PileGroup Validation - Example 1. Pile group in sand with battered piles (Davisson and Salley 1970)

This validation example is based on the model test results of a group of piles embedded in sand as reported in Davisson and Salley (1970). A group of six tubular aluminium piles of external diameter of 12.7 mm and wall thickness of 0.8 mm. The piles were embedded in a tank of dry fine sand to a depth of 0.533 m and loaded through a pile cap just above the level of the sand surface. The shear modulus (G) of the sand is proportional to the depth below the sand surface with the ratio of 2.4 MPa/m. The poison’s ratio for the sand is 0.25. The pile-to-cap connection was rigid for all piles. The layout of the pile group is shown in the figure below.

Figure 1-1 Pile group layout for Example 1

The analysis method for this example is based on the linear analysis module of the PileGroup program where Randolph’s elastic solutions for single piles in homogeneous or Gibson-type soils are adopted. The method assumes small-strain, elastic soil response and provides closed-form solutions for pile head displacement, rotation, and stiffness under vertical, lateral, and moment loading. Figure 1-2 and Figure 1-3 show the axial and lateral stiffness input parameters, respectively.

Figure 1-2 Axial stiffness inputs for linear analysis mode

Figure 1-3 Lateral stiffness inputs for linear analysis mode

The figure below shows the three-dimensional view of this 3 x 2 pile group modelled in the PileGroup program.

Figure 1-4 Three-dimensional view of 3 x 2 pile group

The figure below shows the soil layer information, pile group and pile cap loads defined in the program. It shows the thickness values for all the layers and the pile lengths.

Figure 1-5 Soil layers, soil properties and pile cap loads defined for this example.

Figure 1-6 shows the pile deflection results within the pile group from the analysis using the PileGroup program. Figure 1-7 shows the bending moment results within the pile group.

Figure 1-6 Pile deflections for Example 1

Figure 1-7 Pile moment for Example 1

Table 1-1 presents a comparison of the analysis results obtained from different programs. The axial load and lateral shear force results at the pile heads, as computed by the PileGroup program, show strong agreement with those calculated by both the PIGLET and PGROUP programs. This consistency indicates that the PileGroup program provides reliable results for these response parameters when compared with established analysis tools.

Regarding the bending moment at the pile heads, the results produced by the PileGroup program align closely with those obtained from the PIGLET program, as documented in Randolph (2021). However, it is important to note that both the PileGroup and PIGLET programs yield bending moment values that differ from those provided by the PGROUP program.

According to Randolph (2021), this discrepancy may be attributed to the underlying assumptions used in the PGROUP analysis. Specifically, PGROUP employs a homogeneous shear modulus for the soil, which could influence the resulting bending moment estimates and contribute to the observed differences.

Table 1-1 Comparison results for Example 1

References:

1. Davisson, M. T., and Salley, J. R. (1970). Model studies of laterally loaded piles. Journal of the Soil Mechanics and Foundations Division, ASCE, 96(SM5), 1605–1630.

2. Randolph, M. F. (2021). PIGLET: Analysis and Design of Pile Groups (Version 6.2). User Manual released June 2021.