2 (kN) 66.7 66.7 56.0 39.3 50.9 53.5
H3 (kN) 66.6 66.7 72.0 80.4 75.4 77.6
M1 (kN) -6.2 0 -35.8 -42.0 -38.5 -41.5
M2 (kN) -6.2 0 -28.5 -16.3 -26.1 -31.8
M3 (kN) -6.2 0 -35.8 -42.0 -38.6 -44.0
w3 (mm) 17.5 n/a 13.4 9.9 10.8 14.1
u (mm) 8.9 n/a 11.6 11.4 10.5 11.5
theta (rad) 0.00581 n/a 0.00242 0.00242 0.00241 0.00263

n/a = not available

Comments

There is a good agreement between the solutions which consider pile-soil-pile interaction (even if with different degrees of rigour), whereas the statical and equivalent-bent analyses give quite different results, thereby showing the pitfall of attempting to model a complex pile-soil system by means of a simple structural frame.

Reference

[1] Poulos H. G. & Davis, E. H. (1980). Pile foundation analysis and design. Wiley, New York.

[2] Xu K. J. & Poulos H. G. (2000). General elastic analysis of pile groups. Int. J. Numer. Anal. Meth. Geomechs 24, 1109-1138.

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