PileGroup Validation - Example 3. Linear analysis for pile group under vertical load (Basile 2020)

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The example of a 3 x 3 pile group in Basile (2020) is analysed using the analysis mode of linear analysis based on elastic solutions in the PileGroup program. In this example, the piles are constructed in a homogeneous elastic soil layer with a Young’s modulus of 50 MPa and a Poisson’s ratio of 0.5. The Young’s modulus of the pile material is 30 GPa. The pile length is 20 m and the pile diameter is 1 m. The spacing between the piles is 3 m.

Figure 3-1 Pile group layout for Example 3 — **Figure 3-1** Pile group layout for Example 3

The pile cap is assumed to be rigid and the connection between the pile heads and pile cap is fully rigid (no rotation is allowed). The pile group layout is shown in Figure 3-1. Figure 3-2 and Figure 3-3 show the axial and lateral stiffness input parameters, respectively.

Figure 3-2 Axial stiffness inputs for linear analysis mode — **Figure 3-2** Axial stiffness inputs for linear analysis mode

Figure 3-2 Lateral stiffness inputs for linear analysis mode — **Figure 3-2** Lateral stiffness inputs for linear analysis mode

The figure below shows the three-dimensional view of this 3 x 3 pile group modelled in the PileGroup program. A vertical load of 9 MN is applied in the centre of the pile cap.

Figure 3-4 Three-dimensional view of 3 x 3 pile group — **Figure 3-4** Three-dimensional view of 3 x 3 pile group

Figure 3-5 Soil layers, soil properties and pile cap loads defined for this example. — **Figure 3-5** Soil layers, soil properties and pile cap loads defined for this example.

Basile (2020) used this example to compare the results from the program PGROUPN in REPUTE with PIGLET (Randolph 2004 & 2021) and DEFPIG (Poulos 1990). Figure 3-4 shows the pile axial forces within the pile group from the analysis using the PileGroup program. The maximum pile axial force is about 1313 kN. The ratio between the maximum and average pile axial force is about 1.31.

Figure 3-6 Pile axial forces for Example 3 — **Figure 3-6** Pile axial forces for Example 3

The pile settlement results from the PileGroup program are shown in Figure 3-7. The pile settlement is about 7.4 mm for the vertical load of 9 MN.

Figure 3-7 Pile settlement for Example 3 — **Figure 3-7** Pile settlement for Example 3

The comparison results from different programs are shown in Table 3-1 and the results from the PileGroup program are very close and practically identical to those calculated by REPUTE, PIGLET and DEFPIG programs.

Table 3-1 Comparison results for Example 3 — **Table 3-1** Comparison results for Example 3

References:

Basile, F. (2020). “Influence of cap rigidity on pile group design.” Piling 2020: Proceedings of the Piling 2020 Conference, British Geotechnical Association (ICE Publishing), University of Durham, UK, pp. 73–78
Poulos, H. G. (1990). DEFPIG User’s Manual. Centre for Geotechnical Research, The University of Sydney, Australia.
Randolph, M. F. (2021). PIGLET: Analysis and Design of Pile Groups (Version 6.2). User Manual released June 2021.